Making a smoothly animated entrance, exit, and swapping of two image views - iphone

Question

I am using UIView's animation features to swim one image of a fish onto the screen and when there already exists a fish in the middle of the screen, swim it off and swim a new one on. The selection of the fish is sent from a separate tableview controller.
To accomplish this, I m keeping two instance variables of UIImageView and exchanging self.fishViewCurrent for self.fishViewNext once the animation is completed (see code below).
My problem is when the user presses on new table cells quickly, before the next fish has had a chance to arrive. My quick solution is to delay a new message that will add the fish and just do nothing at the moment. This works for 2 quick touches, but not more. I am looking for ideas if anyone knows how I can improve the code below, so that the animation is smooth and you can click on whatever while the final displayed image is the one last clicked. Here re the important methods:
Creating the first image view:
- (void) createFish {
self.fishViewCurrent = [[[UIImageView alloc] init] autorelease];
self.fishViewCurrent.contentMode = UIViewContentModeScaleAspectFit;
self.fishViewCurrent.bounds = CGRectMake(0.0f, 0.0f, kFishWidth, kFishHeight);
self.fishViewCurrent.center = CGPointMake(-kFishWidth, kFishYPos); // off the screen to the left
[self addSubview:self.fishViewCurrent];
}
Public method called when a tableview cell is selected:
- (void) addFish:(UIImage *)fish {
if (self.fishViewNext) {
[self performSelector:#selector(addFish:) withObject:(UIImage *)fish afterDelay:1.0];
return;
}
self.fishViewNext = [[[UIImageView alloc] initWithImage:fish] autorelease];
self.fishViewNext.contentMode = UIViewContentModeScaleAspectFit;
self.fishViewNext.bounds = CGRectMake(0.0f, 0.0f, kFishWidth, kFishHeight);
self.fishViewNext.center = CGPointMake(self.bounds.size.width + kFishWidth, kFishYPos); // off the screen right
[self addSubview:self.fishViewNext];
[UIView beginAnimations:#"swimFish" context:nil];
[UIView setAnimationDuration:2.0f];
[UIView setAnimationCurve:UIViewAnimationCurveEaseInOut];
[UIView setAnimationBeginsFromCurrentState:YES];
[UIView setAnimationDelegate:self];
[UIView setAnimationDidStopSelector:#selector(fishSwamOffHandler:finished:context:)];
[UIView setAnimationRepeatAutoreverses:NO];
self.fishViewNext.center = CGPointMake(self.center.x, kFishYPos); // center
self.fishViewCurrent.center = CGPointMake(-kFishWidth, kFishYPos); // exit stage left
[UIView commitAnimations];
}
Handler to switch the 'next' fish (UIImageView) to the 'current':
- (void)fishSwamOffHandler:(NSString *)animationID finished:(NSNumber *)finished context:(void *)context {
[self.fishViewCurrent removeFromSuperview];
self.fishViewCurrent = self.fishViewNext;
self.fishViewNext = nil;
}

Answer 1

Simplest thing would be to create an ivar BOOL, say _fishIsSwimming, and a _queuedFishView then change the beginning of addFish: to look like this:
- (void) addFish:(UIImage *)fish
{
// queue the most recent fish, if one was passed in
if(fish)
self.queuedFishView = [[[UIImageView alloc] initWithImage:fish] autorelease];
// If something is swimming, leave now
if(_fishIsSwimming)
return;
// If we get here and there's no queued fish, leave now
if(!self.queuedFishView)
return;
// We have a queued fish and nothing is swimming, so do the queued fish next
// and clear the queued fish
_fishIsSwimming = YES;
self.nextFishView = self.queuedFishView;
self.queuedFishView = nil;
// Then carry on as normal
}
Then in your animation completion callback, you do this:
-(void) fishSwamOffHandler:(NSString*)animationID finished:(NSNumber*)finished context:(void*)context
{
// We're done animating, so ready to do another swimming fish
_fishIsSwimming = NO;
[self.fishViewCurrent removeFromSuperview];
self.fishViewCurrent = self.fishViewNext;
self.fishViewNext = nil;
// now call to add another fish with nil, so that it will use
// the queued fish if there is one and otherwise just early out
[self addFish:nil];
}
So what will happen is that you'll always maintain the most recently passed in fish in the queuedFishView, and then as soon as the animation is over you can drop back into addFish, and if there's a fish waiting to go then you send it. If not you just wait for the next one sent by a button press