委派任务并在完成时收到通知（在C＃中）

Question

从概念上讲，我想完成以下操作，但却无法理解如何在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：

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

任何人都可以举一个例子吗？

Answer 1

为了这个目的， BackgroundWorker类已添加到.NET 2.0中。

简而言之，你做到：

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

如果你想要，你还可以添加像取消和进度报告这样的花哨的东西:)

Answer 2

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

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，您必须使用线程。

Answer 3

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

这是一个小例子，运行并亲自看看。

课程{

    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，但我会使用一个委托，使用BeginInvoke方法异步调用。

警告 ：不要忘记始终在IAsyncResult上调用EndInvoke以避免最终的内存泄漏，如本文所述 。

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，我不确定你想怎么做。 在您的示例中，看起来WorkerMethod不会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，创建一个调用WorkerMethod然后调用SomeOtherMethod的short worker方法，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.
    }
}