ios : Nullpointer exception - ios

Question

I got the following code:
- (void) hide_waiting_activity
{
[UIView beginAnimations:nil context:NULL]; {
[UIView setAnimationCurve:UIViewAnimationCurveEaseInOut];
[UIView setAnimationDuration:.5];
self.waiting_view.alpha = 0;
self.waiting_label.alpha = 0;
self.activity_indicator.alpha = 0;
} [UIView commitAnimations];
}
The problem: It crashes sometimes and sometimes not. If it crashes the console output looks something like this:
2013-02-07 18:16:21.658 driver[5912:907]
-[NSISRestrictedToNonNegativeVariable count]: unrecognized selector sent to instance 0x1dd3aea0 2013-02-07 18:16:21.679 driver[5912:907]
* Terminating app due to uncaught exception 'NSInvalidArgumentException', reason:
'-[NSISRestrictedToNonNegativeVariable count]: unrecognized selector
sent to instance 0x1dd3aea0'
* First throw call stack: (0x342e03e7 0x3bfd1963 0x342e3f31 0x342e264d 0x3423a208 0x34c90d5b 0x34c9a6c3 0x34c9a56f 0x34c9a781
0x34c9acf1 0x34c99d6b 0x34c9ac31 0x34c92393 0x34c94f01 0x34c95ed7
0x34c9ecab 0x36527519 0x36527689 0x365277ab 0x3652791f 0x36527acf
0x34c95997 0x36527a41 0x3652aad1 0x3652d0d9 0x3652cfe3 0x34226acd
0x3652cf97 0x34226acd 0x3652cf97 0x34226acd 0x3652cf97 0x34226acd
0x3652cf97 0x34226acd 0x3652cf97 0x34226acd 0x3652cf97 0x34226acd
0x3652cf97 0x34226acd 0x3652cf97 0x34c95997 0x36526f3d 0x361623dd
0x35e9e513 0x35e9e0b5 0x35e9efd9 0x35e9e9c3 0x35e9e7d5 0x35e9e639
0x342b5941 0x342b3c39 0x342b3f93 0x3422723d 0x342270c9 0x37e0533b
0x361432b9 0xd3871 0xc29d8) libc++abi.dylib: terminate called throwing
an exception
the corresponding stacktrace looks like this:
or something like this:
driver(5930,0x3df85b78) malloc: * error for object 0x1e565990:
pointer being freed was not allocated
* set a breakpoint in malloc_error_break to debug (lldb)
Then the stacktrace looks like
I'm completely clueless. Has anybody got an idea? I'm using ios 6.1.
Update:
Commenting the inner nested brackets does not change anything:
[UIView beginAnimations:nil context:NULL]; {
//[UIView setAnimationCurve:UIViewAnimationCurveEaseInOut];
//[UIView setAnimationDuration:.5];
self.waiting_view.alpha = 0;
self.waiting_label.alpha = 0;
self.activity_indicator.alpha = 0;
} [UIView commitAnimations];
Update 2:
After removing the curly brackets the app still crashes as decribed.
[UIView beginAnimations:nil context:NULL];
[UIView setAnimationCurve:UIViewAnimationCurveEaseInOut];
[UIView setAnimationDuration:.5];
self.waiting_view.alpha = 0;
self.waiting_label.alpha = 0;
self.activity_indicator.alpha = 0;
[UIView commitAnimations];
Update 3:
This is the complete code that contain any of the affected ui elements in the hide_waiting_activity:
MainNavigationController.h
//Waiting overlay
#property (nonatomic,strong) UIActivityIndicatorView* activity_indicator;
#property (nonatomic,strong) UIImageView* waiting_view;
#property (nonatomic,strong) UILabel* waiting_label;
MainNavigationController.m
#implementation MainNavigationController
#synthesize activity_indicator;
#synthesize waiting_view;
#synthesize waiting_label;
...
- (void)viewDidLoad
{
[super viewDidLoad];
//Create a transparent waiting indicator view that is shown to the user while the app is working in background
waiting_view = [[UIImageView alloc] initWithFrame:CGRectMake( 0, 64.f /* top navigation bar is 64.f */, 320, 480 )];
[waiting_view setImage:[UIImage imageNamed:#"Main_Menu_Background.png"]];
waiting_view.backgroundColor = [UIColor clearColor];
self.activity_indicator = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleWhiteLarge];
[self.activity_indicator setColor:[UIColor blackColor]];
[self.activity_indicator startAnimating];
self.activity_indicator.center = CGPointMake( 160.f, (240.f-64.f) );
[waiting_view addSubview:activity_indicator];
waiting_label = [[UILabel alloc] initWithFrame:CGRectMake( 110.f, (240.f-64.f)+30.f, 100.f, 16.f)];
waiting_label.font = [UIFont boldSystemFontOfSize:13.f];
waiting_label.textColor = [UIColor blackColor];
waiting_label.backgroundColor = [UIColor clearColor];
waiting_label.textAlignment = UITextAlignmentCenter;
waiting_label.text = NSLocalizedString(#"Please_Wait_Text", #"");
[waiting_view addSubview:waiting_label];
[self.view addSubview:waiting_view];
[self.view bringSubviewToFront:self.activity_indicator];
self.waiting_view.hidden = YES;
self.activity_indicator.hidden = YES;
...
}
- (void) show_waiting_activity
{
if( self.waiting_view.alpha == 1 && self.waiting_view.hidden == NO )
return;
self.waiting_view.hidden = NO;
self.activity_indicator.hidden = NO;
[UIView beginAnimations:nil context:NULL]; {
[UIView setAnimationCurve:UIViewAnimationCurveEaseInOut];
[UIView setAnimationDuration:.2];
self.waiting_view.alpha = 1;
self.waiting_label.alpha = 1;
self.activity_indicator.alpha = 1;
} [UIView commitAnimations];
}
- (void) hide_waiting_activity
{
[UIView beginAnimations:nil context:NULL];
[UIView setAnimationCurve:UIViewAnimationCurveEaseInOut];
[UIView setAnimationDuration:.5];
self.waiting_view.alpha = 0;
self.waiting_label.alpha = 0;
self.activity_indicator.alpha = 0;
[UIView commitAnimations];
}
I'm asking myself where in this code the ui elements could be destroyed in these .5 seconds?

Answer 1

The problem isn't in the code you pasted - the problem is what's happening to the views it's referencing after the animation starts (somewhere else in your code). If the animation is running for 0.5 seconds, all those views must be alive still for the next 0.5 seconds.
So, your choices for views that are not living long enough: self, self.waiting_view, self.waiting_label, self.activity_indicator.