UIView Animation Block Makes No Changes - iphone

Question

The following code is sheer simple. _facebookF is a UIImageView.
if (animationOn == YES) {
[UIView animateWithDuration:0.4 animations:^{
[_faceBookF setAlpha:0];
}];
[_faceBookF setImage:[UIImage imageNamed:#"facebookFBlue.png"]];
[UIView animateWithDuration:0.4 animations:^{
[_faceBookF setAlpha:1];
}];
} else {
[UIView animateWithDuration:0.4 animations:^{
[_faceBookF setAlpha:0];
}];
[_faceBookF setImage:[UIImage imageNamed:#"facebookF.png"]];
[UIView animateWithDuration:0.4 animations:^{
[_faceBookF setAlpha:1];
}];
}
The app gets to the method which contains this code fine, but no changes to the UI occur throughout the entire block of code. To my knowledge, the app is running on the main thread.
Any guesses?
UPDATE--In fact, the issue is that the image is not being changed at all--with or without the animation. Both images are accessed fine in other parts of the app.

Answer 1

It looks like you are trying to run sequential animations, but the way you have coded them, they are likely to run in parallel. What you need to do is this:
if (animationOn == YES) {
[UIView animateWithDuration:0.4 animations:^{
[_faceBookF setAlpha:0];
} completion:^(BOOL finished) {
[_faceBookF setImage:[UIImage imageNamed:#"facebookFBlue.png"]];
[UIView animateWithDuration:0.4 animations:^{
[_faceBookF setAlpha:1];
}];
}];
}
else {
[UIView animateWithDuration:0.4 animations:^{
[_faceBookF setAlpha:0];
}completion:^(BOOL finished) {
[_faceBookF setImage:[UIImage imageNamed:#"facebookF.png"]];
[UIView animateWithDuration:0.4 animations:^{
[_faceBookF setAlpha:1];
}];
}];
}

Answer 2

Try this. This starts the second animation after the first has completed. So it will fade out the UIImageView and then fade it up with different version of the image.
[UIView animateWithDuration: 0.4
animations:^
{
[_faceBookF setAlpha:0];
}
completion:^(BOOL finished)
{
[_faceBookF setImage:[UIImage imageNamed:#"facebookFBlue.png"]];
[UIView animateWithDuration:0.4
animations:^
{
[_faceBookF setAlpha:1];
}];
}];

Answer 3

Thanks for your responses. I've implemented the completion block you both mentioned to avoid both animations firing at once. However, the main issue had to do with the method not being accessed properly. I can't see exactly why, as the facebookF variable was not nil, and the if and log statements in the method worked fine. Anyway, I have switched to a NSNotification solution, and now all parts of the method are being accessed.