iOS - UIButton event crash

Question

I tried the codes of Moshe in this link, and it worked except the part of "for (UIButton *button in ..." and it crashes every time when I click on a button.

So I tried this code in the viewDidLoad method:

UIButton *testButton = [[UIButton alloc]initWithFrame:CGRectMake(20,50,30,30)];
    testButton.backgroundColor = [UIColor orangeColor];
    [testButton setTitleColor:[UIColor blackColor] forState:UIControlStateNormal];
    [testButton setTitle:@"A" forState:UIControlStateNormal];
    [testButton addTarget:self action:@selector(commonMethodForButtons:) forControlEvents:UIControlEventTouchDown];

    [self.view addSubview:testButton];
    [testButton release];

My project contains nothing than this and Moshe´s sample codes. Any idea why the app crashes? I get no crash log.

EDIT:

in the open scope I have this method:

-(void)commonMethodForButtons:(id)sender
{
    NSLog (@"you touched me!");
}

EDIT 2:

I found the reason to this problem:

I commented out [mvc release]; in AppDelegate, so it works perfectly now :)

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {    

    // Override point for customization after application launch.

    MVC *mcv = [[MVC alloc]initWithNibName:nil bundle:nil];

    [self.window addSubview: mcv.view];

    //[mcv release];

    [self.window makeKeyAndVisible];

    return YES;
}

Thank you for pointing this out! :)

@vladimir I have added the code in the edit. this method was there before you asked. — wagashi, Jul 21 '12 at 21:12
try to set exception breakpoint or check console for error messages may be... your code looks fine so far. — Vladimir, Jul 21 '12 at 21:16
Your code works perfectly for me. Is the `commonMethodForButtons:` implemented in your ViewController? — Adam, Jul 21 '12 at 21:18
are u sure there is no typo issue in the name of the method? - usually the crash occurs when you the method you mentioned in the selector can't be found... — tiguero, Jul 21 '12 at 21:27
@adam yes the method is implemented in the .h file. Like Moshe`s sample code. — wagashi, Jul 21 '12 at 21:30
@wagashi Methods should be implemented in `.m`. You can declare it in `.h`, but in this case there is no need for that. — Adam, Jul 21 '12 at 21:32
Does anything retain this view controller that handles the button touch? — Phillip Mills, Jul 21 '12 at 21:33
@wagashi That makes sense but you now technically have a leak because once that method is finished you have no way of releasing `mcv`. In this case, it may not matter but it's good to get into the habit of accessing things as properties that you need to use later. — Phillip Mills, Jul 21 '12 at 21:40
ARC stands for auto reference counting. Basically it tells your compiler where to add automatically the retain and release method so you don't have to worry about this. Check this: http://stackoverflow.com/questions/6368600/some-questions-about-automatic-reference-counting-in-ios5-sdk — tiguero, Jul 21 '12 at 21:40
@tiguero Ah, right, I have read about this before. No, I do not have ARC in this project. — wagashi, Jul 21 '12 at 21:48
In Xcode go to Product > Analyze and you probably will have a leak before the line you commented out — Teofilo Israel Vizcaino Rodrig, Jul 22 '12 at 05:25
@Teofilo you are right, but how do I solve this? Philip mentioned that I should make mcv a property...but I don`t know how. — wagashi, Jul 22 '12 at 06:20
In the header file of the AppDelegate: @ interface AppDelegate : UIResponder { MVC *mcv; } @ property (strong, nonatomic) MVC *mcv; In the implementation file @implementation AppDelegate @ synthesize mcv; - (void)dealloc { [mcv release]; [super dealloc]; } — Teofilo Israel Vizcaino Rodrig, Jul 22 '12 at 12:24
@teofile thanks. Could you post your own post, so I can accept your answer? — wagashi, Jul 22 '12 at 12:41
-1 You should not rely on your not releasing of the controller in `didFinishLaunchingWithOptions`. If you ever converted to ARC (which you should) this would crash again. You should (a) not be adding mcv.view as a subview, but rather (b) set `self.window.rootViewController = mcv` and restore your `release` statement that you commented out. — Rob, Jul 24 '12 at 15:22

score 1 · Accepted Answer · edited Jul 23 '12 at 11:40

1

Use mcv as property

In the header file of the AppDelegate:

@class MVC;
    @interface AppDelegate : UIResponder {
    MVC *mcv;
}

@property (nonatomic, retain) MVC *mcv;

In the implementation file

@implementation AppDelegate

@synthesize mcv;

- (void)dealloc
{
    [mcv release];
    [super dealloc];
}

edited Jul 23 '12 at 11:40

wagashi

894
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15
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answered Jul 22 '12 at 13:08

Teofilo Israel Vizcaino Rodrig

1,480
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Um, I get warning in the header file: `error: expected specifier-qualifier-list before 'MVC'` I have @interface xxxAppDelegate : NSObject { ... – wagashi Jul 22 '12 at 13:34
1

@teofile I found the solution. Please take a look at this http://stackoverflow.com/questions/7428706/error-expected-specifier-qualifier-list-before-xxx I get this warning because it is cyclical dependencies. I added `@class MVC;` in front of `@interface AppDelegate ...` in the header file. – wagashi Jul 23 '12 at 11:23

Rob · Answer 2 · 2012-07-24T16:01:55.167

No, you should not be solving your problem by commenting out the [mcv release] (which is only fixing a symptom, not the problem, and will cause problems if you ever convert to ARC, which you should) nor should you, as in the currently accepted answer, be storing mcv (shouldn't that be mvc?) as an ivar of the app delegate but (a) failing to set rootViewController but (b) still using addSubview. You should use the app delegate's rootViewController. The current solutions will not configure your view controller hierarchy correctly. It should be as follows:

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {    

    // Override point for customization after application launch.

    MVC *mvc = [[MVC alloc]initWithNibName:nil bundle:nil]; // really no NIB name?!?

    //[self.window addSubview: mvc.view];
    self.window.rootViewController = mvc;

    [mvc release];

    [self.window makeKeyAndVisible];

    return YES;
}

Or, better, conform to the standard didFinishLaunchingWithOptions generated by the non-ARC Xcode templates, e.g.:

//  AppDelegate.h

#import <UIKit/UIKit.h>

@class ViewController;

@interface AppDelegate : UIResponder <UIApplicationDelegate>

@property (strong, nonatomic) UIWindow *window;
@property (strong, nonatomic) ViewController *viewController;

@end

And

//  AppDelegate.m

#import "AppDelegate.h"

#import "MVC.h"

@implementation AppDelegate

@synthesize window = _window;
@synthesize viewController = _viewController;

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {    

    // Override point for customization after application launch.

    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    self.viewController = [[MVC alloc]initWithNibName:nil bundle:nil]; // really no NIB name?!?
    self.window.rootViewController = self.viewController;
    [self.window makeKeyAndVisible];

    return YES;
}

I've never had to refer to this viewController property, but given that this is the default code that Xcode generates, I assume it is good practice.

iOS - UIButton event crash

2 Answers2