iOS: simple animation - objective-c

Question

I want to create a simple animation changing alpha value:
[UIView beginAnimations:nil context:NULL];
[UIView setAnimationDuration:2];
[view1 setAlpha:0.00];
[UIView commitAnimations];
Ok in this way I change the alpha value for two seconds and it works fine, but I want this thing:
When alpha is 0 the animation must should start another time to alpha = 1
So the animation should be: alpha 0 -> alpha 1 -> alpha 0 -> alpha 1 -> ... and so on with a duration of two seconds.
Can you help me?
my complete code is
-(IBAction){
FirstViewController *firstViewController = [[[FirstViewController alloc] init]autorelease];
[firstViewController.label1 setAlpha:1.00];
[firstViewController.label2 setAlpha:1.00];
view = firstViewController.viewFirst; //this is my view and I copy in other view
[self fadeOut:nil finished:nil context:nil];}
- (void) fadeOut:(NSString *)animationID finished:(NSNumber *)finished context:(void *)context {
[UIView beginAnimations:nil context:NULL];
[UIView setAnimationDuration:2];
[UIView setAnimationDelegate:self];
[UIView setAnimationDidStopSelector:#selector(fadeIn:finished:context:) ];
[view setAlpha:0.00];
[UIView commitAnimations];
}
- (void) fadeIn:(NSString *)animationID finished:(NSNumber *)finished context:(void *)context {
[UIView beginAnimations:nil context:NULL];
[UIView setAnimationDuration:2];
[UIView setAnimationDelegate:self];
[UIView setAnimationDidStopSelector:#selector(fadeOut:finished:context:) ];
[view setAlpha:1.00];
[UIView commitAnimations];
}

Answer 1

In iOS 4 and later you can do
view1.alpha = 1.0;
[UIView animateWithDuration:2.0
delay:0.0
options:UIViewAnimationOptionRepeat|UIViewAnimationAutoReverse
animations:^{
view1.alpha = 0.0;
}
completion:nil
];

Answer 2

- (void) fadeOut:(NSString *)animationID finished:(NSNumber *)finished context:(void *)context {
[UIView beginAnimations:nil context:NULL];
[UIView setAnimationDuration:2];
[UIView setAnimationDelegate:self];
if(animationRunning){
[UIView setAnimationDidStopSelector:#selector(fadeIn:finished:context:) ];
}
[view1 setAlpha:0.00];
[UIView commitAnimations];
}
- (void) fadeIn:(NSString *)animationID finished:(NSNumber *)finished context:(void *)context {
[UIView beginAnimations:nil context:NULL];
[UIView setAnimationDuration:2];
[UIView setAnimationDelegate:self];
if(animationRunning){
[UIView setAnimationDidStopSelector:#selector(fadeOut:finished:context:) ];
}
[view1 setAlpha:1.00];
[UIView commitAnimations];
}
These will call each other on the end of the animation...
All you need to do to start the ball rolling is call:
[self fadeOut:nil finished:nil context:nil];

Answer 3

You can set a animation completion handler (either using the block-based API or +(void)setAnimationDidStopSelector:(SEL)selector) and start the next one.
Alternatively have a look at those to methods:
+ setAnimationRepeatCount:
+ setAnimationRepeatAutoreverses:

Answer 4

I think, you can use just one function (based on previous answer's functions):
- (void) fadeIn:(NSString *)animationID finished:(NSNumber *)finished context:(void *)context {
[UIView beginAnimations:nil context:NULL];
[UIView setAnimationDuration:2];
[UIView setAnimationDelegate:self];
[UIView setAnimationDidStopSelector:#selector(fadeIn:finished:context:) ];
[view1 setAlpha:mod(1-view1.alpha)];
[UIView commitAnimations];
}
The alplha must not be a negative value, so a mod must be applied

Answer 5

You create a ViewController like below
FirstViewController *firstViewController = [[[FirstViewController alloc] init]autorelease];
And then adding animation to it, but when did you add firstViewController.view in view heirarchy(addSubview). Also just calling
[[[FirstViewController alloc] init]autorelease]
wont create label object unless you have override its init method. Try debugging if label is allocated at that point of time.
Also for animation i use uiview anitmation with completion block method