Objective-C Blocks in UIView Animations

Blocks are simply a way of creating callback code at the time of invocation. The structure is actually very similar to how typically I would create functions in Javascript. Take the following block example in Objective-C:

int (^Multiply)(int, int) = ^(int num1, int num2) {
    return num1 * num2;
int result = Multiply(7, 4); // result is 28

Look familiar? That’s because the structure is similar to Javascript:

var Multiply = function (num1, num2) {
    return num1 * num2;
var result = Multiply(7, 4); // result is 28

As a use case, I needed to execute code upon completion of an animation. Originally, I had the following code:

[self hideReportButtons]
[UIView beginAnimations:@"animationId" context:nil];
[UIView setAnimationDuration:1.0];
[UIView setAnimationTransition:UIViewAnimationTransitionCurlUp forView:webReportView cache:YES];
webReportView.hidden = YES;
[UIView commitAnimations];

Unfortunately with the above code, I didn’t have control of the timing of the execution of code. With blocks, I’m able to execute code specifically when the animation ends, which is exactly what I needed:

[UIView transitionWithView: webReportView
                  duration: 1.5
                   options: UIViewAnimationOptionTransitionCurlUp
                animations: ^{
                  webReportView.hidden = YES;
                completion: ^(BOOL finished) {
                  [self hideReportButtons];

The end result is a cleaner and more easily understandable code.

See developer.apple.com