What is __ block Objective-C?

__block is a storage qualifier that can be used in two ways: Marks that a variable lives in a storage that is shared between the lexical scope of the original variable and any blocks declared within that scope. And clang will generate a struct to represent this variable, and use this struct by reference(not by value).

How do you declare a block in Objective-C?

How Do I Declare A Block in Objective-C?

1. As a local variable: returnType (^blockName)(parameterTypes) = ^returnType(parameters) {…};
2. As a property:
3. As a method parameter:
4. As an argument to a method call:
5. As a parameter to a C function:
6. As a typedef:

What is property in Objective-C?

Properties in Objective-C are used to store data in instances of classes. They define memory management, type, and access attributes of the values they store such as strong , weak , assign , readonly , readwrite , etc. strong , weak , assign property attributes define how memory for that property will be managed.

What do you mean by Objective C blocks?

Objective-C Blocks. An Objective-C class defines an object that combines data with related behavior. Sometimes, it makes sense just to represent a single task or unit of behavior, rather than a collection of methods.

What does caret ( ^ ) mean in Objective C?

This is quite similar to a C function declaration, with one great exception: The caret (^) symbol, which indicates that the declared object is a block. Let’s see everything one by one: ReturnType: Any data type Objective-C supports, or void if the block returns nothing. ^blockName: Always remember that the block name is preceded by the ^ symbol.

How to pass parameters to a block in Objective C?

Remember that both the ^ and the block name are enclosed in parentheses (). Parameters: The list of parameters you want to pass on the block, just like you do when declaring methods. However, keep in mind an important notice: When you pass no parameters to block, then the void keyword should be always set.

What does the ” _ _ block ” keyword mean?

__block is a storage qualifier that can be used in two ways: Marks that a variable lives in a storage that is shared between the lexical scope of the original variable and any blocks declared within that scope.