How Do I Declare A Block in Objective-C?

As a Local Variable

returnType (^blockName)(parameters) = ^returnType(parameters) { ... };

As a Property

@property (copy, nonatomic) returnType (^blockName)(parameters);

As a Method's parameters

- (void)someMethodWithBlocks:(returnType (^)(parameters))blockName;

As a Method's Arguments

[self someMethodWithBlock:^returnType (parameters) { ... }];

As a typedef

typedef returnType (^TypeName)(parametersTypes);
TypeName blockName = ^returnType(parameters) { ... };