iOS find if a view is animating - objective-c

Question

I'm trying to animate (fade in/out) a UILabel and I'm using the following code:
float newAlpha = 0.0;
//TODO:Check if the previous animation has finished
if(answer.alpha==0.0) {
newAlpha = 1.0;
} else if(answer.alpha==1.0) {
newAlpha = 0.0;
}
[UIView animateWithDuration:1.0 animations:^{
answer.alpha = newAlpha;
}];
Where the TODO comment is, I want to check if the previous animation has finished and if it hasn't, exit the method. Is there some way of doing this?

Answer 1

UPDATE #1:
you need a variable in your class:
BOOL _animationFinished;
and then you can use the following way for the animation:
float newAlpha = 0.0;
//TODO:Check if the previous animation has finished
if (_animationFinished == false) return;
if(answer.alpha==0.0) {
newAlpha = 1.0;
} else if(answer.alpha==1.0) {
newAlpha = 0.0;
}
[UIView animateWithDuration:1.0f animations:^{ answer.alpha = newAlpha; _animationFinished = false; } completion:^(BOOL finished){ _animationFinished = true; }];
it must be work.
ORIGINAL
I'm always checking the subject of the animation in this case, like this:
float newAlpha = 0.0;
//TODO:Check if the previous animation has finished
if (answer.alpha > 0.f || answer.alpha < 1.f) return; // it is always good enough for me
// ...or with AND it will cause the same effect:
// if (answer.alpha > 0.f && answer.alpha < 1.f) return;
if(answer.alpha==0.0) {
newAlpha = 1.0;
} else if(answer.alpha==1.0) {
newAlpha = 0.0;
}
[UIView animateWithDuration:1.0 animations:^{
answer.alpha = newAlpha;
}];

Answer 2

If you're using UIView then
[UIView setAnimationDidStopSelector:#selector(animationfinished)];
-(void) animationfinished
{
animationFinished = YES;
}

Answer 3

Use animateWithDuration:animations:completion: method to do your "previous animation", and set a flag in the completion handler to indicate if it's finished or not. Then, check the same flag exactly where you have the TODO comment.
Edit: Example below
-(void) animation1 {
// assume that alpha was 0 and we want the view to appear
[UIView animateWithDuration:1.0 animations:^{
answer.alpha = 1.0;
} completion:^(BOOL finished){
fristAnimationFinished = finished;
}];
}
-(void) animation2 {
float newAlpha = 0.0;
if (!firstAnimationFinished)
return;
if(answer.alpha==0.0) {
newAlpha = 1.0;
} else if(answer.alpha==1.0) {
newAlpha = 0.0;
}
[UIView animateWithDuration:1.0 animations:^{
answer.alpha = newAlpha;
}];
}