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深入分析C# Task

 更新時間：2020年08月05日 09:43:30   作者：五維思考  
這篇文章主要介紹了C# Task的相關(guān)資料，文中講解非常細(xì)致，代碼幫助大家更好的理解和學(xué)習(xí)C# Task的相關(guān)知識，感興趣的朋友可以了解下

​Task的MSDN的描述如下：

【Task類的表示單個操作不會返回一個值，通常以異步方式執(zhí)行。

Task對象是一種的中心思想基于任務(wù)的異步模式首次引入.NETFramework 4 中。

因為由執(zhí)行工作Task對象通常以異步方式執(zhí)行線程池線程上而不是以同步方式在主應(yīng)用程序線程中，可以使用Status屬性，并將IsCanceled， IsCompleted，和IsFaulted屬性，以確定任務(wù)的狀態(tài)。

大多數(shù)情況下，lambda 表達(dá)式用于指定該任務(wù)所執(zhí)行的工作量。

對于返回值的操作，您使用Task類?！?/p>

1、Task的優(yōu)勢

　　ThreadPool相比Thread來說具備了很多優(yōu)勢，但是ThreadPool卻又存在一些使用上的不方便。比如：

  • ThreadPool不支持線程的取消、完成、失敗通知等交互性操作；
  • ThreadPool不支持線程執(zhí)行的先后次序；

　　以往，如果開發(fā)者要實現(xiàn)上述功能，需要完成很多額外的工作，現(xiàn)在，F(xiàn)CL中提供了一個功能更強(qiáng)大的概念：Task。Task在線程池的基礎(chǔ)上進(jìn)行了優(yōu)化，并提供了更多的API。在FCL4.0中，如果我們要編寫多線程程序，Task顯然已經(jīng)優(yōu)于傳統(tǒng)的方式。

　　以下是一個簡單的任務(wù)示例：

using System;
using System.Threading;
using System.Threading.Tasks;

namespace ConsoleApp1
{
  class Program
  {
    static void Main(string[] args)
    {
      Task t = new Task(() =>
      {
        Console.WriteLine("任務(wù)開始工作……");
        //模擬工作過程
        Thread.Sleep(5000);
      });
      t.Start();
      t.ContinueWith((task) =>
      {
        Console.WriteLine("任務(wù)完成，完成時候的狀態(tài)為：");
        Console.WriteLine("IsCanceled={0}\tIsCompleted={1}\tIsFaulted={2}", task.IsCanceled, task.IsCompleted, task.IsFaulted);
      });
      Console.ReadKey();
    }
  }
}

2、Task的用法

　　2.1、創(chuàng)建任務(wù)

　?。ㄒ唬o返回值的方式

　　方式1:

　　var t1 = new Task(() => TaskMethod("Task 1"));
　　t1.Start();
　　Task.WaitAll(t1);//等待所有任務(wù)結(jié)束 
　　注:任務(wù)的狀態(tài):
　　Start之前為:Created
　　Start之后為:WaitingToRun

　　方式2:

Task.Run(() => TaskMethod("Task 2"));

　　方式3:

Task.Factory.StartNew(() => TaskMethod("Task 3")); 直接異步的方法 
　　//或者
　　var t3=Task.Factory.StartNew(() => TaskMethod("Task 3"));
　　Task.WaitAll(t3);//等待所有任務(wù)結(jié)束
　　//任務(wù)的狀態(tài):
　　Start之前為:Running
　　Start之后為:Running
using System;
using System.Threading;
using System.Threading.Tasks;

namespace ConsoleApp1
{
  class Program
  {
    static void Main(string[] args)
    {
      var t1 = new Task(() => TaskMethod("Task 1"));
      var t2 = new Task(() => TaskMethod("Task 2"));
      t2.Start();
      t1.Start();
      Task.WaitAll(t1, t2);
      Task.Run(() => TaskMethod("Task 3"));
      Task.Factory.StartNew(() => TaskMethod("Task 4"));
      //標(biāo)記為長時間運行任務(wù),則任務(wù)不會使用線程池,而在單獨的線程中運行。
      Task.Factory.StartNew(() => TaskMethod("Task 5"), TaskCreationOptions.LongRunning);

