Passing data between view controllers

Question

I'm new to iOS and Objective-C and the whole MVC paradigm and I'm stuck with the following:

I have a view that acts as a data entry form and I want to give the user the option to select multiple products. The products are listed on another view with a UITableViewController and I have enabled multiple selections.

How do I transfer the data from one view to another? I will be holding the selections on the UITableView in an array, but how do I then pass that back to the previous data entry form view so it can be saved along with the other data to Core Data on submission of the form?

I have surfed around and seen some people declare an array in the app delegate. I read something about singletons, but I don't understand what these are and I read something about creating a data model.

What would be the correct way of performing this and how would I go about it?

Answer 1

This question seems to be very popular here on Stack Overflow so I thought I would try and give a better answer to help out people starting in the world of iOS like me.

Passing Data Forward

Passing data forward to a view controller from another view controller. You would use this method if you wanted to pass an object/value from one view controller to another view controller that you may be pushing on to a navigation stack.

For this example, we will have ViewControllerA and ViewControllerB

To pass a BOOL value from ViewControllerA to ViewControllerB we would do the following.

1. in ViewControllerB.h create a property for the BOOL

    @property (nonatomic, assign) BOOL isSomethingEnabled;
   

2. in ViewControllerA you need to tell it about ViewControllerB so use an

    #import "ViewControllerB.h"
   

Then where you want to load the view, for example, didSelectRowAtIndex or some IBAction, you need to set the property in ViewControllerB before you push it onto the navigation stack.

    ViewControllerB *viewControllerB = [[ViewControllerB alloc] initWithNib:@"ViewControllerB" bundle:nil];
    viewControllerB.isSomethingEnabled = YES;
    [self pushViewController:viewControllerB animated:YES];

This will set isSomethingEnabled in ViewControllerB to BOOL value YES.

Passing Data Forward using Segues

If you are using Storyboards you are most likely using segues and will need this procedure to pass data forward. This is similar to the above but instead of passing the data before you push the view controller, you use a method called

-(void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender

So to pass a BOOL from ViewControllerA to ViewControllerB we would do the following:

1. in ViewControllerB.h create a property for the BOOL

    @property (nonatomic, assign) BOOL isSomethingEnabled;
   

2. in ViewControllerA you need to tell it about ViewControllerB, so use an

    #import "ViewControllerB.h"
   

3. Create the segue from ViewControllerA to ViewControllerB on the storyboard and give it an identifier. In this example we'll call it "showDetailSegue"

4. Next, we need to add the method to ViewControllerA that is called when any segue is performed. Because of this we need to detect which segue was called and then do something. In our example, we will check for "showDetailSegue" and if that's performed, we will pass our BOOL value to ViewControllerB

    -(void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender{
        if([segue.identifier isEqualToString:@"showDetailSegue"]){
            ViewControllerB *controller = (ViewControllerB *)segue.destinationViewController;
            controller.isSomethingEnabled = YES;
        }
    }
   

If you have your views embedded in a navigation controller, you need to change the method above slightly to the following

    -(void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender{
        if([segue.identifier isEqualToString:@"showDetailSegue"]){
            UINavigationController *navController = (UINavigationController *)segue.destinationViewController;
            ViewControllerB *controller = (ViewControllerB *)navController.topViewController;
            controller.isSomethingEnabled = YES;
        }
    }

This will set isSomethingEnabled in ViewControllerB to BOOL value YES.

Passing Data Back

To pass data back from ViewControllerB to ViewControllerA you need to use Protocols and Delegates or Blocks, the latter can be used as a loosely coupled mechanism for callbacks.

To do this we will make ViewControllerA a delegate of ViewControllerB. This allows ViewControllerB to send a message back to ViewControllerA enabling us to send data back.

For ViewControllerA to be a delegate of ViewControllerB it must conform to ViewControllerB's protocol which we have to specify. This tells ViewControllerA which methods it must implement.

1. In ViewControllerB.h, below the #import, but above @interface you specify the protocol.

    @class ViewControllerB;
   
    @protocol ViewControllerBDelegate <NSObject>
    - (void)addItemViewController:(ViewControllerB *)controller didFinishEnteringItem:(NSString *)item;
    @end
   

2. Next still in the ViewControllerB.h, you need to set up a delegate property and synthesize in ViewControllerB.m

    @property (nonatomic, weak) id <ViewControllerBDelegate> delegate;
   

3. In ViewControllerB we call a message on the delegate when we pop the view controller.

    NSString *itemToPassBack = @"Pass this value back to ViewControllerA";
    [self.delegate addItemViewController:self didFinishEnteringItem:itemToPassBack];
   

4. That's it for ViewControllerB. Now in ViewControllerA.h, tell ViewControllerA to import ViewControllerB and conform to its protocol.

    #import "ViewControllerB.h"
   
    @interface ViewControllerA : UIViewController <ViewControllerBDelegate>
   

5. In ViewControllerA.m implement the following method from our protocol

    - (void)addItemViewController:(ViewControllerB *)controller didFinishEnteringItem:(NSString *)item
    {
        NSLog(@"This was returned from ViewControllerB %@", item);
    }
   

6. Before pushing viewControllerB to navigation stack we need to tell ViewControllerB that ViewControllerA is its delegate, otherwise we will get an error.

    ViewControllerB *viewControllerB = [[ViewControllerB alloc] initWithNib:@"ViewControllerB" bundle:nil];
    viewControllerB.delegate = self
    [[self navigationController] pushViewController:viewControllerB animated:YES];
   

---

References

1. Using Delegation to Communicate With Other View Controllers in the View Controller Programming Guide
2. Delegate Pattern

NSNotification center

It's another way to pass data.

// Add an observer in controller(s) where you want to receive data
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(handleDeepLinking:) name:@"handleDeepLinking" object:nil];

-(void) handleDeepLinking:(NSNotification *) notification {
    id someObject = notification.object // Some custom object that was passed with notification fire.
}

// Post notification
id someObject;
[NSNotificationCenter.defaultCenter postNotificationName:@"handleDeepLinking" object:someObject];

Passing Data back from one class to another (A class can be any controller, Network/session manager, UIView subclass or any other class)

Blocks are anonymous functions.

This example passes data from Controller B to Controller A

Define a block

@property void(^selectedVoucherBlock)(NSString *); // in ContollerA.h

Add block handler (listener)

Where you need a value (for example, you need your API response in ControllerA or you need ContorllerB data on A)

// In ContollerA.m

- (void)viewDidLoad {
    [super viewDidLoad];
    __unsafe_unretained typeof(self) weakSelf = self;
    self.selectedVoucherBlock = ^(NSString *voucher) {
        weakSelf->someLabel.text = voucher;
    };
}

Go to Controller B

UIStoryboard *storyboard = [UIStoryboard storyboardWithName:@"Main" bundle:nil];
ControllerB *vc = [storyboard instantiateViewControllerWithIdentifier:@"ControllerB"];
vc.sourceVC = self;
    [self.navigationController pushViewController:vc animated:NO];

Fire block

-(void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:
(NSIndexPath *)indexPath {
    NSString *voucher = vouchersArray[indexPath.row];
    if (sourceVC.selectVoucherBlock) {
        sourceVC.selectVoucherBlock(voucher);
    }
    [self.navigationController popToViewController:sourceVC animated:YES];
}

Another Working Example for Blocks

Answer 2

Swift

There are tons and tons of explanations here and around Stack Overflow, but if you are a beginner just trying to get something basic to work, try watching this YouTube tutorial (It's what helped me to finally understand how to do it).

• YouTube tutorial: How to send data through segue (Swift)

Passing data forward to the next View Controller

The following is an example based on the video. The idea is to pass a string from the text field in the First View Controller to the label in the Second View Controller.

Create the storyboard layout in the Interface Builder. To make the segue, you just Control click on the button and drag over to the Second View Controller.

First View Controller

The code for the First View Controller is

import UIKit

class FirstViewController: UIViewController {

    @IBOutlet weak var textField: UITextField!

