Question

I have an application with multiple views that transitions to the main screen depending on which button was pressed. My current problem is that if the view is in the middle of animating then when the user selects another button then the whole layout becomes messed up. (ex: the views don’t align with the screen meaning that they become a few pixels off)

What I would like to know is if there is a way to check if the view is currently animating and if so just have it animate to the last frame and skip anything in between. Below is a small piece of code that I have just tested based on what I have read on other user asked questions on SO:

-(IBAction)buttonPress:(id)sender
{
    if([selectedView.layer.animationKeys count] > 0)
    {
        [selectedView.layer removeAllAnimations];
    }

// Perform other calculations once the animation has stopped
}

Answer 1

There are many ways to do this but….

If you are using block animations you could set a “isAnimating” flag when the animation starts and set it again in the completion block. You could check the bool from anywhere and handle cases as needed.

As for needing code to execute after an animation occurs, but

// animation code in some method...
[UIView animateWithDuration:1.0
    delay: 0.0
    options: UIViewAnimationOptionCurveEaseIn
    animations:^{
         isAnimating = YES;
         fooView.alpha = 0.0;
    }
    completion:^(BOOL finished){
         isAnimating = NO;
         [[NSNotificationCenter defaultCenter] postNotificationName:@"FooBeDone" object:nil userInfo:nil]
    }];

-(IBAction)buttonPress:(id)sender {
    if (isAnimating) {
         [[NSNotificationCenter defaultCenter] addObserver:self 
                           selector:@selector(doBar:) 
                               name:@"FooBeDone"
                             object:nil];
         // possibly disable button to prevent multiple taps?
    } else {
         [self doBar];
    }
}

- (void)doBar {
     // do what needs to be done when when the animation is over
     [[NSNotificationCenter defaultCenter] removeObserver:self name:@"FooBeDone" object:nil];
     // possibly enable button again
}

edit: I added more code to show a possible notification method. Creating extended loops in your IBAction will lock the user interface until the loop finishes and you can get back to the main run loop, so it’s highly advised to avoid it. Notifications should give you the same effect but allow your main run loop to continue unhindered.