      #region 常規(guī)的使用方式
      Console.WriteLine("主線程執(zhí)行業(yè)務(wù)處理.");
      //創(chuàng)建任務(wù)
      Task task = new Task(() =>
      {
        Console.WriteLine("使用System.Threading.Tasks.Task執(zhí)行異步操作.");
        for (int i = 0; i < 10; i++)
        {
          Console.WriteLine(i);
        }
      });
      //啟動任務(wù),并安排到當(dāng)前任務(wù)隊列線程中執(zhí)行任務(wù)(System.Threading.Tasks.TaskScheduler)
      task.Start();
      Console.WriteLine("主線程執(zhí)行其他處理");
      task.Wait();
      #endregion

      Thread.Sleep(TimeSpan.FromSeconds(1));
      Console.ReadLine();
    }

    static void TaskMethod(string name)
    {
      Console.WriteLine("Task {0} is running on a thread id {1}. Is thread pool thread: {2}",
        name, Thread.CurrentThread.ManagedThreadId, Thread.CurrentThread.IsThreadPoolThread);
    }
  }
}

　　async/await的實現(xiàn)方式:

using System;
using System.Threading;
using System.Threading.Tasks;

namespace ConsoleApp1
{
  class Program
  {
    async static void AsyncFunction()
    {
      await Task.Delay(1);
      Console.WriteLine("使用System.Threading.Tasks.Task執(zhí)行異步操作.");
      for (int i = 0; i < 10; i++)
      {
        Console.WriteLine(string.Format("AsyncFunction:i={0}", i));
      }
    }

    public static void Main()
    {
      Console.WriteLine("主線程執(zhí)行業(yè)務(wù)處理.");
      AsyncFunction();
      Console.WriteLine("主線程執(zhí)行其他處理");
      for (int i = 0; i < 10; i++)
      {
        Console.WriteLine(string.Format("Main:i={0}", i));
      }
      Console.ReadLine();
    }
  }
}

　?。ǘХ祷刂档姆绞?/p>

　　方式4:

Task<int> task = CreateTask("Task 1");
task.Start(); 
int result = task.Result;
using System;
using System.Threading;
using System.Threading.Tasks;

namespace ConsoleApp1
{
  class Program
  {
    static Task<int> CreateTask(string name)
    {
      return new Task<int>(() => TaskMethod(name));
    }

    static void Main(string[] args)
    {
      TaskMethod("Main Thread Task");
      Task<int> task = CreateTask("Task 1");
      task.Start();
      int result = task.Result;
      Console.WriteLine("Task 1 Result is: {0}", result);

      task = CreateTask("Task 2");
      //該任務(wù)會運行在主線程中
      task.RunSynchronously();
      result = task.Result;
      Console.WriteLine("Task 2 Result is: {0}", result);

      task = CreateTask("Task 3");
      Console.WriteLine(task.Status);
      task.Start();

      while (!task.IsCompleted)
      {
        Console.WriteLine(task.Status);
        Thread.Sleep(TimeSpan.FromSeconds(0.5));
      }

      Console.WriteLine(task.Status);
      result = task.Result;
      Console.WriteLine("Task 3 Result is: {0}", result);

      #region 常規(guī)使用方式
      //創(chuàng)建任務(wù)
      Task<int> getsumtask = new Task<int>(() => Getsum());
      //啟動任務(wù),并安排到當(dāng)前任務(wù)隊列線程中執(zhí)行任務(wù)(System.Threading.Tasks.TaskScheduler)
      getsumtask.Start();
      Console.WriteLine("主線程執(zhí)行其他處理");
      //等待任務(wù)的完成執(zhí)行過程。
      getsumtask.Wait();
      //獲得任務(wù)的執(zhí)行結(jié)果
      Console.WriteLine("任務(wù)執(zhí)行結(jié)果：{0}", getsumtask.Result.ToString());
      #endregion
    }

