Windows Phone 7 异步编程模型.doc

本文由麦可网整理，转载请注明出处Windows Phone 7 异步编程模型Windows Phone 7上的异步编程模型其实也就是说把C#里面的异步编程模型在Windows Phone 7应用开发上使用。下面来看一下异步编程模型里面的一些关键的概念。2个方法和一个委托和一个接口：(1)BeginInvoke方法用于启动异步调用Begin 方法包含同步方法签名中的任何参数，此外还包含另外两个参数：一个AsyncCallback 委托和一个用户定义的状态对象。委托用来调用回调方法，状态对象是用来向回调方法传递状态信息。BeginInvoke立即返回，不等待异步调用完成。BeginInvoke返回IasyncResult，可用于监视调用进度。(2)EndInvoke方法用于检索异步调用结果。End 方法用于结束异步操作并返回结果，因此包含同步方法签名中的 ref 和 out 参数，返回值类型也与同步方法相同。该方法还包括一个 IAsyncResult 参数，用于获取异步操作是否完成的信息，当然在使用时就必须传入对应的 Begin 方法返回的对象实例开始异步操作后如果要阻止应用程序，可以直接调用 End 方法，这会阻止应用程序直到异步操作完成后再继续执行。也可以使用 IAsyncResult 的 AsyncWaitHandle 属性，调用其中的WaitOne等方法来阻塞线程。这两种方法的区别不大，只是前者必须一直等待而后者可以设置等待超时。如果不阻止应用程序，则可以通过轮循 IAsyncResult 的 IsCompleted 状态来判断操作是否完成，或使用 AsyncCallback 委托来结束异步操作。AsyncCallback 委托包含一个 IAsyncResult 的签名，回调方法内部再调用 End 方法来获取操作执行结果。在调用BeginInvoke后可随时调用EndInvoke方法,注意：始终在异步调用完成后调用EndInvoke.如果异步调用未完成，EndInvoke将一直阻塞到异步调用完成。EndInvoke的参数包括需要异步执行的方法的out和ref参数以及由BeginInvoke返回的IAsyncResult。要注意的是,始终在异步调用完成后调用EndInvoke(3)AsyncCallback委托用于指定在开始操作完成后应被调用的方法AsyncCallback委托被作为开始操作上的第二个到最后一个参数传递代码原型如下：Serializablepublic delegate void AsyncCallback(IAsyncResult ar);(4)IAsyncResult接口它表示异步操作的状态.该接口定义了4个公用属性public interface IAsyncResult object AsyncState get; WaitHandle AsyncWaitHandle get; bool CompletedSynchronously get; bool IsCompleted get; 在Windows Phone 7上的应用AsyncResultNoResult.csusing 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; / / 初始化 / / 异步返回方法 / 异步调用对象 public AsyncResultNoResult(AsyncCallback asyncCallback, object state) this._asyncCallback = asyncCallback; this._asyncState = state; / / 结束任务 / public void EndInvoke() / This method assumes that only 1 thread calls EndInvoke / for this object if (!this.IsCompleted)/任务未完成 / If the operation isnt done, wait for it this.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 case this._exception = exception; / The m_CompletedState field MUST be set prior calling the callback if (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 it this._asyncWaitHandle.Set(); if (this._asyncCallback != null) / If a callback method was set, call it this._asyncCallback(this);/调用异步请求的返回方法 / / 放弃异步请求的对象 / 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(ref this._asyncWaitHandle, event2, null) != null) / Another thread created this objects event; dispose / the event we just created event2.Close(); else if (!isCompleted & this.IsCompleted) / If the operation wasnt 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); AsyncResult.csusing System;namespace AsyncTaskDemo public class AsyncResult : 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); / / 停止异步返回返回对象 / / public TResult EndInvoke() base.EndInvoke(); /等待操作完成 return m_result; / 返回结果 / / 操作完成 / / 返回结果对象 / 是否同步操作 public void SetAsCompleted(TResult result, bool completedSynchronously) /保存异步操作的结果 m_result = result; base.SetAsCompleted(null, completedSynchronously); TestTask.csusing System;using System.Threading;namespace AsyncTaskDemo public class TestTask public TestTask() public IAsyncResult BeginTestTask(string text, AsyncCallback asyncCallback, object state) AsyncResult asyncResult = new AsyncResult(asyncCallback, state); ThreadPool.QueueUserWorkItem(DoTestTask, asyncResult); return asyncResult; public string EndTestTask(IAsyncResult asyncResult) return (AsyncResult)asyncResult).EndInvoke(); private void DoTestTask(Object asyncResult) AsyncResult ar = (AsyncResult)asyncResult; try Thread.Sleep(3000); ar.SetAsCompleted(测试完成, true); catch (Exception e) ar.SetAsCompleted(e, false); MainPage.xaml.csTestTask tt = new TestTask(); WebTask webTask = new WebTask(new Uri(/linzheng); IAsyncResult ia; public MainPage() InitializeComponent(); private void button1_Click(object sender, RoutedEventArgs e) Funcstring, IObservable testResult = Obs