C#異步調(diào)用四大方法詳解 收藏
讓我們首先了解下什么時候用到C#異步調(diào)用：
.NET Framework 允許您C#異步調(diào)用任何方法。定義與您需要調(diào)用的方法具有相同簽名的委托；公共語言運行庫將自動為該委托定義具有適當簽名的 BeginInvoke 和 EndInvoke 方法。
BeginInvoke 方法：用于啟動C#異步調(diào)用。它與您需要異步執(zhí)行的方法具有相同的參數(shù)，只不過還有兩個額外的參數(shù)（將在稍后描述）。BeginInvoke 立即返回，不等待C#異步調(diào)用完成。BeginInvoke 返回 IasyncResult，可用于監(jiān)視調(diào)用進度。
EndInvoke 方法：用于檢索C#異步調(diào)用結(jié)果。調(diào)用 BeginInvoke 后可隨時調(diào)用 EndInvoke 方法；如果C#異步調(diào)用未完成，EndInvoke 將一直阻塞到C#異步調(diào)用完成。EndInvoke 的參數(shù)包括您需要異步執(zhí)行的方法的 out 和 ref 參數(shù)（在 Visual Basic 中為 ByRef 和 ByRef）以及由 BeginInvoke 返回的 IAsyncResult。
注意 Visual Studio .NET 中的智能感知功能會顯示 BeginInvoke 和 EndInvoke 的參數(shù)。如果您沒有使用 Visual Studio 或類似的工具，或者您使用的是 C# 和 Visual Studio .NET，請參見異步方法簽名獲取有關(guān)運行庫為這些方法定義的參數(shù)的描述。
本主題中的代碼演示了四種使用 BeginInvoke 和 EndInvoke 進行C#異步調(diào)用的常用方法。調(diào)用了 BeginInvoke 后，可以：
• 進行某些操作，然后調(diào)用 EndInvoke 一直阻塞到調(diào)用完成。
• 使用 IAsyncResult.AsyncWaitHandle 獲取 WaitHandle，使用它的 WaitOne 方法將執(zhí)行一直阻塞到發(fā)出 WaitHandle 信號，然后調(diào)用 EndInvoke。
• 輪詢由 BeginInvoke 返回的 IAsyncResult，確定C#異步調(diào)用何時完成，然后調(diào)用 EndInvoke。
• 將用于回調(diào)方法的委托傳遞給 BeginInvoke。該方法在C#異步調(diào)用完成后在 ThreadPool 線程上執(zhí)行，它可以調(diào)用 EndInvoke。
警告：始終在C#異步調(diào)用完成后調(diào)用 EndInvoke。
測試方法和異步委托
四個示例全部使用同一個長期運行的測試方法 TestMethod。該方法顯示一個表明它已開始處理的控制臺信息，休眠幾秒鐘，然后結(jié)束。TestMethod 有一個 out 參數(shù)（在 Visual Basic 中為 ByRef），它演示了如何將這些參數(shù)添加到 BeginInvoke 和 EndInvoke 的簽名中。您可以用類似的方式處理 ref 參數(shù)（在 Visual Basic 中為 ByRef）。
下面的代碼示例顯示 TestMethod 以及代表 TestMethod 的委托；若要使用任一示例，請將示例代碼追加到這段代碼中。
注意 為了簡化這些示例，TestMethod 在獨立于 Main() 的類中聲明。或者，TestMethod 可以是包含 Main() 的同一類中的 static 方法（在 Visual Basic 中為 Shared）。
1、C#異步調(diào)用四大方法之使用 EndInvoke 等待異步調(diào)用
異步執(zhí)行方法的最簡單方式是以 BeginInvoke 開始，對主線程執(zhí)行一些操作，然后調(diào)用 EndInvoke。EndInvoke 直到C#異步調(diào)用完成后才返回。這種技術(shù)非常適合文件或網(wǎng)絡(luò)操作，但是由于它阻塞 EndInvoke，所以不要從用戶界面的服務線程中使用它。
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using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;
namespace ConsoleAppAsync
{
// The delegate must have the same signature as the method
// you want to call asynchronously.
public delegate string AsyncDelegate(int callDuration, out int threadId);
public class AsyncDemo
{
// The method to be executed asynchronously.
//
public string TestMethod(int callDuration, out int threadId)
{
Console.WriteLine("Test method begins.");
Thread.Sleep(callDuration);
threadId = AppDomain.GetCurrentThreadId();
return "MyCallTime was " + callDuration.ToString();
}
}
class Program1
{
static void Main(string[] args)
{
// The asynchronous method puts the thread id here.
int threadId;
// Create an instance of the test class.