    static int TaskMethod(string name)
    {
      Console.WriteLine("Task {0} is running on a thread id {1}. Is thread pool thread: {2}",
        name, Thread.CurrentThread.ManagedThreadId, Thread.CurrentThread.IsThreadPoolThread);
      Thread.Sleep(TimeSpan.FromSeconds(2));
      return 42;
    }

    static int Getsum()
    {
      int sum = 0;
      Console.WriteLine("使用Task執(zhí)行異步操作.");
      for (int i = 0; i < 100; i++)
      {
        sum += i;
      }
      return sum;
    }
  }
}

    async/await的實現(xiàn):

using System;
using System.Threading.Tasks;

namespace ConsoleApp1
{
  class Program
  {
    public static void Main()
    {
      var ret1 = AsyncGetsum();
      Console.WriteLine("主線程執(zhí)行其他處理");
      for (int i = 1; i <= 3; i++)
        Console.WriteLine("Call Main()");
      int result = ret1.Result;         //阻塞主線程
      Console.WriteLine("任務(wù)執(zhí)行結(jié)果：{0}", result);
    }

    async static Task<int> AsyncGetsum()
    {
      await Task.Delay(1);
      int sum = 0;
      Console.WriteLine("使用Task執(zhí)行異步操作.");
      for (int i = 0; i < 100; i++)
      {
        sum += i;
      }
      return sum;
    }
  }
}

　　2.2、組合任務(wù).ContinueWith

　　 簡單Demo:

using System;
using System.Threading.Tasks;

namespace ConsoleApp1
{
  class Program
  {
    public static void Main()
    {
      //創(chuàng)建一個任務(wù)
      Task<int> task = new Task<int>(() =>
      {
        int sum = 0;
        Console.WriteLine("使用Task執(zhí)行異步操作.");
        for (int i = 0; i < 100; i++)
        {
          sum += i;
        }
        return sum;
      });
      //啟動任務(wù),并安排到當(dāng)前任務(wù)隊列線程中執(zhí)行任務(wù)(System.Threading.Tasks.TaskScheduler)
      task.Start();
      Console.WriteLine("主線程執(zhí)行其他處理");
      //任務(wù)完成時執(zhí)行處理。
      Task cwt = task.ContinueWith(t =>
      {
        Console.WriteLine("任務(wù)完成后的執(zhí)行結(jié)果：{0}", t.Result.ToString());
      });
      task.Wait();
      cwt.Wait();
    }
  }
}

　　 任務(wù)的串行:

using System;
using System.Collections.Concurrent;
using System.Threading;
using System.Threading.Tasks;

namespace ConsoleApp1
{
  class Program
  {
    static void Main(string[] args)
    {
      ConcurrentStack<int> stack = new ConcurrentStack<int>();

      //t1先串行
      var t1 = Task.Factory.StartNew(() =>
      {
        stack.Push(1);
        stack.Push(2);
      });

      //t2,t3并行執(zhí)行
      var t2 = t1.ContinueWith(t =>
      {
        int result;
        stack.TryPop(out result);
        Console.WriteLine("Task t2 result={0},Thread id {1}", result, Thread.CurrentThread.ManagedThreadId);
      });

      //t2,t3并行執(zhí)行
      var t3 = t1.ContinueWith(t =>
      {
        int result;
        stack.TryPop(out result);
        Console.WriteLine("Task t3 result={0},Thread id {1}", result, Thread.CurrentThread.ManagedThreadId);
      });

      //等待t2和t3執(zhí)行完
      Task.WaitAll(t2, t3);

      //t7串行執(zhí)行
      var t4 = Task.Factory.StartNew(() =>
      {
        Console.WriteLine("當(dāng)前集合元素個數(shù)：{0},Thread id {1}", stack.Count, Thread.CurrentThread.ManagedThreadId);
      });
      t4.Wait();
    }
  }
}

