委派任务并在完成时收到通知（在 C# 中）

Question

从概念上讲，我想完成以下任务，但无法理解如何在 C# 中正确编码：

SomeMethod { // Member of AClass{}
    DoSomething;
    Start WorkerMethod() from BClass in another thread;
    DoSomethingElse;
}

然后，当 WorkerMethod() 完成时，运行以下命令：

void SomeOtherMethod()  // Also member of AClass{}
{ ... }

谁能举个例子吗？

Answer 1

这 后台工作者 为此，.NET 2.0 中添加了该类。

简而言之，你这样做：

BackgroundWorker worker = new BackgroundWorker();
worker.DoWork += delegate { myBClass.DoHardWork(); }
worker.RunWorkerCompleted += new RunWorkerCompletedEventHandler(SomeOtherMethod);
worker.RunWorkerAsync();

如果需要，您还可以添加取消和进度报告等精美的内容:)

Answer 2

在.Net 2中引入了BackgroundWorker，这使得运行异步操作变得非常容易：

BackgroundWorker bw = new BackgroundWorker { WorkerReportsProgress = true };

bw.DoWork += (sender, e) => 
   {
       //what happens here must not touch the form
       //as it's in a different thread
   };

bw.ProgressChanged += ( sender, e ) =>
   {
       //update progress bars here
   };

bw.RunWorkerCompleted += (sender, e) => 
   {
       //now you're back in the UI thread you can update the form
       //remember to dispose of bw now
   };

worker.RunWorkerAsync();

在.Net 1 中你必须使用线程。

Answer 3

您必须使用 AsyncCallBacks。您可以使用 AsyncCallBacks 指定方法的委托，然后指定目标方法执行完成后调用的 CallBack 方法。

这是一个小例子，你自己运行一下看看。

班级程序{

    public delegate void AsyncMethodCaller();


    public static void WorkerMethod()
    {
        Console.WriteLine("I am the first method that is called.");
        Thread.Sleep(5000);
        Console.WriteLine("Exiting from WorkerMethod.");
    }

    public static void SomeOtherMethod(IAsyncResult result)
    {
        Console.WriteLine("I am called after the Worker Method completes.");
    }



    static void Main(string[] args)
    {
        AsyncMethodCaller asyncCaller = new AsyncMethodCaller(WorkerMethod);
        AsyncCallback callBack = new AsyncCallback(SomeOtherMethod);
        IAsyncResult result = asyncCaller.BeginInvoke(callBack, null);
        Console.WriteLine("Worker method has been called.");
        Console.WriteLine("Waiting for all invocations to complete.");
        Console.Read();

    }
}

Answer 4

虽然这里有几种可能性，但我会使用委托，异步调用使用 BeginInvoke 方法。

警告 :不要忘记随时打电话 EndInvoke 于 IAsyncResult 以避免最终的内存泄漏，如中所述 本文.

Answer 5

查看BackgroundWorker。

Answer 6

使用异步委托：

// Method that does the real work
public int SomeMethod(int someInput)
{
Thread.Sleep(20);
Console.WriteLine(”Processed input : {0}”,someInput);
return someInput+1;
} 


// Method that will be called after work is complete
public void EndSomeOtherMethod(IAsyncResult result)
{
SomeMethodDelegate myDelegate = result.AsyncState as SomeMethodDelegate;
// obtain the result
int resultVal = myDelegate.EndInvoke(result);
Console.WriteLine(”Returned output : {0}”,resultVal);
}

// Define a delegate
delegate int SomeMethodDelegate(int someInput);
SomeMethodDelegate someMethodDelegate = SomeMethod;

// Call the method that does the real work
// Give the method name that must be called once the work is completed.
someMethodDelegate.BeginInvoke(10, // Input parameter to SomeMethod()
EndSomeOtherMethod, // Callback Method
someMethodDelegate); // AsyncState

Answer 7

好吧，我不确定你想如何解决这个问题。从您的示例来看，WorkerMethod 似乎没有创建自己的线程来执行，但您想在另一个线程上调用该方法。

在这种情况下，创建一个简短的工作方法，调用 WorkerMethod，然后调用 SomeOtherMethod，并在另一个线程上将该方法排队。然后，当 WorkerMethod 完成时，调用 SomeOtherMethod。例如：

public class AClass
{
    public void SomeMethod()
    {
        DoSomething();

        ThreadPool.QueueUserWorkItem(delegate(object state)
        {
            BClass.WorkerMethod();
            SomeOtherMethod();
        });

        DoSomethingElse();
    }

    private void SomeOtherMethod()
    {
        // handle the fact that WorkerMethod has completed. 
        // Note that this is called on the Worker Thread, not
        // the main thread.
    }
}