![]() With typedefs, you inherit the same Xcode auto complete features as you do with explicit block declarations. (void) performWithCompletion: (M圜ustomCompletionBlock) completionBlock typedef void (^M圜ustomCompletionBlock)(BOOL finished) Here's an example that defines a type and then uses it in a method signature identical to the example you just saw. You can go the standard route and specify a full block argument declaration like this: - (void) performWithCompletion: (void (^)(BOOL finished)) completionBlock Īlternatively you simplify matters by declaring a custom block type in your class header file. ![]() For example, say you're building a class whose instances performs an action and, when finished, permit you to execute an optional completion block. (It offers a more workplace friendly URL as well.) These sites reflect the fussy detail reality associated with block declaration and use.įigure 4 Xcode block-expanding autocomplete isn't just for system-supplied APIsīlock typedefs are incredibly useful. Various sites have sprung up to provide quick block syntax references including at least one with an honest but not-safe-for-work name. Most iOS developers now regularly use blocks in their projects (see Figure 1) using system-supplied and custom APIs but there's often confusion as to exact implementation details. This is crazy convenient, ensuring that any relevant state can be used exactly when it's needed. Block parameters instead reflect information that won't be available until the block is executed. That means you don't have to pass massive numbers of parameters to blocks to keep them in sync. This enables you to refer to variables defined in the parent's lexical scope from within the block itself. Unlike method selectors and function pointers, blocks carry that state with them for when they're executed. Closures are objects that encapsulate both behaviors and state. This approach improves readability and inspection because the way items react before, during, and after some process are most relevant at the point where that process is defined.įirst introduced in iOS 4, blocks create functional closures. ![]() Blocks enable you to move those implementation details away from isolated callbacks and into the actual context where they're most meaningful. You pass blocks to methods and functions as arguments so that they can be stored and executed at later times. Core iOS Developer's Cookbook, The, 5th Editionīlocks are one of the most fundamentally useful iOS technologies. ![]()
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