    // This function is called before the segue
    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {

        // Get a reference to the second view controller
        let secondViewController = segue.destination as! SecondViewController

        // Set a variable in the second view controller with the String to pass
        secondViewController.receivedString = textField.text!
    }

}

Second View Controller

And the code for the Second View Controller is

import UIKit

class SecondViewController: UIViewController {

    @IBOutlet weak var label: UILabel!

    // This variable will hold the data being passed from the First View Controller
    var receivedString = ""

    override func viewDidLoad() {
        super.viewDidLoad()

        // Used the text from the First View Controller to set the label
        label.text = receivedString
    }

}

Don't forget

• Hook up the outlets for the UITextField and the UILabel.
• Set the first and second View Controllers to the appropriate Swift files in Interface Builder.

Passing data back to the previous View Controller

To pass data back from the second view controller to the first view controller, you use a protocol and a delegate. This video is a very clear walk though of that process:

• YouTube tutorial: iOS Swift Basics Tutorial: Protocols and Delegates But also read this post to make sure you don't get into a strong reference cycle.

The following is an example based on the video (with a few modifications).

Create the storyboard layout in the Interface Builder. Again, to make the segue, you just Control drag from the button to the Second View Controller. Set the segue identifier to showSecondViewController. Also, don't forget to hook up the outlets and actions using the names in the following code.

First View Controller

The code for the First View Controller is

import UIKit

class FirstViewController: UIViewController, DataEnteredDelegate {

    @IBOutlet weak var label: UILabel!

    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        if segue.identifier == "showSecondViewController" {
            let secondViewController = segue.destination as! SecondViewController
            secondViewController.delegate = self
        }
    }

    func userDidEnterInformation(info: String) {
        label.text = info
    }
}

Note the use of our custom DataEnteredDelegate protocol.

Second View Controller and Protocol

The code for the second view controller is

import UIKit

// Protocol used for sending data back
protocol DataEnteredDelegate: AnyObject {
    func userDidEnterInformation(info: String)
}

class SecondViewController: UIViewController {

    // Making this a weak variable, so that it won't create a strong reference cycle
    weak var delegate: DataEnteredDelegate? = nil

    @IBOutlet weak var textField: UITextField!

    @IBAction func sendTextBackButton(sender: AnyObject) {

        // Call this method on whichever class implements our delegate protocol
        delegate?.userDidEnterInformation(info: textField.text!)

        // Go back to the previous view controller
        _ = self.navigationController?.popViewController(animated: true)
    }
}

Note that the protocol is outside of the View Controller class.

That's it. Running the app now, you should be able to send data back from the second view controller to the first.

Answer 3

The M in MVC is for "Model" and in the MVC paradigm the role of model classes is to manage a program's data. A model is the opposite of a view -- a view knows how to display data, but it knows nothing about what to do with data, whereas a model knows everything about how to work with data, but nothing about how to display it. Models can be complicated, but they don't have to be -- the model for your app might be as simple as an array of strings or dictionaries.

The role of a controller is to mediate between view and model. Therefore, they need a reference to one or more view objects and one or more model objects. Let's say that your model is an array of dictionaries, with each dictionary representing one row in your table. The root view for your app displays that table, and it might be responsible for loading the array from a file. When the user decides to add a new row to the table, they tap some button and your controller creates a new (mutable) dictionary and adds it to the array. In order to fill in the row, the controller creates a detail view controller and gives it the new dictionary. The detail view controller fills in the dictionary and returns. The dictionary is already part of the model, so nothing else needs to happen.

Answer 4

There are various ways by which data can be received by a different class in iOS. For example -

1. Direct initialization after the allocation of another class.
2. Delegation - for passing data back
3. Notification - for broadcasting data to multiple classes at a single time
4. Saving in NSUserDefaults - for accessing it later
5. Singleton classes
6. Databases and other storage mechanisms, like p-list files, etc.

But for the simple scenario of passing a value to a different class whose allocation is done in the current class, the most common and preferred method would be the direct setting of values after allocation. This is done as follows:

We can understand it using two controllers - Controller1 and Controller2

Suppose in Controller1 class you want to create the Controller2 object and push it with a String value being passed. This can be done as this:

- (void)pushToController2 {

    Controller2 *obj = [[Controller2 alloc] initWithNib:@"Controller2" bundle:nil];
    [obj passValue:@"String"];
    [self pushViewController:obj animated:YES];
}

In the implementation of the Controller2 class there will be this function as:

@interface Controller2  : NSObject

@property (nonatomic, strong) NSString* stringPassed;

@end

@implementation Controller2

@synthesize stringPassed = _stringPassed;

- (void) passValue:(NSString *)value {

    _stringPassed = value; // Or self.stringPassed = value
}

@end

You can also directly set the properties of the Controller2 class in the similar way as this:

- (void)pushToController2 {

    Controller2 *obj = [[Controller2 alloc] initWithNib:@"Controller2" bundle:nil];
    [obj setStringPassed:@"String"];
    [self pushViewController:obj animated:YES];
}

To pass multiple values, you can use the multiple parameters like:

Controller2 *obj = [[Controller2 alloc] initWithNib:@"Controller2" bundle:nil];
[obj passValue:@“String1” andValues:objArray withDate:date];

Or if you need to pass more than three parameters which are related to a common feature, you can store the values in a model class and pass that modelObject to the next class

ModelClass *modelObject = [[ModelClass alloc] init];
modelObject.property1 = _property1;
modelObject.property2 = _property2;
modelObject.property3 = _property3;

Controller2 *obj = [[Controller2 alloc] initWithNib:@"Controller2" bundle:nil];
[obj passmodel: modelObject];

So in short, if you want to -

1. set the private variables of the second class initialise the values by calling a custom function and passing the values.
2. setProperties do it by directlyInitialising it using the setter method.
3. pass more that 3-4 values related to each other in some manner, then create a model class and set values to its object and pass the object using any of the above process.

Answer 5

After more research it seemed that protocols and delegates were the correct/Apple preferred way of doing this.

I ended up using this example (in the iPhone development SDK):

Sharing data between view controllers and other objects

It worked fine and allowed me to pass a string and an array forward and back between my views.

Answer 6

I find simplest and most elegant version with passing blocks. Let's name view controller that waits for returned data as "A" and returning view controller as "B". In this example we want to get 2 values: first of Type1 and second of Type2.

Assuming we use Storyboard, first controller sets callback block, for example during segue preparation:

- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
    if ([segue.destinationViewController isKindOfClass:[BViewController class]])
    {
        BViewController *viewController = segue.destinationViewController;

        viewController.callback = ^(Type1 *value1, Type2 *value2) {
            // optionally, close B
            //[self.navigationController popViewControllerAnimated:YES];

            // let's do some action after with returned values
            action1(value1);
            action2(value2);
        };

    }
}

and "B" view controller should declare callback property, BViewController.h:

// it is important to use "copy"
@property (copy) void(^callback)(Type1 *value1, Type2 *value2);

Than in implementation file BViewController.m after we have desired values to return our callback should be called:

if (self.callback)
    self.callback(value1, value2);

One thing to remember is that using block often needs to manage strong and __weak references like explained here

Answer 7

There is some good information in many of the answers given, but none address the question fully.

The question asks about passing information between view controllers. The specific example given asks about passing information between views, but given the self-stated newness to iOS, the original poster likely meant between viewControllers, not between views (without any involvement from the ViewControllers). It seems that all the answers focus on two view controllers, but what if the app evolves to need to involve more than two view controllers in the information exchange?

The original poster also asked about Singletons and the use of the AppDelegate. These questions need to be answered.

To help anyone else looking at this question, who wants a full answer, I'm going to attempt to provide it.

Application Scenarios

Rather than having a highly hypothetical, abstract discussion, it helps to have concrete applications in mind. To help define a two-view-controller situation and a more-than-two-view-controller situation, I am going to define two concrete application scenarios.

Scenario one: maximum two view controllers ever need to share information.

See diagram one.

There are two view controllers in the application. There is a ViewControllerA (Data Entry Form), and View Controller B (Product List). The items selected in the product list must match the items displayed in the text box in the data entry form. In this scenario, ViewControllerA and ViewControllerB must communicate directly with each other and no other view controllers.