AsyncDemo ad = new AsyncDemo();
// Create the delegate.
AsyncDelegate dlgt = new AsyncDelegate(ad.TestMethod);
// Initiate the asychronous call.
IAsyncResult ar = dlgt.BeginInvoke(3000,out threadId, null, null);
Thread.Sleep(0);
Console.WriteLine("Main thread {0} does some work.",AppDomain.GetCurrentThreadId());
// Call EndInvoke to Wait for
//the asynchronous call to complete,
// and to retrieve the results.
string ret = dlgt.EndInvoke(out threadId, ar);
Console.WriteLine("The call executed on thread {0},with return value \"{1}\".", threadId, ret);
}
}
}
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;
namespace ConsoleAppAsync
{
// The delegate must have the same signature as the method
// you want to call asynchronously.
public delegate string AsyncDelegate(int callDuration, out int threadId);
public class AsyncDemo
{
// The method to be executed asynchronously.
//
public string TestMethod(int callDuration, out int threadId)
{
Console.WriteLine("Test method begins.");
Thread.Sleep(callDuration);
threadId = AppDomain.GetCurrentThreadId();
return "MyCallTime was " + callDuration.ToString();
}
}
class Program1
{
static void Main(string[] args)
{
// The asynchronous method puts the thread id here.
int threadId;
// Create an instance of the test class.
AsyncDemo ad = new AsyncDemo();
// Create the delegate.
AsyncDelegate dlgt = new AsyncDelegate(ad.TestMethod);
// Initiate the asychronous call.
IAsyncResult ar = dlgt.BeginInvoke(3000,out threadId, null, null);
Thread.Sleep(0);
Console.WriteLine("Main thread {0} does some work.",AppDomain.GetCurrentThreadId());
// Call EndInvoke to Wait for
//the asynchronous call to complete,
// and to retrieve the results.
string ret = dlgt.EndInvoke(out threadId, ar);
Console.WriteLine("The call executed on thread {0},with return value \"{1}\".", threadId, ret);
}
}
}
運行結(jié)果：
Main thread 4332 does some work.
Test method begins.
The call executed on thread 3640,with return value "MyCallTime was 5000".
請按任意鍵繼續(xù). . .
2、C#異步調(diào)用四大方法之使用 WaitHandle 等待異步調(diào)用
等待 WaitHandle 是一項常用的線程同步技術(shù)。您可以使用由 BeginInvoke 返回的 IAsyncResult 的 AsyncWaitHandle 屬性來獲取 WaitHandle。C#異步調(diào)用完成時會發(fā)出 WaitHandle 信號，而您可以通過調(diào)用它的 WaitOne 等待它。
如果您使用 WaitHandle，則在C#異步調(diào)用完成之后，但在通過調(diào)用 EndInvoke 檢索結(jié)果之前，可以執(zhí)行其他處理。
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using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;
namespace ConsoleAppAsync
{
// The delegate must have the same signature as the method
// you want to call asynchronously.
public delegate string AsyncDelegate(int callDuration, out int threadId);
public class AsyncDemo
{
// The method to be executed asynchronously.
//
public string TestMethod(int callDuration, out int threadId)
{
Console.WriteLine("Test method begins.");
Thread.Sleep(callDuration);
threadId = AppDomain.GetCurrentThreadId();
return "MyCallTime was " + callDuration.ToString();
}
}
class Program2
{
static void Main(string[] args)
{
// The asynchronous method puts the thread id here.
int threadId;
// Create an instance of the test class.
AsyncDemo ad = new AsyncDemo();
// Create the delegate.
AsyncDelegate dlgt = new AsyncDelegate(ad.TestMethod);
// Initiate the asychronous call.
IAsyncResult ar = dlgt.BeginInvoke(3000,out threadId, null, null);
Thread.Sleep(0);
Console.WriteLine("Main thread {0} does some work.",AppDomain.GetCurrentThreadId());
// Wait for the WaitHandle to become signaled.
ar.AsyncWaitHandle.WaitOne();
// Perform additional processing here.
// Call EndInvoke to retrieve the results.
string ret = dlgt.EndInvoke(out threadId, ar);
Console.WriteLine("The call executed on thread {0}, with return value \"{1}\".", threadId, ret);
}
}
}
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;
namespace ConsoleAppAsync
{
// The delegate must have the same signature as the method
// you want to call asynchronously.
public delegate string AsyncDelegate(int callDuration, out int threadId);
public class AsyncDemo
{
// The method to be executed asynchronously.
