如何在c中异步调用任何方法＃

Question

有人能告诉我一小段代码演示了如何在c＃中异步调用一个方法吗？

Answer 1

如果使用action.BeginInvoke（），则表示have to call EndInvoke某处 - 否则框架必须在堆上保存异步调用的结果，导致内存泄漏。

如果您不想使用async/await关键字跳转到C＃5，那么您可以在.Net 4中使用Task Parallels库。它比使用BeginInvoke/EndInvoke好得多，并且提供了一个清理方式发射后不管的异步工作：

using System.Threading.Tasks; 
... 
void Foo(){} 
... 
new Task(Foo).Start(); 

如果你有方法来调用有参数的，你可以使用lambda简化呼叫，而无需创建代表：

void Foo2(int x, string y) 
{ 
    return; 
} 
... 
new Task(() => { Foo2(42, "life, the universe, and everything");}).Start(); 

我很确定（但肯定不是肯定的），C＃5 async/await语法是合理的t任务库周围的语法糖。

Answer 2

这里有一个办法做到这一点：你需要使用其它类型的委托，以取代Action

// The method to call 
void Foo() 
{ 
} 


Action action = Foo; 
action.BeginInvoke(ar => action.EndInvoke(ar), null); 

当然，如果你可以在方法具有不同的签名

Answer 3

退房MSDN文章Asynchronous Programming with Async and Await负担得起玩新的东西。它被添加到.NET 4.5中。从链接

示例代码片段（它本身从this MSDN sample code project）：

// Three things to note in the signature: 
// - The method has an async modifier. 
// - The return type is Task or Task<T>. (See "Return Types" section.) 
// Here, it is Task<int> because the return statement returns an integer. 
// - The method name ends in "Async." 
async Task<int> AccessTheWebAsync() 
{ 
    // You need to add a reference to System.Net.Http to declare client. 
    HttpClient client = new HttpClient(); 

    // GetStringAsync returns a Task<string>. That means that when you await the 
    // task you'll get a string (urlContents). 
    Task<string> getStringTask = client.GetStringAsync("http://msdn.microsoft.com"); 

    // You can do work here that doesn't rely on the string from GetStringAsync. 
    DoIndependentWork(); 

    // The await operator suspends AccessTheWebAsync. 
    // - AccessTheWebAsync can't continue until getStringTask is complete. 
    // - Meanwhile, control returns to the caller of AccessTheWebAsync. 
    // - Control resumes here when getStringTask is complete. 
    // - The await operator then retrieves the string result from getStringTask. 
    string urlContents = await getStringTask; 

    // The return statement specifies an integer result. 
    // Any methods that are awaiting AccessTheWebAsync retrieve the length value. 
    return urlContents.Length; 
} 

报价：

如果AccessTheWebAsync没有，它可以调用GetStringAsync和等待之间做任何工作完成后，您可以通过在以下单个语句中调用和等待来简化代码。

string urlContents = await client.GetStringAsync(); 

更多细节都在link。

Answer 4

public partial class MainForm : Form 
{ 
    Image img; 
    private void button1_Click(object sender, EventArgs e) 
    { 
     LoadImageAsynchronously("http://media1.santabanta.com/full5/Indian%20%20Celebrities(F)/Jacqueline%20Fernandez/jacqueline-fernandez-18a.jpg"); 
    } 

    private void LoadImageAsynchronously(string url) 
    { 
     /* 
     This is a classic example of how make a synchronous code snippet work asynchronously. 
     A class implements a method synchronously like the WebClient's DownloadData(…) function for example 
      (1) First wrap the method call in an Anonymous delegate. 
      (2) Use BeginInvoke(…) and send the wrapped anonymous delegate object as the last parameter along with a callback function name as the first parameter. 
      (3) In the callback method retrieve the ar's AsyncState as a Type (typecast) of the anonymous delegate. Along with this object comes EndInvoke(…) as free Gift 
      (4) Use EndInvoke(…) to retrieve the synchronous call’s return value in our case it will be the WebClient's DownloadData(…)’s return value. 
     */ 
     try 
     { 
      Func<Image> load_image_Async = delegate() 
      { 
       WebClient wc = new WebClient(); 
       Bitmap bmpLocal = new Bitmap(new MemoryStream(wc.DownloadData(url))); 
       wc.Dispose(); 
       return bmpLocal; 
      }; 

      Action<IAsyncResult> load_Image_call_back = delegate(IAsyncResult ar) 
      { 
       Func<Image> ss = (Func<Image>)ar.AsyncState; 
       Bitmap myBmp = (Bitmap)ss.EndInvoke(ar); 

       if (img != null) img.Dispose(); 
       if (myBmp != null) 
        img = myBmp; 
       Invalidate(); 
       //timer.Enabled = true; 
      }; 
      //load_image_Async.BeginInvoke(callback_load_Image, load_image_Async);    
      load_image_Async.BeginInvoke(new AsyncCallback(load_Image_call_back), load_image_Async);    
     } 
     catch (Exception ex) 
     { 

     } 
    } 
    protected override void OnPaint(PaintEventArgs e) 
    { 
     if (img != null) 
     { 
      Graphics grfx = e.Graphics; 
      grfx.DrawImage(img,new Point(0,0)); 
     } 
    } 

Answer 5

与.NET 4.5开始，你可以使用Task.Run简单地开始一个动作：

void Foo(string args){} 
... 
Task.Run(() => Foo("bar")); 

http://blogs.msdn.com/b/pfxteam/archive/2011/10/24/10229468.aspx