　　子任務(wù):

using System;
using System.Threading.Tasks;

namespace ConsoleApp1
{
  class Program
  {
    public static void Main()
    {
      Task<string[]> parent = new Task<string[]>(state =>
      {
        Console.WriteLine(state);
        string[] result = new string[2];
        //創(chuàng)建并啟動子任務(wù)
        new Task(() => { result[0] = "我是子任務(wù)1。"; }, TaskCreationOptions.AttachedToParent).Start();
        new Task(() => { result[1] = "我是子任務(wù)2。"; }, TaskCreationOptions.AttachedToParent).Start();
        return result;
      }, "我是父任務(wù)，并在我的處理過程中創(chuàng)建多個子任務(wù)，所有子任務(wù)完成以后我才會結(jié)束執(zhí)行。");
      //任務(wù)處理完成后執(zhí)行的操作
      parent.ContinueWith(t =>
      {
        Array.ForEach(t.Result, r => Console.WriteLine(r));
      });
      //啟動父任務(wù)
      parent.Start();
      //等待任務(wù)結(jié)束 Wait只能等待父線程結(jié)束,沒辦法等到父線程的ContinueWith結(jié)束
      //parent.Wait();
      Console.ReadLine();

    }
  }
}

　　動態(tài)并行(TaskCreationOptions.AttachedToParent) 父任務(wù)等待所有子任務(wù)完成后 整個任務(wù)才算完成

using System;
using System.Threading;
using System.Threading.Tasks;

namespace ConsoleApp1
{
  class Node
  {
    public Node Left { get; set; }
    public Node Right { get; set; }
    public string Text { get; set; }
  }


  class Program
  {
    static Node GetNode()
    {
      Node root = new Node
      {
        Left = new Node
        {
          Left = new Node
          {
            Text = "L-L"
          },
          Right = new Node
          {
            Text = "L-R"
          },
          Text = "L"
        },
        Right = new Node
        {
          Left = new Node
          {
            Text = "R-L"
          },
          Right = new Node
          {
            Text = "R-R"
          },
          Text = "R"
        },
        Text = "Root"
      };
      return root;
    }

    static void Main(string[] args)
    {
      Node root = GetNode();
      DisplayTree(root);
    }

    static void DisplayTree(Node root)
    {
      var task = Task.Factory.StartNew(() => DisplayNode(root),
                      CancellationToken.None,
                      TaskCreationOptions.None,
                      TaskScheduler.Default);
      task.Wait();
    }

    static void DisplayNode(Node current)
    {

      if (current.Left != null)
        Task.Factory.StartNew(() => DisplayNode(current.Left),
                      CancellationToken.None,
                      TaskCreationOptions.AttachedToParent,
                      TaskScheduler.Default);
      if (current.Right != null)
        Task.Factory.StartNew(() => DisplayNode(current.Right),
                      CancellationToken.None,
                      TaskCreationOptions.AttachedToParent,
                      TaskScheduler.Default);
      Console.WriteLine("當(dāng)前節(jié)點的值為{0};處理的ThreadId={1}", current.Text, Thread.CurrentThread.ManagedThreadId);
    }
  }
}

　　2.3、取消任務(wù) CancellationTokenSource

using System;
using System.Threading;
using System.Threading.Tasks;

namespace ConsoleApp1
{
  class Program
  {
    private static int TaskMethod(string name, int seconds, CancellationToken token)
    {
      Console.WriteLine("Task {0} is running on a thread id {1}. Is thread pool thread: {2}",
        name, Thread.CurrentThread.ManagedThreadId, Thread.CurrentThread.IsThreadPoolThread);
      for (int i = 0; i < seconds; i++)
      {
        Thread.Sleep(TimeSpan.FromSeconds(1));
        if (token.IsCancellationRequested) return -1;
      }
      return 42 * seconds;
    }

    private static void Main(string[] args)
    {
      var cts = new CancellationTokenSource();
      var longTask = new Task<int>(() => TaskMethod("Task 1", 10, cts.Token), cts.Token);
      Console.WriteLine(longTask.Status);
      cts.Cancel();
      Console.WriteLine(longTask.Status);
      Console.WriteLine("First task has been cancelled before execution");
      cts = new CancellationTokenSource();
      longTask = new Task<int>(() => TaskMethod("Task 2", 10, cts.Token), cts.Token);
      longTask.Start();
      for (int i = 0; i < 5; i++)
      {
        Thread.Sleep(TimeSpan.FromSeconds(0.5));
        Console.WriteLine(longTask.Status);
      }
      cts.Cancel();
      for (int i = 0; i < 5; i++)
      {
        Thread.Sleep(TimeSpan.FromSeconds(0.5));
        Console.WriteLine(longTask.Status);
      }

