What is the best way to wait for a loop of UIView animations to finish?

Question

I'm trying to loop over multiple UIViews and perform animation on each, but I'd like to know when all of the animations have finished. What is the best way to call a function when the loop of animations has finished? Alternately, is there a way to wait until all have finished?

I tried using setAnimationDidStopSelector, but it doesn't fire. In this case, I'm clearing some "chips" off a game board by having them fade out then get removed (NumberedChipView is a subclass of UIView). Play cannot continue until the chips are off the board.

[UIView beginAnimations:nil context:nil]; 
[UIView setAnimationDelegate: self];
[UIView setAnimationDidStopSelector:@selector(animationDidStop)]; 

// clear chips 
for (HexagonalTile *aTile in tilesToClear) {

    NumberedChipView *chipView = [self chipViewForColumn:aTile.column andRow:aTile.row];

    [UIView animateWithDuration:0.5 delay:0.3 options:UIViewAnimationCurveLinear animations:^{
        chipView.alpha = 0.0; 
    } 
        completion:^(BOOL finished){

         if (finished) {

             [chipView removeFromSuperview]; 
             [self.chipViews removeObject:chipView];

         }
     }]; 
}

[UIView commitAnimations]; 

I also tried CATransaction to no avail:

[CATransaction begin];  

[CATransaction setCompletionBlock:^{
    [self animationFinished]; 
}];  

// clear chips 
for (HexagonalTile *aTile in tilesToClear) {

    NumberedChipView *chipView = [self chipViewForColumn:aTile.column andRow:aTile.row];

    [UIView animateWithDuration:0.5 delay:0.3 options:UIViewAnimationCurveLinear animations:^{
        chipView.alpha = 0.0; 
    } 
        completion:^(BOOL finished){

         if (finished) {

             [chipView removeFromSuperview]; 
             [self.chipViews removeObject:chipView];

             //NSLog(@"clearing finished"); 
         }
     }]; 
}

[CATransaction commit]; 

Update:

I now can get the selector to fire, however it doesn't wait for the loop of animations to finish.

[UIView setAnimationDidStopSelector:@selector(animationDidStop:finished:)];

Answer 1

Your for loop is firing off all the animations with the same delay and same duration, so they will all start and finish at the same time.

Your completion method is going to be called once for each of your animations.

You could rewrite your code slightly to set a counter to zero before entering the loop, and increment it after each step. When the index is less than the array count, pass a nil completion block. Once the index == the array count, you're on the last item, so pass in a completion block with the code that you want to invoke once the last animation completes.

Note that you can use this index approach to make each animation start at a different time, by increasing the delay amount based on the index value:

delay = .3 + (0.5 * index);

Answer 2

Here's what ended up working for me. I realized that the UIView animateWithDuration methods weren't being associated to the begin/commit section. Rather, the begin/commit sections mark a region of "implicit" animation operations, so I could just set the properties within the animation and it would be implicitly animated.

For example, within the animation below, I simply set the alpha property of the chipView to "0.0" and the chipView (a UIView) is implicitly animated to disappear.

[UIView beginAnimations:@"tilescleared" context:nil]; 
[UIView setAnimationDelegate: self];
[UIView setAnimationDelay:0.3]; 
[UIView setAnimationDuration:0.5]; 
[UIView setAnimationDidStopSelector:@selector(animationDidStop:finished:context:)]; 

for (HexagonalTile *aTile in tilesToClear) {

    NumberedChipView *chipView = [self chipViewForColumn:aTile.column andRow:aTile.row];

    chipView.alpha = 0.0; 

}

[UIView commitAnimations];

Then, in my animationDidStop method, I do the "cleanup" and remove and chips from the superview. This animationDidStop method only gets fired when all chipView animations from the loop have finished, which is the tricky thing I was trying to figure out.

- (void)animationDidStop:(NSString *)animationID finished:(NSNumber *)finished context:(void *)context 
{

    if ([animationID isEqualToString:@"tilescleared"]
                  && [finished boolValue]) {

       for (HexagonalTile *aTile in self.animationInfo.tilesToClear) {

           NumberedChipView *chipView = [self chipViewForColumn:aTile.column andRow:aTile.row];

           [chipView removeFromSuperview]; 
           [self.chipViews removeObject:chipView];
       }

   }

}