Scenario two: more than two view controllers need to share the same information.

See diagram two.

There are four view controllers in the application. It is a tab-based application for managing home inventory. Three view controllers present differently filtered views of the same data:

• ViewControllerA - Luxury Items
• ViewControllerB - Non-insured Items
• ViewControllerC - Entire Home Inventory
• ViewControllerD - Add New Item Form

Any time an individual item is created or edited, it must also synchronize with the other view controllers. For example, if we add a boat in ViewControllerD, but it is not yet insured, then the boat must appear when the user goes to ViewControllerA (Luxury Items), and also ViewControllerC (Entire Home Inventory), but not when the user goes to ViewControllerB (Non-insured Items). We need be concerned with not only adding new items, but also deleting items (which may be allowed from any of the four view controllers), or editing existing items (which may be allowed from the "Add New Item Form", repurposing the same for editing).

Since all the view controllers do need to share the same data, all four view controllers need to remain in synchronization, and therefore there needs to be some sort of communication to all other view controllers, whenever any single view controller changes the underlying data. It should be fairly obvious that we do not want each view controller communicating directly with each other view controller in this scenario. In case it is not obvious, consider if we had 20 different view controllers (rather than just 4). How difficult and error-prone would it be to notify each of the other 19 view controllers any time one view controller made a change?

The Solutions: Delegates and the Observer Pattern, and Singletons

In scenario one, we have several viable solutions, as other answers have given

• segues
• delegates
• setting properties on view controllers directly
• NSUserDefaults (actually a poor choice)

In scenario two, we have other viable solutions:

• Observer Pattern
• Singletons

A singleton is an instance of a class, that instance being the only instance in existence during its lifetime. A singleton gets its name from the fact that it is the single instance. Normally developers who use singletons have special class methods for accessing them.

+ (HouseholdInventoryManager*) sharedManager; {
    static dispatch_once_t onceQueue;
    static HouseholdInventoryManager* _sharedInstance;

    // dispatch_once is guaranteed to only be executed
    // once in the lifetime of the application
    dispatch_once(&onceQueue, ^{
        _sharedInstance = [[self alloc] init];
    });
    return _sharedInstance;
}

Now that we understand what a singleton is, let's discuss how a singleton fits into the observer pattern. The observer pattern is used for one object to respond to changes by another object. In the second scenario, we have four different view controllers, who all want to know about changes to the underlying data. The "underlying data" should belong to a single instance, a singleton. The "know about changes" is accomplished by observing changes made to the singleton.

The home inventory application would have a single instance of a class which is designed to manage a list of inventory items. The manager would manage a collection of household items. The following is a class definition for the data manager:

#import <Foundation/Foundation.h>

@class JGCHouseholdInventoryItem;

@interface HouseholdInventoryManager : NSObject
/*!
 The global singleton for accessing application data
 */
+ (HouseholdInventoryManager*) sharedManager;


- (NSArray *) entireHouseholdInventory;
- (NSArray *) luxuryItems;
- (NSArray *) nonInsuredItems;

- (void) addHouseholdItemToHomeInventory:(JGCHouseholdInventoryItem*)item;
- (void) editHouseholdItemInHomeInventory:(JGCHouseholdInventoryItem*)item;
- (void) deleteHoueholdItemFromHomeInventory:(JGCHouseholdInventoryItem*)item;
@end

When the collection of home inventory items changes, the view controllers need to be made aware of this change. The class definition above does not make it obvious how this will happen. We need to follow the observer pattern. The view controllers must formally observe the sharedManager. There are two ways to observe another object:

• Key-Value-Observing (KVO)
• NSNotificationCenter.

In scenario two, we do not have a single property of the HouseholdInventoryManager which could be observed using KVO. Because we do not have a single property which is easily observable, the observer pattern, in this case, must be implemented using NSNotificationCenter. Each of the four view controllers would subscribe to notifications, and the sharedManager would send notifications to the notification center when appropriate. The inventory manager does not need to know anything about the view controllers or instances of any other classes which may be interested in knowing when the collection of inventory items changes; the NSNotificationCenter takes care of these implementation details. The View Controllers simply subscribe to notifications, and the data manager simply posts notifications.

Many beginner programmers take advantage of the fact that there is always exactly one Application Delegate in the lifetime of the application, which is globally accessible. Beginning programmers use this fact to stuff objects and functionality into the appDelegate as a convenience for access from anywhere else in the application. Just because the AppDelegate is a singleton doesn't mean it should replace all other singletons. This is a poor practice as it places too much burden on one class, breaking good object-oriented practices. Each class should have a clear role that is easily explained, often just by the name of the class.

Any time your Application Delegate starts to get bloated, start to remove functionality into singletons. For example, the Core Data Stack should not be left in the AppDelegate, but should instead be put in its own class, a coreDataManager class.

References

• Managing Data Flow Between View Controllers
• Passing Data Between View Controllers
• Asynchronous JSON Requests in Objective-C

Answer 8

Passing data back from ViewController 2 (destination) to viewController 1 (source) is the more interesting thing. Assuming you use storyBoard, these are all the ways I found out:

• Delegate
• Notification
• User defaults
• Singleton

Those were discussed here already.

I found there are more ways:

Using Block callbacks:

Use it in the prepareForSegue method in the VC1

NextViewController *destinationVC = (NextViewController *) segue.destinationViewController;
[destinationVC setDidFinishUsingBlockCallback:^(NextViewController *destinationVC)
{
    self.blockLabel.text = destination.blockTextField.text;
}];

Using storyboards Unwind (Exit)

Implement a method with a UIStoryboardSegue argument in VC 1,like this one:

-(IBAction)UnWindDone:(UIStoryboardSegue *)segue { }

In the storyBoard, hook the "return" button to the green Exit button (Unwind) of the vc. Now you have a segue that "goes back" so you can use the destinationViewController property in the prepareForSegue of VC2 and change any property of VC1 before it goes back.

• Another option of using storyboards Undwind (Exit) - you can use the method you wrote in VC1

   -(IBAction)UnWindDone:(UIStoryboardSegue *)segue {
       NextViewController *nextViewController = segue.sourceViewController;
       self.unwindLabel.text = nextViewController.unwindPropertyPass;
   }
  

And in the prepareForSegue of VC1 you can change any property you want to share.

In both unwind options, you can set the tag property of the button and check it in the prepareForSegue.

Answer 9

The OP didn't mention view controllers but so many of the answers do, that I wanted to chime in with what some of the new features of the LLVM allow to make this easier when wanting to pass data from one view controller to another and then getting some results back.

Storyboard segues, ARC and LLVM blocks make this easier than ever for me. Some answers above mentioned storyboards and segues already but still relied on delegation. Defining delegates certainly works but some people may find it easier to pass pointers or code blocks.

With UINavigators and segues, there are easy ways of passing information to the subservient controller and getting the information back. ARC makes passing pointers to things derived from NSObjects simple so if you want the subservient controller to add/change/modify some data for you, pass it a pointer to a mutable instance. Blocks make passing actions easy so if you want the subservient controller to invoke an action on your higher level controller, pass it a block. You define the block to accept any number of arguments that makes sense to you. You can also design the API to use multiple blocks if that suits things better.

Here are two trivial examples of the segue glue. The first is straightforward showing one parameter passed for input, the second for output.

// Prepare the destination view controller by passing it the input we want it to work on
// and the results we will look at when the user has navigated back to this controller's view.

- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
    [[segue destinationViewController]

     // This parameter gives the next controller the data it works on.
     segueHandoffWithInput:self.dataForNextController

     // This parameter allows the next controller to pass back results
     // by virtue of both controllers having a pointer to the same object.
     andResults:self.resultsFromNextController];
}

This second example shows passing a callback block for the second argument. I like using blocks because it keeps the relevant details close together in the source - the higher level source.

// Prepare the destination view controller by passing it the input we want it to work on
// and the callback when it has done its work.

- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
    [[segue destinationViewController]

     // This parameter gives the next controller the data it works on.
     segueHandoffWithInput:self.dataForNextController

     // This parameter allows the next controller to pass back results.
     resultsBlock:^(id results) {
         // This callback could be as involved as you like.
         // It can use Grand Central Dispatch to have work done on another thread for example.
        [self setResultsFromNextController:results];
    }];
}

Answer 10

There are multiple methods for sharing data.

1. You can always share data using NSUserDefaults. Set the value you want to share with respect to a key of your choice and get the value from NSUserDefault associated to that key in the next view controller.

   [[NSUserDefaults standardUserDefaults] setValue:value forKey:key]
   [[NSUserDefaults standardUserDefaults] objectForKey:key]
   

2. You can just create a property in viewcontrollerA. Create an object of viewcontrollerA in viewcontrollerB and assign the desired value to that property.

3. You can also create custom delegates for this.

Answer 11

Swift 5

Well Matt Price's answer is perfectly fine for passing data, but I am going to rewrite it, in the latest Swift version because I believe new programmers find it quit challenging due to new syntax and methods/frameworks, as original post is in Objective-C.

There are multiple options for passing data between view controllers.

1. Using Navigation Controller Push
2. Using Segue
3. Using Delegate
4. Using Notification Observer
5. Using Block

I am going to rewrite his logic in Swift with the latest iOS framework

---

Passing Data through Navigation Controller Push: From ViewControllerA to ViewControllerB

Step 1. Declare variable in ViewControllerB

var isSomethingEnabled = false

Step 2. Print Variable in ViewControllerB' ViewDidLoad method

override func viewDidLoad() {
    super.viewDidLoad()
    // Print value received through segue, navigation push
    print("Value of 'isSomethingEnabled' from ViewControllerA: ", isSomethingEnabled)
}

Step 3. In ViewControllerA Pass Data while pushing through Navigation Controller

if let viewControllerB = UIStoryboard(name: "Main", bundle: nil).instantiateViewController(withIdentifier: "ViewControllerB") as? ViewControllerB {
    viewControllerB.isSomethingEnabled = true
    if let navigator = navigationController {
        navigator.pushViewController(viewControllerB, animated: true)
    }
}

So here is the complete code for:

ViewControllerA

import UIKit

class ViewControllerA: UIViewController  {

    override func viewDidLoad() {
        super.viewDidLoad()
    }

    // MARK: Passing data through navigation PushViewController
    @IBAction func goToViewControllerB(_ sender: Any) {

        if let viewControllerB = UIStoryboard(name: "Main", bundle: nil).instantiateViewController(withIdentifier: "ViewControllerB") as? ViewControllerB {
            viewControllerB.isSomethingEnabled = true
            if let navigator = navigationController {
                navigator.pushViewController(viewControllerB, animated: true)
            }
        }
    }
}

ViewControllerB

import UIKit

class ViewControllerB: UIViewController {

    // MARK:  - Variable for Passing Data through Navigation push
    var isSomethingEnabled = false

    override func viewDidLoad() {
        super.viewDidLoad()
        // Print value received through navigation push
        print("Value of 'isSomethingEnabled' from ViewControllerA: ", isSomethingEnabled)
    }
}

---

Passing Data through Segue: From ViewControllerA to ViewControllerB

Step 1. Create Segue from ViewControllerA to ViewControllerB and give Identifier = showDetailSegue in Storyboard as shown below

Step 2. In ViewControllerB Declare a viable named isSomethingEnabled and print its value.

Step 3. In ViewControllerA pass isSomethingEnabled's value while passing Segue

So here is the complete code for:

ViewControllerA

import UIKit

class ViewControllerA: UIViewController  {

    override func viewDidLoad() {
        super.viewDidLoad()
    }

    // MARK:  - - Passing Data through Segue  - -
    @IBAction func goToViewControllerBUsingSegue(_ sender: Any) {
        performSegue(withIdentifier: "showDetailSegue", sender: nil)
    }

    // Segue Delegate Method
    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        if (segue.identifier == "showDetailSegue") {
            let controller = segue.destination as? ViewControllerB
            controller?.isSomethingEnabled = true//passing data
        }
    }
}

ViewControllerB

import UIKit

class ViewControllerB: UIViewController {
    var isSomethingEnabled = false

    override func viewDidLoad() {
        super.viewDidLoad()
        // Print value received through segue
        print("Value of 'isSomethingEnabled' from ViewControllerA: ", isSomethingEnabled)
    }
}

---

Passing Data through Delegate: From ViewControllerB to ViewControllerA

Step 1. Declare Protocol ViewControllerBDelegate in the ViewControllerB file, but outside the class

protocol ViewControllerBDelegate: NSObjectProtocol {

    // Classes that adopt this protocol MUST define
    // this method -- and hopefully do something in
    // that definition.
    func addItemViewController(_ controller: ViewControllerB?, didFinishEnteringItem item: String?)
}

Step 2. Declare Delegate variable instance in ViewControllerB

var delegate: ViewControllerBDelegate?

Step 3. Send data for delegate inside viewDidLoad method of ViewControllerB

delegate?.addItemViewController(self, didFinishEnteringItem: "Data for ViewControllerA")

Step 4. Confirm ViewControllerBDelegate in ViewControllerA

class ViewControllerA: UIViewController, ViewControllerBDelegate  {
// to do
}

Step 5. Confirm that you will implement a delegate in ViewControllerA

if let viewControllerB = UIStoryboard(name: "Main", bundle: nil).instantiateViewController(withIdentifier: "ViewControllerB") as? ViewControllerB {
    viewControllerB.delegate = self//confirming delegate
    if let navigator = navigationController {
        navigator.pushViewController(viewControllerB, animated: true)
    }
}

Step 6. Implement delegate method for receiving data in ViewControllerA

func addItemViewController(_ controller: ViewControllerB?, didFinishEnteringItem item: String?) {
    print("Value from ViewControllerB's Delegate", item!)
}

So here is the complete code for:

ViewControllerA

import UIKit

class ViewControllerA: UIViewController, ViewControllerBDelegate  {

    override func viewDidLoad() {
        super.viewDidLoad()
    }

    // Delegate method
    func addItemViewController(_ controller: ViewControllerB?, didFinishEnteringItem item: String?) {
        print("Value from ViewControllerB's Delegate", item!)
    }

    @IBAction func goToViewControllerForDelegate(_ sender: Any) {

        if let viewControllerB = UIStoryboard(name: "Main", bundle: nil).instantiateViewController(withIdentifier: "ViewControllerB") as? ViewControllerB {
            viewControllerB.delegate = self
            if let navigator = navigationController {
                navigator.pushViewController(viewControllerB, animated: true)
            }
        }
    }
}

ViewControllerB

import UIKit

//Protocol decleare
protocol ViewControllerBDelegate: NSObjectProtocol {
    // Classes that adopt this protocol MUST define
    // this method -- and hopefully do something in
    // that definition.
    func addItemViewController(_ controller: ViewControllerB?, didFinishEnteringItem item: String?)
}

class ViewControllerB: UIViewController {
    var delegate: ViewControllerBDelegate?

    override func viewDidLoad() {
        super.viewDidLoad()
        // MARK:  - - - -  Set Data for Passing Data through Delegate  - - - - - -
        delegate?.addItemViewController(self, didFinishEnteringItem: "Data for ViewControllerA")
    }
}

---

Passing Data through Notification Observer: From ViewControllerB to ViewControllerA

Step 1. Set and post data in the notification observer in ViewControllerB

let objToBeSent = "Test Message from Notification"
        NotificationCenter.default.post(name: Notification.Name("NotificationIdentifier"), object: objToBeSent)

Step 2. Add Notification Observer in ViewControllerA

NotificationCenter.default.addObserver(self, selector: #selector(self.methodOfReceivedNotification(notification:)), name: Notification.Name("NotificationIdentifier"), object: nil)

Step 3. Receive Notification data value in ViewControllerA

@objc func methodOfReceivedNotification(notification: Notification) {
    print("Value of notification: ", notification.object ?? "")
}

So here is the complete code for:

ViewControllerA

import UIKit

class ViewControllerA: UIViewController{

    override func viewDidLoad() {
        super.viewDidLoad()

