using System;
using System.Threading;namespace AsyncTaskDemo
{public class AsyncResultNoResult : IAsyncResult{private readonly AsyncCallback _asyncCallback;//异步请求的返回方法private readonly object _asyncState;//异步请求的对象private ManualResetEvent _asyncWaitHandle;//线程阻塞private Exception _exception;//操作异常private int _completedState;//完成状态private const int StateCompletedAsynchronously = 2;//异步完成private const int StateCompletedSynchronously = 1;//同步完成private const int StatePending = 0;/// <summary>/// 初始化/// </summary>/// <param name="asyncCallback">异步返回方法</param>/// <param name="state">异步调用对象</param>public AsyncResultNoResult(AsyncCallback asyncCallback, object state){this._asyncCallback = asyncCallback;this._asyncState = state;}/// <summary>/// 结束任务/// </summary>public void EndInvoke(){// This method assumes that only 1 thread calls EndInvoke // for this objectif (!this.IsCompleted)//任务未完成
            {// If the operation isn't done, wait for itthis.AsyncWaitHandle.WaitOne();this.AsyncWaitHandle.Close();this._asyncWaitHandle = null; // Allow early GC
            }if (this._exception != null){RethrowException(this._exception);}}private static void RethrowException(Exception ex){throw ex;}public void SetAsCompleted(Exception exception, bool completedSynchronously){// Passing null for exception means no error occurred. // This is the common casethis._exception = exception;// The m_CompletedState field MUST be set prior calling the callbackif (Interlocked.Exchange(ref this._completedState, completedSynchronously ? 1 : 2) != 0){throw new InvalidOperationException("You can set a result only once", exception);}if (this._asyncWaitHandle != null){// If the event exists, set itthis._asyncWaitHandle.Set();}if (this._asyncCallback != null){// If a callback method was set, call itthis._asyncCallback(this);//调用异步请求的返回方法
            }}/// <summary>/// 放弃异步请求的对象/// </summary>public object AsyncState{get{return this._asyncState;}}public WaitHandle AsyncWaitHandle{get{if (this._asyncWaitHandle == null){bool isCompleted = this.IsCompleted;ManualResetEvent event2 = new ManualResetEvent(isCompleted);if (Interlocked.CompareExchange<ManualResetEvent>(ref this._asyncWaitHandle, event2, null) != null){// Another thread created this object's event; dispose // the event we just created
                        event2.Close();}else if (!isCompleted && this.IsCompleted){// If the operation wasn't done when we created // the event but now it is done, set the event//如果操作已经完成则释放阻塞this._asyncWaitHandle.Set();}}return this._asyncWaitHandle;}}//同步操作是否已经完成public bool CompletedSynchronously{get{return (this._completedState == 1);}}//是否已经完成public bool IsCompleted{get{return (this._completedState != 0);}}}
}

using System;namespace AsyncTaskDemo
{public class AsyncResult<TResult> : AsyncResultNoResult{private TResult m_result;//异步操作完成返回的对象public AsyncResult(AsyncCallback asyncCallback, object state): base(asyncCallback, state){this.m_result = default(TResult);}/// <summary>/// 停止异步返回返回对象/// </summary>/// <returns></returns>public TResult EndInvoke(){base.EndInvoke(); //等待操作完成 return m_result;  // 返回结果
        }/// <summary>/// 操作完成/// </summary>/// <param name="result">返回结果对象</param>/// <param name="completedSynchronously">是否同步操作</param>public void SetAsCompleted(TResult result, bool completedSynchronously){//保存异步操作的结果m_result = result;base.SetAsCompleted(null, completedSynchronously);}}
}

using System;
using System.Threading;namespace AsyncTaskDemo
{public class TestTask{public TestTask(){}public IAsyncResult BeginTestTask(string text, AsyncCallback asyncCallback, object state){AsyncResult<string> asyncResult = new AsyncResult<string>(asyncCallback, state);ThreadPool.QueueUserWorkItem(DoTestTask, asyncResult);return asyncResult;}public string EndTestTask(IAsyncResult asyncResult){return ((AsyncResult<string>)asyncResult).EndInvoke();}private void DoTestTask(Object asyncResult){AsyncResult<string> ar = (AsyncResult<string>)asyncResult;try{Thread.Sleep(3000);ar.SetAsCompleted("测试完成", true);}catch (Exception e){ar.SetAsCompleted(e, false);}}}
}

TestTask tt = new TestTask();WebTask webTask = new WebTask(new Uri("http://www.cnblogs.com/linzheng"));IAsyncResult ia;public MainPage(){InitializeComponent();}private void button1_Click(object sender, RoutedEventArgs e){Func<string, IObservable<string>> testResult = Observable.FromAsyncPattern<string, string>(tt.BeginTestTask, tt.EndTestTask);ObservableExtensions.Subscribe<string>(Observable.ObserveOnDispatcher<string>(testResult.Invoke("")),delegate(string success){MessageBox.Show(success);},delegate(Exception exception){MessageBox.Show(exception.Message);});}