iOS_等待多個異步操作回調完成後，執行響應代碼

 

我所做項目的需求是，當前頁面有多個網絡請求，等待所有網絡請求結束後，拿到數據，刷新View

示例代碼用 dispatch_after 當做是網絡請求了

實現如下：

dispatch_group_t group = dispatch_group_create();

dispatch_group_enter(group);
NSLog(@"執行1");
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(3 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
  dispatch_group_leave(group);
  NSLog(@"完成1");
});

dispatch_group_enter(group);
NSLog(@"執行2");
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(4 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
  dispatch_group_leave(group);
  NSLog(@"完成2");
});

dispatch_group_enter(group);
NSLog(@"執行3");
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(2 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
  dispatch_group_leave(group);
  NSLog(@"完成3");
});

dispatch_group_notify(group, dispatch_get_main_queue(), ^{
  NSLog(@"都完成後，執行");
});