        // Add observer in controller(s) where you want to receive data
        NotificationCenter.default.addObserver(self, selector: #selector(self.methodOfReceivedNotification(notification:)), name: Notification.Name("NotificationIdentifier"), object: nil)
    }

    // MARK: Method for receiving Data through Post Notification
    @objc func methodOfReceivedNotification(notification: Notification) {
        print("Value of notification: ", notification.object ?? "")
    }
}

ViewControllerB

import UIKit

class ViewControllerB: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        // MARK:Set data for Passing Data through Post Notification
        let objToBeSent = "Test Message from Notification"
        NotificationCenter.default.post(name: Notification.Name("NotificationIdentifier"), object: objToBeSent)
    }
}

---

Passing Data through Block: From ViewControllerB to ViewControllerA

Step 1. Declare block in ViewControllerB

var authorizationCompletionBlock:((Bool)->())? = {_ in}

Step 2. Set data in block in ViewControllerB

if authorizationCompletionBlock != nil
{
    authorizationCompletionBlock!(true)
}

Step 3. Receive block data in ViewControllerA

// Receiver Block
controller!.authorizationCompletionBlock = { isGranted in
    print("Data received from Block is: ", isGranted)
}

So here is the complete code for:

ViewControllerA

import UIKit

class ViewControllerA: UIViewController  {

    override func viewDidLoad() {
        super.viewDidLoad()
    }

    // MARK:Method for receiving Data through Block
    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        if (segue.identifier == "showDetailSegue") {
            let controller = segue.destination as? ViewControllerB
            controller?.isSomethingEnabled = true

            // Receiver Block
            controller!.authorizationCompletionBlock = { isGranted in
                print("Data received from Block is: ", isGranted)
            }
        }
    }
}

ViewControllerB

import UIKit

class ViewControllerB: UIViewController {

    // MARK: Variable for Passing Data through Block
    var authorizationCompletionBlock:((Bool)->())? = {_ in}

    override func viewDidLoad() {
        super.viewDidLoad()

        // MARK: Set data for Passing Data through Block
        if authorizationCompletionBlock != nil
        {
            authorizationCompletionBlock!(true)
        }
    }
}

You can find complete sample Application at my GitHub Please let me know if you have any question(s) on this.

Answer 12

If you want to pass data from one controller to other, try this code:

File FirstViewController.h

@property (nonatomic, retain) NSString *str;

SecondViewController.h

@property (nonatomic, retain) NSString *str1;

File FirstViewController.m

- (void)viewDidLoad
   {
     // Message for the second SecondViewController
     self.str = @"text message";

     [super viewDidLoad];
   }

-(IBAction)ButtonClicked
 {
   SecondViewController *secondViewController = [[SecondViewController alloc] initWithNibName:@"SecondViewController" bundle:nil];
   secondViewController.str1 = str;
  [self.navigationController pushViewController:secondViewController animated:YES];
 }

Answer 13

This is a very old answer and this is anti pattern. Please use delegates. Do not use this approach!!

1. Create the instance of the first view controller in the second view controller and make its property @property (nonatomic,assign).

2. Assign the SecondviewController instance of this view controller.

2. When you finish the selection operation, copy the array to the first View Controller. When you unload the second view, the first view will hold the array data.

Answer 14

I was searching this solution for long time, and at last I found it. First of all, declare all the objects in your SecondViewController.h file like

@interface SecondViewController: UIviewController
{
    NSMutableArray *myAray;
    CustomObject *object;
}

Now in your implementation file, allocate the memory for those objects like this:

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
     self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
     if (self)
     {
         // Custom initialization
         myAray=[[NSMutableArray alloc] init];
         object=[[CustomObject alloc] init];
     }
     return self;
}

Now you have allocated the memory for Array and object. Now you can fill that memory before pushing this ViewController.

Go to your SecondViewController.h and write two methods:

-(void)setMyArray:(NSArray *)_myArray;
-(void)setMyObject:(CustomObject *)_myObject;

In the implementation file, you can implement the function:

-(void)setMyArray:(NSArray *)_myArray
{
     [myArra addObjectsFromArray:_myArray];
}

-(void)setMyObject:(CustomObject *)_myObject
{
     [object setCustomObject:_myObject];
}

Expecting that your CustomObject must have a setter function with it.

Now your basic work is done. Go to the place where you want to push the SecondViewController and do the following stuff:

SecondViewController *secondView= [[SecondViewController alloc] initWithNibName:@"SecondViewController " bundle:[NSBundle MainBundle]] ;
[secondView setMyArray:ArrayToPass];
[secondView setMyObject:objectToPass];
[self.navigationController pushViewController:secondView animated:YES ];

Take care for spelling mistakes.

Answer 15

This is not the way to do it. You should use delegates.

I'll assume we have two view controllers, ViewController1 and ViewController2, and this check thing is in the first one and when its state changes, you want to do something in ViewController2. To achieve that in the proper way, you should do the below:

Add a new file to your project (Objective-C Protocol) menu File → New. Now name it ViewController1Delegate or whatever you want and write these between the @interface and @end directives:

@optional

- (void)checkStateDidChange:(BOOL)checked;

Now go to ViewController2.h and add:

#import "ViewController1Delegate.h"

Then change its definition to:

@interface ViewController2: UIViewController<ViewController1Delegate>

Now go to ViewController2.m and inside the implementation add:

- (void)checkStateDidChange:(BOOL)checked {
     if (checked) {
           // Do whatever you want here
           NSLog(@"Checked");
     }
     else {
           // Also do whatever you want here
           NSLog(@"Not checked");
     }
}

Now go to ViewController1.h and add the following property:

@property (weak, nonatomic) id<ViewController1Delegate> delegate;

Now if you are creating ViewController1 inside ViewController2 after some event, then you should do it this way using NIB files:

ViewController1* controller = [[NSBundle mainBundle] loadNibNamed:@"ViewController1" owner:self options:nil][0];
controller.delegate = self;
[self presentViewController:controller animated:YES completion:nil];

Now you are all set. Whenever you detect the event of check changed in ViewController1, all you have to do is the below:

[delegate checkStateDidChange:checked]; // You pass here YES or NO based on the check state of your control

Answer 16

If you want to send data from one to another viewController, here's a way to do it:

Say we have viewControllers: viewControllerA and viewControllerB

Now in file viewControllerB.h

@interface viewControllerB : UIViewController {

  NSString *string;
  NSArray *array;

}

- (id)initWithArray:(NSArray)a andString:(NSString)s;

In file viewControllerB.m:

#import "viewControllerB.h"

@implementation viewControllerB

- (id)initWithArray:(NSArray)a andString:(NSString)s {

   array = [[NSArray alloc] init];
   array = a;

   string = [[NSString alloc] init];
   string = s;

}

In file viewControllerA.m:

#import "viewControllerA.h"
#import "viewControllerB.h"

@implementation viewControllerA

- (void)someMethod {

  someArray = [NSArray arrayWithObjects:@"One", @"Two", @"Three", nil];
  someString = [NSString stringWithFormat:@"Hahahahaha"];

  viewControllerB *vc = [[viewControllerB alloc] initWithArray:someArray andString:someString];

  [self.navigationController pushViewController:vc animated:YES];
  [vc release];
}

So this is how you can pass data from viewControllerA to viewControllerB without setting any delegate. ;)

Answer 17

With a Swift slant and want a bare-bones example, here is my go-to method for passing data if you are using a segue to get around.

It is similar to the above but without the buttons, labels and such. Just simply passing data from one view to the next.

Setup The Storyboard

There are three parts.

1. The Sender
2. The Segue
3. The Receiver

This is a very simple view layout with a segue between them.

---

---

Here is the setup for the sender

---

---

Here is the setup for the receiver.

---

---

Lastly, the setup for the segue.

---

---

The View Controllers

We are keeping this simple so no buttons and not actions. We are simply moving data from the sender to the receiver when the application loads and then outputting the transmitted value to the console.

