Question

[UIView animateWithDuration:1.0 animations:^(void) {
    im.transform = CGAffineTransformIdentity;
} completion:^(BOOL finished) {
    [UIView animateWithDuration:1.0 delay:1.0 options:UIViewAnimationCurveEaseOut animations:^(void) {
        im.alpha = 0.0;
    } completion:^(BOOL finished) {
        [im removeFromSuperview];
    }];    
}];

The code is for animating UIImageView, that I know;
I want to know the calling mechanism, as I haven’t seen this kind of function call for the very first time.

Mainly, What is ^(void) and why im.transform = CGAffineTransformIdentity; passed to it?

I have gone thorugh Apple docs, to find anything related to this function call, and I got it too, but I didn’t get any idea from there; or I might have been to wrong section.

Can anyone here guide me to this?

Answer 1

This is called a block, and was introduced in iOS 4 and Mac OS X 10.6.

Here are some links where you can learn more about them:

• Apple’s Documentation – Blocks Programming Topics
• Ask Big Nerd Ranch: Blocks in Objective-C
• Programming with C Blocks
• Introduction to Blocks in Objective-C – Part 1

The above example should read as follows:

// Start an animation over the next 1 second 
[UIView animateWithDuration:1.0 animations:^(void) {

    // For this animation, animate from the current value of im.transform back to the identity transform
    im.transform = CGAffineTransformIdentity;

} completion:^(BOOL finished) {  // At the completion of the first animation...

    // Wait 1 second, then start another 1-second long animation
    [UIView animateWithDuration:1.0 delay:1.0 options:UIViewAnimationCurveEaseOut animations:^(void) {

        im.alpha = 0.0;  // Fade out im during this animation

    } completion:^(BOOL finished) {  // When you complete this second animation
        [im removeFromSuperview];  // Remove im from its superview
    }];    
}];

So you will have one second where im animates the removal of its transform, a one second delay, and then a one second fadeout of im.