Declare A Block in Objective-C

gistfile1.txt

As a local variable:
returnType (^blockName)(parameterTypes) = ^returnType(parameters) {...};

As a property:
@property (nonatomic, copy) returnType (^blockName)(parameterTypes);

As a method parameter:
- (void)someMethodThatTakesABlock:(returnType (^)(parameterTypes))blockName;

As an argument to a method call:
[someObject someMethodThatTakesABlock: ^returnType (parameters) {...}];

As a typedef:
typedef returnType (^TypeName)(parameterTypes);
TypeName blockName = ^returnType(parameters) {...};