This page takes the initially loaded value and passes it along.

import UIKit


class ViewControllerSender: UIViewController {

    // THE STUFF - put some information into a variable
    let favoriteMovie = "Ghost Busters"

    override func viewDidAppear(animated: Bool) {
        // PASS IDENTIFIER - go to the receiving view controller.
        self.performSegueWithIdentifier("goToReciever", sender: self)
    }

    override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {

        // GET REFERENCE - ...to the receiver view.
        var viewControllerReceiver = segue.destinationViewController as? ViewControllerReceiver

        // PASS STUFF - pass the variable along to the target.
        viewControllerReceiver!.yourFavMovie = self.favoriteMovie

    }
}

This page just sends the value of the variable to the console when it loads. By this point, our favorite movie should be in that variable.

import UIKit

class ViewControllerReceiver: UIViewController {

    // Basic empty variable waiting for you to pass in your fantastic favorite movie.
    var yourFavMovie = ""

    override func viewDidLoad() {
        super.viewDidLoad()

        // And now we can view it in the console.
        println("The Movie is \(self.yourFavMovie)")

    }
}

That is how you can tackle it if you want to use a segue and you don't have your pages under a navigation controller.

Once it is run, it should switch to the receiver view automatically and pass the value from the sender to the receiver, displaying the value in the console.

Answer 18

Passing data between FirstViewController to SecondViewController as below

For example:

FirstViewController String value as

StrFirstValue = @"first";

So we can pass this value in the second class using the below steps:

1. We need to create a string object in the SecondViewController.h file

    NSString *strValue;
   

2. Need to declare a property as the below declaration in the .h file

    @property (strong, nonatomic)  NSString *strSecondValue;
   

3. Need synthesize that value in the FirstViewController.m file below the header declaration

    @synthesize strValue;
   

   And in file FirstViewController.h:

    @property (strong, nonatomic)  NSString *strValue;
   

4. In FirstViewController, from which method we navigate to the second view, please write the below code in that method.

    SecondViewController *secondView= [[SecondViewController alloc]
    initWithNibName:@"SecondViewController " bundle:[NSBundle MainBundle]];
   
    [secondView setStrSecondValue:StrFirstValue];
   
    [self.navigationController pushViewController:secondView animated:YES ];
   

Answer 19

In my case, I used a singleton class which could work as a global object allowing accesses to the data from almost everywhere in the app.

The first thing is to build a singleton class. Please refer to the page What should my Objective-C singleton look like?.

And to make the object globally accessible, I simply imported it in appName_Prefix.pch which was for applying import statement in every classes.

To access this object and to use it, I simply implemented a class method to return the shared instance, which contains its own variables.

Answer 20

I am currently contributing to an open source solution to this problem through a project called MCViewFactory, which may be found here:

Manticore iOS View Factory

The idea is imitate Android's intent paradigm, using a global factory to manage which view you are looking at and using "intents" to switch and pass data between views. All the documentation is on the GitHub page, but here are some highlights:

You setup all your views in .XIB files and register them in the app delegate, while initializing the factory.

// Register activities

MCViewFactory *factory = [MCViewFactory sharedFactory];

// The following two lines are optional.
[factory registerView:@"YourSectionViewController"];

Now, in your view controller (VC), anytime you want to move to a new VC and pass data, you create a new intent and add data to its dictionary (savedInstanceState). Then, just set the current intent of factory:

MCIntent* intent = [MCIntent intentWithSectionName:@"YourSectionViewController"];
[intent setAnimationStyle:UIViewAnimationOptionTransitionFlipFromLeft];
[[intent savedInstanceState] setObject:@"someValue" forKey:@"yourKey"];
[[intent savedInstanceState] setObject:@"anotherValue" forKey:@"anotherKey"];
// ...
[[MCViewModel sharedModel] setCurrentSection:intent];

All of your views that conform to this need to be subclasses of MCViewController, which allow you to override the new onResume: method, allowing you access to the data you've passed in.

-(void)onResume:(MCIntent *)intent {
    NSObject* someValue = [intent.savedInstanceState objectForKey:@"yourKey"];
    NSObject* anotherValue = [intent.savedInstanceState objectForKey:@"anotherKey"];

    // ...

    // Ensure the following line is called, especially for MCSectionViewController
    [super onResume:intent];
}

Answer 21

Create the property in the next view controller .h file and define getters and setters.

Add this property in NextVC.h on nextVC:

@property (strong, nonatomic) NSString *indexNumber;

Add

@synthesize indexNumber; in NextVC.m

And last

NextVC *vc = [[NextVC alloc]init];

vc.indexNumber = @"123";

[self.navigationController vc animated:YES];

Answer 22

There are tons of ways to do this and it's important to pick the right one. Probably one of the biggest architectural decisions lies on how the model code will be shared or accessed throughout the app.

I wrote a blog post about this a while back: Sharing Model Code. Here's a brief summary:

Shared data

One approach is to share pointers to the model objects between view controllers.

• Brute force iteration on view controllers (in Navigation or Tab Bar Controller) to set the data
• Set data in prepareForSegue (if storyboards) or init (if programmatic)

Since prepare for segue is the most common here is an example:

override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
    var next = segue.destinationViewController as NextViewController
    next.dataSource = dataSource
}

Independent access

Another approach is to handle a screen full of data at a time and instead of coupling the view controllers to each other couple each view controller to single data source that they can get to independently.

The most common way I've seen this done is a singleton instance. So if your singleton object was DataAccess you could do the following in the viewDidLoad method of UIViewController:

func viewDidLoad() {
    super.viewDidLoad()
    var data = dataAccess.requestData()
}

There are addition tools that also help pass along data:

• Key-Value Observing
• NSNotification
• Core Data
• NSFetchedResultsController
• Data Source

Core Data

The nice thing about Core Data is that it has inverse relationships. So if you want to just give a NotesViewController the notes object you can because it'll have an inverse relationship to something else like the notebook. If you need data on the notebook in the NotesViewController you can walk back up the object graph by doing the following:

let notebookName = note.notebook.name

Read more about this in my blog post: Sharing Model Code

Answer 23

If you want to pass data from ViewControlerOne to ViewControllerTwo, try these...

Do these in ViewControlerOne.h:

 @property (nonatomic, strong) NSString *str1;

Do these in ViewControllerTwo.h:

 @property (nonatomic, strong) NSString *str2;

Synthesize str2 in ViewControllerTwo.m:

@interface ViewControllerTwo ()
@end
@implementation ViewControllerTwo
@synthesize str2;

Do these in ViewControlerOne.m:

 - (void)viewDidLoad
 {
   [super viewDidLoad];

   // Data or string you wants to pass in ViewControllerTwo...
   self.str1 = @"hello world";
 }

O the buttons click event, do this:

-(IBAction)ButtonClicked
{
  // Navigation on buttons click event from ViewControlerOne to ViewControlerTwo with transferring data or string..
  ViewControllerTwo *objViewTwo = [self.storyboard instantiateViewControllerWithIdentifier:@"ViewControllerTwo"];
  obj.str2 = str1;
  [self.navigationController pushViewController: objViewTwo animated:YES];
}

Do these in ViewControllerTwo.m:

- (void)viewDidLoad
{
  [super viewDidLoad];
  NSLog(@"%@", str2);
}

Answer 24

You can save data in an App delegate to access it across view controllers in your application. All you have to do is create a shared instance of an app delegate:

AppDelegate *appDelegate = (AppDelegate *)[UIApplication sharedApplication].delegate;

For Example

If you declare a NSArray object *arrayXYZ, then you can access it in any view controller by appDelegate.arrayXYZ.

Answer 25

Delegation is the only one solution to perform such operations when you are using .xib files. However, all previous answers are for storyboard for .xibs files. You need to use delegation. That's the only solution you can use.

Another solution is use the singleton class pattern. Initialize it once and use it in your entire app.