//
public string TestMethod(int callDuration, out int threadId)
{
Console.WriteLine("Test method begins.");
Thread.Sleep(callDuration);
threadId = AppDomain.GetCurrentThreadId();
return "MyCallTime was " + callDuration.ToString();
}
}
class Program2
{
static void Main(string[] args)
{
// The asynchronous method puts the thread id here.
int threadId;
// Create an instance of the test class.
AsyncDemo ad = new AsyncDemo();
// Create the delegate.
AsyncDelegate dlgt = new AsyncDelegate(ad.TestMethod);
// Initiate the asychronous call.
IAsyncResult ar = dlgt.BeginInvoke(3000,out threadId, null, null);
Thread.Sleep(0);
Console.WriteLine("Main thread {0} does some work.",AppDomain.GetCurrentThreadId());
// Wait for the WaitHandle to become signaled.
ar.AsyncWaitHandle.WaitOne();
// Perform additional processing here.
// Call EndInvoke to retrieve the results.
string ret = dlgt.EndInvoke(out threadId, ar);
Console.WriteLine("The call executed on thread {0}, with return value \"{1}\".", threadId, ret);
}
}
}
運行結(jié)果：
Main thread 6864 does some work.
Test method begins.
The call executed on thread 7044, with return value "MyCallTime was 3000".
請按任意鍵繼續(xù). . .
3、C#異步調(diào)用四大方法之輪詢異步調(diào)用完成
您可以使用由 BeginInvoke 返回的 IAsyncResult 的 IsCompleted 屬性來發(fā)現(xiàn)C#異步調(diào)用何時完成。從用戶界面的服務線程中進行C#異步調(diào)用時可以執(zhí)行此操作。輪詢完成允許用戶界面線程繼續(xù)處理用戶輸入。
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using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;
namespace ConsoleAppAsync
{
// The delegate must have the same signature as the method
// you want to call asynchronously.
public delegate string AsyncDelegate(int callDuration, out int threadId);
public class AsyncDemo
{
// The method to be executed asynchronously.
//
public string TestMethod(int callDuration, out int threadId)
{
Console.WriteLine("Test method begins.");
Thread.Sleep(callDuration);
threadId = AppDomain.GetCurrentThreadId();
return "MyCallTime was " + callDuration.ToString();
}
}
class Program3
{
static void Main(string[] args)
{
// The asynchronous method puts the thread id here.
int threadId;
// Create an instance of the test class.
AsyncDemo ad = new AsyncDemo();
// Create the delegate.
AsyncDelegate dlgt = new AsyncDelegate(ad.TestMethod);
// Initiate the asychronous call.
IAsyncResult ar = dlgt.BeginInvoke(3000,out threadId, null, null);
// Poll while simulating work.
while (ar.IsCompleted == false)
{
Thread.Sleep(10);
}
// Call EndInvoke to retrieve the results.
string ret = dlgt.EndInvoke(out threadId, ar);
Console.WriteLine("The call executed on thread {0}, with return value \"{1}\".", threadId, ret);
}
}
}
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;
namespace ConsoleAppAsync
{
// The delegate must have the same signature as the method
// you want to call asynchronously.
public delegate string AsyncDelegate(int callDuration, out int threadId);
public class AsyncDemo
{
// The method to be executed asynchronously.
//
public string TestMethod(int callDuration, out int threadId)
{
Console.WriteLine("Test method begins.");
Thread.Sleep(callDuration);
threadId = AppDomain.GetCurrentThreadId();
return "MyCallTime was " + callDuration.ToString();
}
}
class Program3
{
static void Main(string[] args)
{
// The asynchronous method puts the thread id here.
int threadId;
// Create an instance of the test class.
AsyncDemo ad = new AsyncDemo();
// Create the delegate.
AsyncDelegate dlgt = new AsyncDelegate(ad.TestMethod);
// Initiate the asychronous call.
IAsyncResult ar = dlgt.BeginInvoke(3000,out threadId, null, null);
// Poll while simulating work.
while (ar.IsCompleted == false)
{
Thread.Sleep(10);
}
// Call EndInvoke to retrieve the results.
string ret = dlgt.EndInvoke(out threadId, ar);
Console.WriteLine("The call executed on thread {0}, with return value \"{1}\".", threadId, ret);
}
}
}
運行結(jié)果：
Test method begins.
