setAnimationDuration... its just not happening...

gabacus · 06-20-2009, 10:02 PM

hello all

i am trying fade a view in and out... which is simple in concept... but for some reason my code fires instantaneously rather than taken the specified amount of time to animate the transition. here is my code

Code:

- (void) fadeIn {
	[[self myView] setAlpha:0.0];
	[UIView beginAnimations:nil context:NULL];
	[UIView setAnimationDuration:2.0f];
	[UIView setAnimationCurve:UIViewAnimationCurveEaseIn];
	[UIView setAnimationBeginsFromCurrentState:YES];
	[UIView setAnimationDelegate:self];
	[UIView setAnimationDidStopSelector:@selector(fadeOut)];
	
	[[self myView] setAlpha:0.8];
	
	[UIView commitAnimations];
}

- (void) fadeOut {
	NSLog(@"fadeOut called"); // just a marker so i can see if this is being called after 2 seconds
}

my problem is when fadeIn is called, the alpha is immediately set to 0.8 and fadeOut is called (i can see the nslog statement pop up as soon as i see the view)

any idea's as to why this is happening?

**ftm** · 06-21-2009, 12:46 PM

When setting the alpha, try using:

Code:

myView.alpha = 0.0;

and

Code:

myView.alpha = 0.8;

And you should not need this line at all:

Code:

[UIView setAnimationBeginsFromCurrentState:YES];

**smasher** · 06-21-2009, 03:51 PM

Where are you calling "fadeIn" from? If it's in the view's init or viewDidLoad, it's probably too soon. Try it from viewWillAppear instead.

Also, your stop selector should have this signature; this shouldn't keep fadeIn from working, though.

Code:

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

gabacus · 06-22-2009, 08:28 AM

thanks for the responses guys!

i finally got it working

i ended up calling the animation blocks from the viewDidLoad method and it is now working the way i want it too. im not sure why it was causing problems though... where can i read up more on this?

smasher, i have not seen the animationDidStop method before and im not really sure how to use it...

[UIView setAnimationDidStopSelector:@selector(fadeOut)];

seems to be working fine for me. is it likely to cause problems? what is the difference between the 2 methods?

bshirley · 09-01-2009, 01:59 AM

The trick is you need to setAnimationDuration: (and all the other animation values) before you setAlpha:.
The behind-the-scenes animation setup gets created when you set the value being animated.

Also, what smasher was saying about the setAnimationDidStopSelector: is that UIView assumes a method signature identical to

Code:

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

which is to say you could call it:

Code:

- (void)x:(NSString *)id y:(NSNumber *)boolNumber z:(void *)nothing;

and still be in good programming style,

you obviously aren't using any of the parameters, so your callback will work,
the additional parameters are pushed onto the stack and ignored,

not guaranteed safe in all architectures of Objective-C, but okay on Intel and iPhone processors,

I would suggest something like:

Code:

[UIView setAnimationDidStopSelector:@selector(fadeInDidStop:finished:context:)];

- (void)fadeInDidStop:(NSString *)animationID finished:(NSNumber *)finished context:(void *)context;

**mr tickle** · 11-19-2009, 09:10 AM

i would also like to say something i have discovered

the uiview animation expects something that is tangible inside of the animation block

i noticed that on some operations that are not interpolative, it doesnt work, ie, i can specify 6.0 seconds for the delay, and inside of the block, do something that does not interpolate from 0 to a value, it doesnt wait the 6.0 seconds, it skips straight to the finished method you specified.

correct me if i am wrong