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

Capturing State with Blocks

When assigning a block literal, variables from the current lexical scope can be used in the block. An important characteristic of this use is that, by default, the value of those variables is “captured” or locked to the value at the time when the block is assigned. Even if the value of that variable is changed before the block is executed, the value at the time of assignment is what is used in the block execution. This example modifies the previous example to use an NSString* from the enclosing scope in the block, rather than a parameter.

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NSString *blockTestString = @"Block Test ";NSString *(^repeatString) (int);repeatString = ^NSString* (int numTimes){    NSMutableString *retString = ...