Data being lost after passing between functions

Question

I am having problem here regarding data lost on NSDictionary (or whatever data type I am trying to pass between view controllers). I am passing the data as I will show on code below. But after passing and then accessing the data again, I received a null object.

FirstViewController.m

-(void)showSecondViewController{
  SecondViewController *secondVC = [SecondViewController new];
  NSMutableDictionary *passedData = [[NSMutableDictionary alloc]init];
  [passedData setObject:@"First Object" forKey:@"first_obj"];
  [passedData setObject:@"Second Object" forKey:@"second_obj"];
  [secondVC setData:passedData];
  [self performSegueWithIdentifier:@"SecondViewControllerSegue" sender:self];
}

In my SecondViewController.h

 @interface SecondViewController : UIViewController
{
   NSDictionary *passedDataContainer;
}

-(void)setData(NSDictionary *)data;

And on SecondViewController.m

-(void)setData(NSDictionary *)data{
   passedDataContainer = data;
}

From this I am assuming that I have my NSDictionary from my FirstViewController, but when I used it, say for example...

-(void)usePassedData{
  NSLog(@"Display Passed Data from FirstViewController: %@",passedDataContainer);
}

In this code snippet, the output will be

Display Passed Data from FirstViewController: (null)

I hope I have explained the case well. I have checked some possible fixes that I found here on SO like for example, this post ---> iOS NSDictionary pass through function. I will be glad if I will know what is the cause of this, I am new to Objective-C.

P.S. I am using ARC.

Thanks.

This tutorial link may help you: http://www.appcoda.com/storyboards-ios-tutorial-pass-data-between-view-controller-with-segue/ — Puneet Sharma, Dec 16 '13 at 06:45

score 0 · Answer 1 · edited May 23 '17 at 10:32

0

If you want to pass the data from secondviewcontroller to first view controller then you can used CUSTOM DELEGATE , using custome delegate you can pass the data from secondviewcintroller to firstviewcontroller.

This link may be helpful to you. This is second link to understand the delegate.

edited May 23 '17 at 10:32

Community

1
1

answered Dec 16 '13 at 06:33

Maulik Kundaliya

452
3
17

score 0 · Answer 2 · answered Dec 16 '13 at 06:33

There are many ways to achieve for your solution.

NSUserDefaults.

Delegates(Custom).

For Your problem :. Use the @PRoperty (Strong) reference to the NSDictionary and refer it from FirstViewController with the proper alloc of instance of SecondViewController.

Shankar BS · Accepted Answer · 2013-12-16T07:24:35.283

try like this, hope this helps u :)

in your SecondViewController.h

 @interface SecondViewController : UIViewController
 {
   NSDictionary *passedDataContainer;
 }

@property (nonatomic, retain) NSDictionary *data;

and in SecondViewController.m

   @synthesize data; //just synthesize it

and your FirstViewController.m

-(void)showSecondViewController{
 SecondViewController *secondVC = [SecondViewController new];
 NSMutableDictionary *passedData = [[NSMutableDictionary alloc]init];
 [passedData setObject:@"First Object" forKey:@"first_obj"];
 [passedData setObject:@"Second Object" forKey:@"second_obj"];
  secondVC.data = passedData; //[secondVC setData:passedData];//change this
 [self performSegueWithIdentifier:@"SecondViewControllerSegue" sender:self];
}

Suhit Patil · Answer 4 · 2013-12-16T06:51:54.820

Form your explanation, you are using storyboard segue to transition from FirstViewController to SecondViewController. You need to pass data in prepareForSegue method instead of showSecondViewController method.

try this

FirstViewController.m

-(void)showSecondViewController{

  [self performSegueWithIdentifier:@"SecondViewControllerSegue" sender:self];
}

- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
     if ([segue.identifier isEqualToString:@"SecondViewControllerSegue"]){
     NSMutableDictionary *passedData = [[NSMutableDictionary alloc]init];
     [passedData setObject:@"First Object" forKey:@"first_obj"];
     [passedData setObject:@"Second Object" forKey:@"second_obj"];

     SecondViewController *secondVC = (SecondViewController *)segue.destinationViewController;
    [secondVC setData:passedData];
}

In SecondViewController.h

@property(strong, nonatomic) NSDictionary *data;

In SecondViewController.m

-(void)usePassedData{
  NSLog(@"Display Passed Data from FirstViewController: %@",data);
}

Data being lost after passing between functions

4 Answers4