Answer 26

NewsViewController

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
  [tbl_View deselectRowAtIndexPath:indexPath animated:YES];
  News *newsObj = [newstitleArr objectAtIndex:indexPath.row];
  NewsDetailViewController *newsDetailView = [[NewsDetailViewController alloc] initWithNibName:@"NewsDetailViewController" bundle:nil];

  newsDetailView.newsHeadlineStr = newsObj.newsHeadline;

  [self.navigationController pushViewController:newsDetailView animated:YES];
}

NewsDetailViewController.h

@interface NewsDetailViewController : UIViewController
@property(nonatomic,retain) NSString *newsHeadlineStr;
@end

NewsDetailViewController.m

@synthesize newsHeadlineStr;

Answer 27

For SwiftUI

Think of @EnvironmentObject as a smarter, simpler way of using @ObservedObject on lots of views. Rather than creating some data in view A, then passing it to view B, then view C, then view D before finally using it, you can create it in view and put it into the environment so that views B, C, and D will automatically have access to it.

Note: Environment objects must be supplied by an ancestor view – if SwiftUI can’t find an environment object of the correct type you’ll get a crash. This applies for previews too, so be careful.

As an example, here’s an observable object that stores user settings:

class UserSettings: ObservableObject {
     @Published var score = 0
}

Answer 28

I like the idea of model objects and mock objects based on NSProxy to commit or discard data if what the user selects can be cancelled.

It's easy to pass data around since it's a single object or couple of objects and if you have, let's say, a UINavigationController controller, you can keep the reference to the model inside and all pushed view controllers can access it directly from the navigation controller.

Answer 29

I have seen a lot of people over complicating this using the didSelectRowAtPath method. I am using Core Data in my example.

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath{

    // This solution is for using Core Data
    YourCDEntityName * value = (YourCDEntityName *)[[self fetchedResultsController] objectAtIndexPath: indexPath];

    YourSecondViewController * details = [self.storyboard instantiateViewControllerWithIdentifier:@"nameOfYourSecondVC"]; // Make sure in storyboards you give your second VC an identifier

    // Make sure you declare your value in the second view controller
    details.selectedValue = value;

    // Now that you have said to pass value all you need to do is change views
    [self.navigationController pushViewController: details animated:YES];

}

Four lines of code inside the method and you are done.

Answer 30

There are 3 types for passing data one ViewController to another ViewController.

1. Programatically
2. Segue
3. UserDefaults

Demo Project Link Here - https://github.com/kamanijasmin13/Swift-Pass-data-between-viewcontrollers

Programatically

Segue

UserDefaults

Demo Project Link Here - https://github.com/kamanijasmin13/Swift-Pass-data-between-viewcontrollers

Answer 31

There are many answers to this questions offering many different ways to perform view controller communication that would indeed work, but I don't see anywhere mentioned which one are actually best to use and which ones to avoid.

In practice, in my opinion only a few solutions are recommended:

• To pass data forward:
  • override the prepare(for:sender:) method of UIViewController when using a storyboard and segues
  • pass data through an initializer or through properties when performing view controller transitions thtough code
• To pass data backwards
  • update the app shared state (which you can pass forward between view controllers with either one of the methods above)
  • use delegation
  • use an unwind segue

Solutions I recommend NOT to use:

• Referencing the previous controller directly instead of using delegation
• Sharing data through a singleton
• Passing data through the app delegate
• Sharing data through the user defaults
• Passing data through notifications

These solutions, although working in the short term, introduce too many dependencies that will garble the architecture of the app and create more problems later.

For those interested, I wrote some articles that address these points more in depth and highlight the various drawbacks:

• How iOS View Controllers Communicate With Each Other
• How to Structure the Code of iOS Apps
• Understanding the Core Architectural Principles of iOS Development with a Practical Example

Answer 32

Using Notification Center

For Swift 3

let imageDataDict:[String: UIImage] = ["image": image]

// Post a notification
NotificationCenter.default.post(name: NSNotification.Name(rawValue: "notificationName"), object: nil, userInfo: imageDataDict)
// `default` is now a property, not a method call

// Register to receive notification in your class
NotificationCenter.default.addObserver(self, selector: #selector(self.showSpinningWheel(_:)), name: NSNotification.Name(rawValue: "notificationName"), object: nil)

// Handle notification
func showSpinningWheel(_ notification: NSNotification) {
    print(notification.userInfo ?? "")
    if let dict = notification.userInfo as NSDictionary? {
        if let id = dict["image"] as? UIImage {
            // Do something with your image
        }
    }
}

For Swift 4

let imageDataDict:[String: UIImage] = ["image": image]

// Post a notification
NotificationCenter.default.post(name: NSNotification.Name(rawValue: "notificationName"), object: nil, userInfo: imageDataDict)
// `default` is now a property, not a method call

// Register to receive notification in your class
NotificationCenter.default.addObserver(self, selector: #selector(self.showSpinningWheel(_:)), name: NSNotification.Name(rawValue: "notificationName"), object: nil)

// Handle notification
@objc func showSpinningWheel(_ notification: NSNotification) {
    print(notification.userInfo ?? "")
    if let dict = notification.userInfo as NSDictionary? {
        if let id = dict["image"] as? UIImage {
            // Do something with your image
        }
    }
}

Answer 33

There are several ways to pass data between view controllers.

1. Delegate protocol (Backward direction).
2. NSNotification center (Both Direction).
3. UserDefault (Both Direction).
4. Direct Property (Forward Direction).
5. Closure (Backward Direction).
6. Segue (Forward Direction).

Answer 34

You can create a push segue from the source viewcontroller to the destination viewcontroller and give an identifier name like below.

You have to perform a segue from didselectRowAt like this.

func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
    performSegue(withIdentifier: "segue", sender: self)
}

And you can pass the array of the selected item from the below function.

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    let index = CategorytableView.indexPathForSelectedRow
    let indexNumber = index?.row
    print(indexNumber!)
    let VC = segue.destination as! AddTransactionVC
    VC.val = CategoryData[indexNumber!] . // Here you can pass the entire array instead of an array element.
}

And you have to check the value in viewdidload of destination viewcontroller and then store it into the database.

override func viewDidLoad{
    if val != ""{
        btnSelectCategory.setTitle(val, for: .normal)
    }
}

Answer 35

Pure Combine solution for UIKit and AppKit

Let's take a simple example of passing an Int value of count between ViewControllers.

A parent ViewController (VC) has a variable named count, and child ViewController can let the user change the value of count. Once the user is done changing the value, they will dismiss the child controller and parent VC should have the updated value after that.

---

Parent View Controller

ParentVC gets the updated value of count from the ChildVC

class ParentVC: UIViewController {
    var count = 1
    var countObserver: AnyCancellable! // 1

    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        let childVC = segue.destination as! ChildVC
        childVC.sliderValue = count // 2
        countObserver = childVC.$sliderValue // 3
            .assign(to: \.count, on: self)
    }
}

1. countObserver will retain the observer that would observe changes made by ChildVC

2. When the child appears, we assign the current count value from parent to a control (here UISlider) in the ChildVC, which becomes a starting point for modifying the value of count.

3. We observe sliderValue (which is a publisher) that would emit the value of count that the user would change by dragging the slider. Note that we used $sliderValue instead of just sliderValue.

---

Child View Controller

ChildVC is the one that would emit values that ParentVC is interested in:

class ChildVC: UIViewController {
    @Published var sliderValue: Int = 0 // 1

    @IBOutlet var sliderOutlet: UISlider!

    @IBAction func slided(_ sender: UISlider) {
        sliderValue = Int(sender.value)
    }
}

1. @Published is Publisher that stores value and emits a signal when the value changes. It behaves just like a regular var but can publish values that can be accessed by prepending $ sign to it.

---

CurrentValueSubject and PassthroughSubject vs @Published

1. CurrentValueSubject can also be used instead of @Published. The only difference is, you would have to manually emit the signal. It is useful in cases where you want to control when to emit. For example, you can emit the value, but only if it falls in a specific range.

2. PassthroughSubject also can be used instead of @Published or CurrentValueSubject. Here, the difference is PassthroughSubject cannot hold a value, it can just emit a signal. This can be useful when the value cannot be concretely represented in a variable.

