iOS Components and Frameworks: Understanding the Advanced Features of the iOS SDK

Using Blocks as Method Parameters

Another method of using blocks is to use them as method parameters. A common use case for this is a completion handler for a long-running or asynchronous task. To use a block as a completion handler, first a method must be declared with a completion block as a parameter.

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- (void)longRunningTaskWithCompletionHandler:   (void(^)(void))completionBlock{    ...    if (completionBlock) {        completionBlock();    }}

The syntax might look a bit awkward, but the method declares that it should receive a block with no parameters and no return type as a parameter. When the method has completed, it will execute the passed-in completion block. This allows the caller to avoid having to set ...