      Console.WriteLine("A task has been completed with result {0}.", longTask.Result);
    }
  }
}

　　2.4、處理任務(wù)中的異常

　　單個任務(wù):

using System;
using System.Threading;
using System.Threading.Tasks;

namespace ConsoleApp1
{
  class Program
  {
    static int TaskMethod(string name, int seconds)
    {
      Console.WriteLine("Task {0} is running on a thread id {1}. Is thread pool thread: {2}",
        name, Thread.CurrentThread.ManagedThreadId, Thread.CurrentThread.IsThreadPoolThread);
      Thread.Sleep(TimeSpan.FromSeconds(seconds));
      throw new Exception("Boom!");
      return 42 * seconds;
    }

    static void Main(string[] args)
    {
      try
      {
        Task<int> task = Task.Run(() => TaskMethod("Task 2", 2));
        int result = task.GetAwaiter().GetResult();
        Console.WriteLine("Result: {0}", result);
      }
      catch (Exception ex)
      {
        Console.WriteLine("Task 2 Exception caught: {0}", ex.Message);
      }
      Console.WriteLine("----------------------------------------------");
      Console.WriteLine();
    }
  }
}

　　多個任務(wù):

using System;
using System.Threading;
using System.Threading.Tasks;

namespace ConsoleApp1
{
  class Program
  {
    static int TaskMethod(string name, int seconds)
    {
      Console.WriteLine("Task {0} is running on a thread id {1}. Is thread pool thread: {2}",
        name, Thread.CurrentThread.ManagedThreadId, Thread.CurrentThread.IsThreadPoolThread);
      Thread.Sleep(TimeSpan.FromSeconds(seconds));
      throw new Exception(string.Format("Task {0} Boom!", name));
      return 42 * seconds;
    }


    public static void Main(string[] args)
    {
      try
      {
        var t1 = new Task<int>(() => TaskMethod("Task 3", 3));
        var t2 = new Task<int>(() => TaskMethod("Task 4", 2));
        var complexTask = Task.WhenAll(t1, t2);
        var exceptionHandler = complexTask.ContinueWith(t =>
            Console.WriteLine("Result: {0}", t.Result),
            TaskContinuationOptions.OnlyOnFaulted
          );
        t1.Start();
        t2.Start();
        Task.WaitAll(t1, t2);
      }
      catch (AggregateException ex)
      {
        ex.Handle(exception =>
        {
          Console.WriteLine(exception.Message);
          return true;
        });
      }
    }
  }
}

    async/await的方式:

using System;
using System.Threading;
using System.Threading.Tasks;

namespace ConsoleApp1
{
  class Program
  {
    static async Task ThrowNotImplementedExceptionAsync()
    {
      throw new NotImplementedException();
    }

    static async Task ThrowInvalidOperationExceptionAsync()
    {
      throw new InvalidOperationException();
    }

    static async Task Normal()
    {
      await Fun();
    }

    static Task Fun()
    {
      return Task.Run(() =>
      {
        for (int i = 1; i <= 10; i++)
        {
          Console.WriteLine("i={0}", i);
          Thread.Sleep(200);
        }
      });
    }

    static async Task ObserveOneExceptionAsync()
    {
      var task1 = ThrowNotImplementedExceptionAsync();
      var task2 = ThrowInvalidOperationExceptionAsync();
      var task3 = Normal();


      try
      {
        //異步的方式
        Task allTasks = Task.WhenAll(task1, task2, task3);
        await allTasks;
        //同步的方式
        //Task.WaitAll(task1, task2, task3);
      }
      catch (NotImplementedException ex)
      {
        Console.WriteLine("task1 任務(wù)報錯!");
      }
      catch (InvalidOperationException ex)
      {
        Console.WriteLine("task2 任務(wù)報錯!");
      }
      catch (Exception ex)
      {
        Console.WriteLine("任務(wù)報錯!");
      }

