iOS之路7-GCD-调度组

有时须要多个异步任务都执行完成以后继续作某些事情, 调度组能够帮咱们实现

调度组的简单测试

-  (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event{
    [self group2];
}
- (void)group2 {
    
    // 1.建立group
    dispatch_group_t group = dispatch_group_create();
    // 建立全局队列
    dispatch_queue_t q = dispatch_get_global_queue(0, 0);
    
    // 2.建立并发任务
    // 入组 - 会监听后续的 block(任意,例如能够是网络方法的block)
    dispatch_group_enter(group);
    dispatch_async(q, ^{
        NSLog(@"www - %@", [NSThread currentThread]);
        
        // 出组的代码 必定放在block的最后一句 通知调度组,任务完成了
        dispatch_group_leave(group);
    });
    
    dispatch_group_enter(group);
    dispatch_async(q, ^{
        NSLog(@"mmm - %@", [NSThread currentThread]);
        
        dispatch_group_leave(group);
    });
    
    // 3.监听调度组 - 等待组中的任务都执行完毕，才会执行
    dispatch_group_notify(group, dispatch_get_main_queue(), ^{
        NSLog(@"over");
    });
}