Question

如何等到嵌套的block执行完后再执行其他代码

Answer 1

这样就能等到 3个请求都返回数据以后再刷新 ，上面这种方法 属于 手动管理gourp 还有一种是 交给系统来管理：
例如：
dispatch_queue_t queue = dispatch_get_global_queue(0, 0);
dispatch_group_t group1 = dispatch_group_create();
dispatch_group_async(group1, queue, ^{
NSLog(@"A买水果");
});
dispatch_group_async(group1, queue, ^{
NSLog(@"B买烤鸭");

});
dispatch_group_async(group1, queue, ^{
NSLog(@"C买扑克");

});
dispatch_group_async(group1, queue, ^{
NSLog(@"D买水");

});
dispatch_group_notify(group1, queue, ^{
NSLog(@"Let's go!");
});