    }

    public static void Main()
    {
      Task task = ObserveOneExceptionAsync();
      Console.WriteLine("主線程繼續(xù)運行........");
      task.Wait();
    }
  }
}

　　2.5、Task.FromResult的應(yīng)用

using System;
using System.Collections.Generic;
using System.Threading;
using System.Threading.Tasks;

namespace ConsoleApp1
{
  class Program
  {
    static IDictionary<string, string> cache = new Dictionary<string, string>()
    {
      {"0001","A"},
      {"0002","B"},
      {"0003","C"},
      {"0004","D"},
      {"0005","E"},
      {"0006","F"},
    };

    public static void Main()
    {
      Task<string> task = GetValueFromCache("0006");
      Console.WriteLine("主程序繼續(xù)執(zhí)行。。。。");
      string result = task.Result;
      Console.WriteLine("result={0}", result);

    }

    private static Task<string> GetValueFromCache(string key)
    {
      Console.WriteLine("GetValueFromCache開始執(zhí)行。。。。");
      string result = string.Empty;
      //Task.Delay(5000);
      Thread.Sleep(5000);
      Console.WriteLine("GetValueFromCache繼續(xù)執(zhí)行。。。。");
      if (cache.TryGetValue(key, out result))
      {
        return Task.FromResult(result);
      }
      return Task.FromResult("");
    }

  }
}

　　2.6、使用IProgress實現(xiàn)異步編程的進(jìn)程通知

　　IProgress<in T>只提供了一個方法void Report(T value)，通過Report方法把一個T類型的值報告給IProgress,然后IProgress<in T>的實現(xiàn)類Progress<in T>的構(gòu)造函數(shù)接收類型為Action<T>的形參，通過這個委托讓進(jìn)度顯示在UI界面中。

using System;
using System.Threading;
using System.Threading.Tasks;

namespace ConsoleApp1
{
  class Program
  {
    static void DoProcessing(IProgress<int> progress)
    {
      for (int i = 0; i <= 100; ++i)
      {
        Thread.Sleep(100);
        if (progress != null)
        {
          progress.Report(i);
        }
      }
    }

    static async Task Display()
    {
      //當(dāng)前線程
      var progress = new Progress<int>(percent =>
      {
        Console.Clear();
        Console.Write("{0}%", percent);
      });
      //線程池線程
      await Task.Run(() => DoProcessing(progress));
      Console.WriteLine("");
      Console.WriteLine("結(jié)束");
    }

    public static void Main()
    {
      Task task = Display();
      task.Wait();
    }
  }
}

　　2.7、Factory.FromAsync的應(yīng)用 (簡APM模式(委托)轉(zhuǎn)換為任務(wù))(BeginXXX和EndXXX)

　　帶回調(diào)方式的

using System;
using System.Threading;
using System.Threading.Tasks;

namespace ConsoleApp1
{
  class Program
  {
    private delegate string AsynchronousTask(string threadName);

    private static string Test(string threadName)
    {
      Console.WriteLine("Starting...");
      Console.WriteLine("Is thread pool thread: {0}", Thread.CurrentThread.IsThreadPoolThread);
      Thread.Sleep(TimeSpan.FromSeconds(2));
      Thread.CurrentThread.Name = threadName;
      return string.Format("Thread name: {0}", Thread.CurrentThread.Name);
    }

    private static void Callback(IAsyncResult ar)
    {
      Console.WriteLine("Starting a callback...");
      Console.WriteLine("State passed to a callbak: {0}", ar.AsyncState);
      Console.WriteLine("Is thread pool thread: {0}", Thread.CurrentThread.IsThreadPoolThread);
      Console.WriteLine("Thread pool worker thread id: {0}", Thread.CurrentThread.ManagedThreadId);
    }

