iOS 代码块

Objective-c block syntax

How Do I Declare A Block in Objective-C?

As a local variable:

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

As a property:

@property (nonatomic, copy, nullability) returnType (^blockName)(parameterTypes);

As a method parameter:

- (void)someMethodThatTakesABlock:(returnType (^nullability)(parameterTypes))blockName;

As an argument to a method call:

[someObject someMethodThatTakesABlock:^returnType (parameters) {...}];

As a parameter to a C function:

void SomeFunctionThatTakesABlock(returnType (^blockName)(parameterTypes));

As a typedef:

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

GCD

dispatch_group_t group = dispatch_group_create();
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
NSLog(@"group one start");
dispatch_group_enter(group);
dispatch_async(queue, ^{
      // do something 
    NSLog(@"group one finish");
    dispatch_group_leave(group);
});

dispatch_group_notify(group, queue, ^{
    NSLog(@"group finished");
});```