停止在不同线程上执行的所有动画

Question

I have a menu with items popping right after each other in intervals of 3 seconds, I'm doing it like so:

for(UIButton *menuItem in menuItems){
    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (0.3 * i) * NSEC_PER_SEC), dispatch_get_current_queue(), ^{
        [menuItem setAlpha:1.0];
    }                             
}

Is it possible to stop the animation in the middle (when a button is touched, for example) ? I tried just setting everything to alpha 1.0 but as expected, the threads kept running and shows the items again.

Would appreciate any ideas:)
Shai.

Answer 1

You could do the animations using UIView block-based animations, with the delay: set. No thread worries there.

These animations can be interrupted by starting another block-based animation with the option UIViewAnimationOptionBeginFromCurrentState set.

For alpha transitions this is fine since it doesn't matter what the current position of the animation is. If you are moving objects, you can get the current position by querying the view.layer.presentationLayer which holds the current state of the object. You will need to import the QuartzCore framework to do this. This also gives you a method, removeAllAnimations which will do pretty much what it sounds like and takes any view right to the endpoint of any animations it has got pending or active.

Answer 2

I don't think you can stop animations already scheduled. But you could set an instance variable with a BOOL flag indicating if a button was already pressed or not.

For example, supposing your button's targets is the method buttonTapped .

Initialize you flag to NO .

- (id)init {
    if (self = [super init]) {
        buttonAlreadyTapped = NO;
    }

    return self;
}

In your button's targets set the flag to YES .

- (void)buttonTapped {
    self.buttonAlreadyTapped = YES;
}

And only modify the alpha if the flag is NO .

for (NSInteger i = 1; i <= [menuItems count]; i++) {        
    UIButton *menuItem = [menuItems objectAtIndex:i-1];

    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (3 * i) * NSEC_PER_SEC), dispatch_get_current_queue(), ^{
        if (!self.buttonAlreadyTapped) {
            menuItem.alpha = 1.0f;
        }
    });
}

---

Remember that sending messages to UIKit , should always be done on the main thread.

for (NSInteger i = 1; i <= [menuItems count]; i++) {        
    UIButton *menuItem = [menuItems objectAtIndex:i-1];

    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (3 * i) * NSEC_PER_SEC), dispatch_get_current_queue(), ^{
        if (!self.buttonAlreadyTapped) {
            dispatch_async(dispatch_get_main_queue(), ^{
                menuItem.alpha = 1.0f;
            });
        }
    });
}

Answer 3

也许你会在这个回复中找到答案，也许你会以其他方式做你的事情。