    //執(zhí)行的流程是 先執(zhí)行Test--->Callback--->task.ContinueWith
    static void Main(string[] args)
    {
      AsynchronousTask d = Test;
      Console.WriteLine("Option 1");
      Task<string> task = Task<string>.Factory.FromAsync(
        d.BeginInvoke("AsyncTaskThread", Callback, "a delegate asynchronous call"), d.EndInvoke);

      task.ContinueWith(t => Console.WriteLine("Callback is finished, now running a continuation! Result: {0}",
        t.Result));

      while (!task.IsCompleted)
      {
        Console.WriteLine(task.Status);
        Thread.Sleep(TimeSpan.FromSeconds(0.5));
      }
      Console.WriteLine(task.Status);

    }
  }
}

　　不帶回調(diào)方式的

using System;
using System.Threading;
using System.Threading.Tasks;

namespace ConsoleApp1
{
  class Program
  {
    private delegate string AsynchronousTask(string threadName);

    private static string Test(string threadName)
    {
      Console.WriteLine("Starting...");
      Console.WriteLine("Is thread pool thread: {0}", Thread.CurrentThread.IsThreadPoolThread);
      Thread.Sleep(TimeSpan.FromSeconds(2));
      Thread.CurrentThread.Name = threadName;
      return string.Format("Thread name: {0}", Thread.CurrentThread.Name);
    }

    //執(zhí)行的流程是 先執(zhí)行Test--->task.ContinueWith
    static void Main(string[] args)
    {
      AsynchronousTask d = Test;
      Task<string> task = Task<string>.Factory.FromAsync(
        d.BeginInvoke, d.EndInvoke, "AsyncTaskThread", "a delegate asynchronous call");
      task.ContinueWith(t => Console.WriteLine("Task is completed, now running a continuation! Result: {0}",
        t.Result));
      while (!task.IsCompleted)
      {
        Console.WriteLine(task.Status);
        Thread.Sleep(TimeSpan.FromSeconds(0.5));
      }
      Console.WriteLine(task.Status);

    }
  }
}
//Task啟動帶參數(shù)和返回值的函數(shù)任務(wù)
//下面的例子test2 是個帶參數(shù)和返回值的函數(shù)。

private int test2(object i)
{
  this.Invoke(new Action(() =>
  {
    pictureBox1.Visible = true;
  }));
  System.Threading.Thread.Sleep(3000);
  MessageBox.Show("hello:" + i);
  this.Invoke(new Action(() =>
  {
    pictureBox1.Visible = false;
  }));
  return 0;
}

//測試調(diào)用
private void call()
{
  //Func<string, string> funcOne = delegate(string s){ return "fff"; };
  object i = 55;
  var t = Task<int>.Factory.StartNew(new Func<object, int>(test2), i);
}

//= 下載網(wǎng)站源文件例子 == == == == == == == == == == == ==
//HttpClient 引用System.Net.Http
private async Task< int> test2(object i)
{
  this.Invoke(new Action(() =>
  {
    pictureBox1.Visible = true;
  }));

  HttpClient client = new HttpClient();
  var a = await client.GetAsync("http://www.baidu.com");
  Task<string> s = a.Content.ReadAsStringAsync();
  MessageBox.Show (s.Result);

  //System.Threading.Thread.Sleep(3000);
  //MessageBox.Show("hello:"+ i);
  this.Invoke(new Action(() =>
  {
    pictureBox1.Visible = false;
  }));
  return 0;
}

async private void call()
{
  //Func<string, string> funcOne = delegate(string s){ return "fff"; };
  object i = 55;
  var t = Task<Task<int>>.Factory.StartNew(new Func<object, Task<int>>(test2), i);
}

//----------或者----------

private async void test2()
{
  this.Invoke(new Action(() =>
  {
    pictureBox1.Visible = true;
  }));
  HttpClient client = new HttpClient();
  var a = await client.GetAsync("http://www.baidu.com");
  Task<string> s = a.Content.ReadAsStringAsync();
  MessageBox.Show (s.Result);
  this.Invoke(new Action(() =>
  {
    pictureBox1.Visible = false;
  }));
}

private void call()
{
  var t = Task.Run(new Action(test2));
  //相當(dāng)于
  //Thread th= new Thread(new ThreadStart(test2));
  //th.Start();
}

Task啟動帶參數(shù)和返回值的函數(shù)任務(wù)

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