Answer 36

This is a really great tutorial for anyone that wants one. Here is the example code:

- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
    if ([segue.identifier isEqualToString:@"myIdentifer]) {
        NSIndexPath *indexPath = [self.tableView indexPathForSelectedRow];
        myViewController *destViewController = segue.destinationViewController;
        destViewController.name = [object objectAtIndex:indexPath.row];
    }
}

Answer 37

There are many solutions for passing data in Swift.

Passing data forward

My two favorite ways to pass data forwardly is dependency injection (DI) and Property Observers

Dependency Injection

class CustomView : UIView {
    init(_ with model : Model) {
        // Do what you want with data
    }
}

Property Observers

class CustomView : UIView {
    var model : Model? {
        didSet {
            // Do what you want with data after assign data to model
        }
        willSet {
            // Do what you want with data before assign data to model
        }
    }
}

Passing data backward

Also favorite ways to passing data to the previous VC/view:

Protocol and Delegate

protocol CustomViewDelegate : class {
    func addItemViewController(_ with data: Model?)
}

weak var delegate : CustomViewDelegate?

class AnotherCustomView: UIView {

     let customView = AnotherCustomView()

     init() {
         customView.delegate = self
     }
}

extention AnotherCustomView : CustomViewDelegate {
    func addItemViewController(_ with data: Model?) {
        // Do what you want with data
    }
}

Closure

class AnotherCustomView : UIView {
     init(addItem: @escaping (_ value : Model?) -> ()) {
        // Do what you want with data
     }
}

class CustomView : UIView {

    init() {
        let customView = AnotherCustomView { [weak self] model in
            // Do what you want with data
        }
    }
}

Answer 38

To send the data from one view controller (VC) to the other, use this simple approach:

YourNextVC *nxtScr = (YourNextVC*)[self.storyboard  instantiateViewControllerWithIdentifier:@"YourNextVC"];//Set this identifier from your storyboard

nxtScr.comingFrom = @"PreviousScreen"l
[self.navigationController nxtScr animated:YES];

Answer 39

Well, we have a few ways we can work with the delegates system or using storyboardSegue:

1. As working with setter and getter methods, like in viewController.h

    @property (retain, nonatomic) NSString *str;
   

   Now, in viewController.m

   @synthesize str;
   

   Here I have a PDF URL and a segue to another viewController like this and pdfObject is my pdfModel. It is basically an NSOBJECT class.

    str = [NSString stringWithFormat:@"%@", pdfObject.objPath];
    NSLog(@"pdfUrl :***: %@ :***:", pdfUrl);
   
    [self performSegueWithIdentifier:@"programPDFViewController_segue" sender:self];
   
    #pragma mark - Navigation
   
    // In a storyboard-based application, you will often want to do a little preparation before navigation
   
    - (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
   
         if ([[segue identifier] isEqualToString:@"programPDFViewController_segue"]) {
             programPDFViewController *pdfVC = [segue destinationViewController];
             [pdfVC setRecievedPdfUrl:str];
         }
    }
   

   Now successfully I received my PDF URL string and other ViewController and use that string in webview...

2. As working with delegates like this I have one NSObject class of utilities containing my methods of dateFormatter, sharedInstance, EscapeWhiteSpaceCharacters, convertImageToGrayScale and more method I worked with throughout the application so now in file utilities.h.

   In this, you don’t need to create variables every time parsing data from one to another view controller. One time, you create a string variable in file utilities.h.

   Just make it nil and use it again.

    @interface Utilities : NSObject
   

   File Utilities.h:

    +(Utilities*)sharedInstance;
   
    @property(nonatomic, retain)NSString* strUrl;
   

   Now in file utilities.m:

    @implementation utilities
   
    +(utilities*)sharedInstance
    {
        static utilities* sharedObj = nil;
        if (sharedObj == nil) {
            sharedObj = [[utilities alloc] init];
        }
        return sharedObj;
    }
   

   Now it's done, come to your file firstViewController.m and call the delegate

   NSString*str = [NSString stringWithFormat:@"%@", pdfObject.objPath];

   [Connection sharedInstance].strUrl = nil; [Connection sharedInstance].strUrl = str;

   Now go to you file secondViewController.m directly, and use it without creating a variable

   In viewwillapear what I did:

    -(void)viewWillAppear:(BOOL)animated {
        [super viewWillAppear:YES];
   
        [self webViewMethod:[Connection sharedInstance].strUrl];
    }
   
   
    -(void)WebViewMethod:(NSString)Url {
   
        // Working with webview. Enjoy coding :D
    }
   

This delegate work is reliable with memory management.

Answer 40

An Apple way to do this is to use Segues. You need to use the prepareForSegue() function.

There are lots of great tutorials around, and here is one: Unleash Your Inner App Developer Part 21: Passing Data Between Controllers

Also, read up the Apple documentation on using segues: Using Segues

Answer 41

I recommend blocks/closures and custom constructors.

Suppose you have to pass string from FirstViewController to SecondViewController.

Your First View Controller.

class FirstViewController : UIViewController {

    func moveToViewControllerB() {

        let second_screen = SecondViewController.screen(string: "DATA TO PASS", call_back: {
            [weak self] (updated_data) in
            ///This closure will be called by second view controller when it updates something
        })
        self.navigationController?.pushViewController(second_screen, animated: true)
    }


}

Your Second View Controller

class SecondViewController : UIViewController {

    var incoming_string : String?
    var call_back : ((String) -> Void)?

    class func screen(string: String?, call_back : ((String) -> Void)?) -> SecondViewController {

        let me = SecondViewController(nibName: String(describing: self), bundle: Bundle.main);
        me.incoming_string = string
        me.call_back = call_back
        return me
    }

    // Suppose its called when you have to update FirstViewController with new data.
    func updatedSomething() {

        //Executing block that is implemented/assigned by the FirstViewController.
        self.call_back?("UPDATED DATA")
    }

}

Answer 42

You have to always follow the MVC concept when creating apps for iOS.

There are two scenarios where you may want to pass data from a ViewController to another:

1. When there is an "A" ViewContoller in the hierarchy and you want to send some data to "B" which is the next viewcontroller. In this case you have to use Segue. Just set an identifier for the segue and then in the "A" VC, write the following code:

   override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
       if segue.identifier == "A to B segue identifier" {
           let bViewController = segue.destination as! UIDocumentBrowserViewController
           bViewController.data = someData
       }
   }
   

2. When there is an A which opened B upon itself as modal (or embed). Now the B viewcontroller should be blind about its parent. So the best way to send data back to A is to use Delegation.

   Create a delegate protocol in the B viewcontroller and a delegate property. So B will report (send data back) to it's delegate. In the A viewcontroller, we implement the B viewcontroller's delegate protocol and will set self as the delegate property of B viewcontroller in prepare(forSegue:) method.

This is how it should be implemented correctly.

Answer 43

I prefer to make it without delegates and segues. It can be done with custom init or by setting optional values.

1. Custom init

class ViewControllerA: UIViewController {
  func openViewControllerB() {
    let viewController = ViewControllerB(string: "Blabla", completionClosure: { success in
      print(success)
    })
    navigationController?.pushViewController(animated: true)
  }
}

class ViewControllerB: UIViewController {
  private let completionClosure: ((Bool) -> Void)
  init(string: String, completionClosure: ((Bool) -> Void)) {
    self.completionClosure = completionClosure
    super.init(nibName: nil, bundle: nil)
    title = string
  }

  func finishWork() {
    completionClosure()
  }
}

2. Optional vars

class ViewControllerA: UIViewController {
  func openViewControllerB() {
    let viewController = ViewControllerB()
    viewController.string = "Blabla"
    viewController.completionClosure = { success in
      print(success)
    }
    navigationController?.pushViewController(animated: true)
  }
}

class ViewControllerB: UIViewController {
  var string: String? {
    didSet {
      title = string
    }
  }
  var completionClosure: ((Bool) -> Void)?

  func finishWork() {
    completionClosure?()
  }
}

Answer 44

Use notification center to pass data from one view to another.

The observer listener pattern works the best. The other workaround can be create the same objects in both classes.

Create a class 2 object in class one. Access the data objects to be passed, set them, and then push the view controller.