在继续执行之前如何确保异步操作完成 [英] How to ensure completion of a async operation before continuing with execution

问题描述

我正在构建一个iOS应用，其部分代码依赖于特定任务返回的成功/失败值，该任务涉及库中的回调.我希望仅在回调返回成功/失败之后才返回此任务的返回值.但是，由于我编写了顺序代码，因此即使在回调返回成功/失败之前，也会返回返回值.

I am building an iOS app and some part of its code relies on the success/failure value returned from a particular task.This tasks involves callbacks from a library. I want the return value from this task to be returned only after the callback has returned either success/failure. But since I wrote a sequential code the return value is returned even before the callback returns a success/failure.

我研究了使用模态视图控制器，据我了解，我可以使任务从该视图控制器执行，然后将代码返回.

I looked into using modal view controllers and from what I understand I can make the task execute from this view controller and then return the code back.

但是这也不符合我的要求，因为当执行启动回调序列的代码时，我不希望显示新的视图控制器.尽管有一定的回调要求我提示用户输入信息.我在弹出窗口中执行此操作，并且考虑在弹出窗口模式内制作视图控制器.但是然后，回调仍将是主线程的一部分，并且当我的弹出窗口以模态形式呈现时，我将不会收到回调.(p).

But this also doesn't suit my requirements as when the code which initiates the callback sequence is executed I don't want a new view controller to be displayed. Although there is a certain callback which requires me to prompt the user for information. I do this in a popover and I considered making the view controller within the popover modal. But then the callbacks will still be part of the main thread and I won't receive them when my popover is presented modally(?).

根据我目前对这些概念的理解，我不知道如何进行.在iOS中有什么方法可以做到这一点?

With my current understanding of these concepts I don't know how to proceed. Is there some way to do this in iOS?

该代码做了这样的事情

The code does something like this

//In CustomTableViewController

-(void) someFunc
{
   ENUM_NAME code = [TaskController startTheTask:args];
   if(code == SUCCEEDED)
   {
      //Do Something
   }
   if(code == FAILED)
   {
      //Do Something Else
   }
}

//In TaskController

-(ENUM_NAME) startTheTask:args
{
   startWorkflow(args); //This function registers callback function with the library. 
   return finalCode; //This is returned even before it is set to SUCCEEDED/FAILED
}

-(void) onCallback:params
{
    MSG_TYPE msg = [params getMsg];

    if(msg == TASK_FAILED)
       finalCode = FAILED;
    if(msg == TASK_SUCCEEDED)
       finalCode = SUCCEEDED;
    if(msg == TASK_SHOW_PROMPT)
    {  
       [PopOverController showPopOver];
    }
}

-(void) onUserInfoAdded
{
    //This is called when Confirm is clicked in the popover
    continueWorkflow(params); //asks for the next callback to happen
}

-(void) onCancleClicked
{
    //This is called when Popover is dismissed without entering Info
    cancleWorkflow(params); //asks for result of the workflow through callback
}

推荐答案

您可以使用GCD.例如:

You can use GCD. For example:

    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
    dispatch_group_t group = dispatch_group_create();

    dispatch_group_enter(group);
    dispatch_group_async(group, queue, ^{           
         //put one process here
         dispatch_group_leave(group);  //when done
    });

    dispatch_group_enter(group);
    dispatch_group_async(group, queue, ^{           
         //put another process here
         dispatch_group_leave(group); //when done
    });

    // All updates finished
    dispatch_group_notify(group, dispatch_get_main_queue(), ^{
         // add last steps here after all processess are finished
    });

    dispatch_release(group);

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