Question

I have an NSArray named imgBall that holds a temporary variable name imgView, which displays an image on the screen when the user touches a point on the screen.

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {

    UIImageView *imgView = [[UIImageView alloc] initWithFrame:CGRectMake(40, 40, 40, 40)];
    imgView.image = [UIImage imageNamed:@"ball.png"];
    [self.view addSubview:imgView];
    imgView.center = [myTouch locationInView:self.view];
    [imgBall addObject:imgView];
}

The user can create multiple instances by touching anywhere on the screen. Could mean 5, 10, or 20 different balls in the array.

Now, i have a button that needs to ‘clear’ the screen and remove all instances of imgView.
I have tried the following:

 for (UIImageView *imgView in imgBall) {
    [self.view removeFromSuperview:imgView]; 
}

and

    for (UIImageView *imgView in imgBall) {
    [imgBall removeObject:imgView];
}

But they both yield SIGABRT and throw the exception:

Terminating app due to uncaught exception 'NSGenericException', reason: 
'*** Collection     <__NSArrayM: 0x735f4a0> was mutated while being enumerated.'

What way can i do this without getting SIGABRT thrown every time?

Answer 1

I think you want:

for (UIImageView *imgView in imgBall) {
    [imgView removeFromSuperview]; 
    [imgBall removeObject:imgView];
}

You also need to do [imgView release] after [imgBall addObject:imgView] when you create it in touchesEnded, otherwise you will leak memory.