The call executed on thread 5300, with return value "MyCallTime was 3000".
請按任意鍵繼續(xù). . .
4、C#異步調(diào)用四大方法之異步調(diào)用完成時執(zhí)行回調(diào)方法
如果啟動異步調(diào)用的線程不需要處理調(diào)用結(jié)果，則可以在調(diào)用完成時執(zhí)行回調(diào)方法?；卣{(diào)方法在 ThreadPool 線程上執(zhí)行。
要使用回調(diào)方法，必須將代表該方法的 AsyncCallback 委托傳遞給 BeginInvoke。也可以傳遞包含回調(diào)方法將要使用的信息的對象。例如，可以傳遞啟動調(diào)用時曾使用的委托，以便回調(diào)方法能夠調(diào)用 EndInvoke。
view plaincopy to clipboardprint?
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;
namespace ConsoleAppAsync
{
// The delegate must have the same signature as the method
// you want to call asynchronously.
public delegate string AsyncDelegate(int callDuration, out int threadId);
public class AsyncDemo
{
// The method to be executed asynchronously.
public string TestMethod(int callDuration, out int threadId)
{
Console.WriteLine("Test method begins.");
Thread.Sleep(callDuration);
threadId = AppDomain.GetCurrentThreadId();
return "MyCallTime was " + callDuration.ToString();
}
}
class Program4
{
// Asynchronous method puts the thread id here.
private static int threadId;
static void Main(string[] args)
{
// Create an instance of the test class.
AsyncDemo ad = new AsyncDemo();
// Create the delegate.
AsyncDelegate dlgt = new AsyncDelegate(ad.TestMethod);
// Initiate the asychronous call. Include an AsyncCallback
// delegate representing the callback method, and the data
// needed to call EndInvoke.
IAsyncResult ar = dlgt.BeginInvoke(3000,out threadId, new AsyncCallback(CallbackMethod),dlgt);
Console.WriteLine("Press Enter to close application.");
Console.ReadLine();
}
// Callback method must have the same signature as the
// AsyncCallback delegate.
static void CallbackMethod(IAsyncResult ar)
{
// Retrieve the delegate.
AsyncDelegate dlgt = (AsyncDelegate)ar.AsyncState;
// Call EndInvoke to retrieve the results.
string ret = dlgt.EndInvoke(out threadId, ar);
Console.WriteLine("The call executed on thread {0}, with return value \"{1}\".", threadId, ret);
}
}
}
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;
namespace ConsoleAppAsync
{
// The delegate must have the same signature as the method
// you want to call asynchronously.
public delegate string AsyncDelegate(int callDuration, out int threadId);
public class AsyncDemo
{
// The method to be executed asynchronously.
public string TestMethod(int callDuration, out int threadId)
{
Console.WriteLine("Test method begins.");
Thread.Sleep(callDuration);
threadId = AppDomain.GetCurrentThreadId();
return "MyCallTime was " + callDuration.ToString();
}
}
class Program4
{
// Asynchronous method puts the thread id here.
private static int threadId;
static void Main(string[] args)
{
// Create an instance of the test class.
AsyncDemo ad = new AsyncDemo();
// Create the delegate.
AsyncDelegate dlgt = new AsyncDelegate(ad.TestMethod);
// Initiate the asychronous call. Include an AsyncCallback
// delegate representing the callback method, and the data
// needed to call EndInvoke.
IAsyncResult ar = dlgt.BeginInvoke(3000,out threadId, new AsyncCallback(CallbackMethod),dlgt);
Console.WriteLine("Press Enter to close application.");
Console.ReadLine();
}
// Callback method must have the same signature as the
// AsyncCallback delegate.
static void CallbackMethod(IAsyncResult ar)
{
// Retrieve the delegate.
AsyncDelegate dlgt = (AsyncDelegate)ar.AsyncState;
// Call EndInvoke to retrieve the results.
string ret = dlgt.EndInvoke(out threadId, ar);
Console.WriteLine("The call executed on thread {0}, with return value \"{1}\".", threadId, ret);
}
}
}
運行結(jié)果：
Press Enter to close application.
Test method begins.
The call executed on thread 7632, with return value "MyCallTime was 3000".
C#異步調(diào)用四大方法的基本內(nèi)容就向你介紹到這里，希望對你了解和學習C#異步調(diào)用有所幫助。
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