【温故知新】C#基于事件的异步模式（EAP）

this.button1.Click += new System.EventHandler(this.button1_Click);

private void button1_Click(object sender, EventArgs e)
{
//dosomething
}

public class Downloader
{ //声明事件参数
public class DownloadCompletedEventArgs : System.ComponentModel.AsyncCompletedEventArgs
{
private string m_result;
public DownloadCompletedEventArgs(string result, Exception error, bool cancelled, Object userState)
: base(error, cancelled, userState)
{
m_result = result;
}
public string Result
{
get
{
//只读属性在返回属性值之前应调用 RaiseExceptionIfNecessary 方法。 如果组件的异步辅助代码将某一异常指定给 Error 属性或将 Cancelled 属性设置为 true，则该属性将在客户端尝试读取它的值时引发异常。 这会防止客户端因异步操作失败而访问可能无效的属性。
RaiseExceptionIfNecessary();
return m_result;
}
}
} //声明委托
public delegate void ProgressChangedEventHandler(
ProgressChangedEventArgs e);//ProgressChangedEventArgs自带有了。 public delegate void DownloadCompletedEventHandler(object sender,
DownloadCompletedEventArgs e); //内部下载处理委托
private delegate string DownLoadHandler(string url, string name, AsyncOperation asyncOp); //声明事件
public event ProgressChangedEventHandler ProgressChanged;
public event DownloadCompletedEventHandler DownloadCompleted; //声明SendOrPostCallback委托,通过AsyncOperation.post会将这些调用正确地封送到应用程序模型的合适线程或上下文。
private SendOrPostCallback onProgressChangedDelegate;
private SendOrPostCallback onDownloadCompletedDelegate; /// <summary>
/// 构造函数
/// </summary>
public Downloader()
{
onProgressChangedDelegate = new SendOrPostCallback(onProgressChanged);
onDownloadCompletedDelegate = new SendOrPostCallback(onDownloadComplete);
} /// <summary>
/// 通过AsyncOperation调用onProgressChangedDelegate委托关联该函数，保证运行在合适线程
/// </summary>
/// <param name="state"></param>
private void onProgressChanged(object state)
{
if (ProgressChanged != null)
{
ProgressChangedEventArgs e =
state as ProgressChangedEventArgs;
ProgressChanged(e);
}
} private void onDownloadComplete(object state)
{
if (DownloadCompleted != null)
{
DownloadCompletedEventArgs e =
state as DownloadCompletedEventArgs;
DownloadCompleted(this, e);
}
} /// <summary>
/// 异步下载文件
/// </summary>
/// <param name="url"></param>
/// <param name="name"></param>
public void DownloadAsync(string url, string name)
{ //url不能为null
if (url == null)
{
throw new ArgumentNullException("url");
} //userSuppliedState 参数来唯一地标识每个调用，以便区分执行异步操作的过程中所引发的事件。
//不唯一的任务 ID 可能会导致您的实现无法正确报告进度和其他事件。 代码中应检查是否存在不唯一的任务 ID，并且在检测到不唯一的任务 ID 时引发 SystemArgumentException。
//由于我们不用监控异步操作状态，所以参数设为null
AsyncOperation asyncOp = AsyncOperationManager.CreateOperation(null); //异步委托调用download，如果不想再声明DownLoadHandler委托，用Action或Fun代替也行。
DownLoadHandler dh = new DownLoadHandler(DownLoad);
dh.BeginInvoke("http://pan.baidu.com/movie.avi", "乔布斯传", asyncOp, new AsyncCallback(DownloadCallBack), asyncOp);
} private void DownloadCallBack(IAsyncResult iar)
{
AsyncResult aresult = (AsyncResult)iar;
DownLoadHandler dh = aresult.AsyncDelegate as DownLoadHandler;
string r = dh.EndInvoke(iar);
AsyncOperation ao = iar.AsyncState as AsyncOperation;
//特定任务调用此方法后，再调用其相应的 AsyncOperation 对象会引发异常。
ao.PostOperationCompleted(onDownloadCompletedDelegate, new DownloadCompletedEventArgs(r, null, false, null));
} /// <summary>
/// 提供给外部调用的同步方法
/// </summary>
/// <param name="url"></param>
/// <param name="name"></param>
/// <returns></returns>
public string DownLoad(string url, string name)
{
return DownLoad(url, name, null);
} private string DownLoad(string url, string name, AsyncOperation asyncOp)
{
//url不能为null
if (url == null)
{
throw new ArgumentNullException("url");
}
for (int i = ; i < ; i++)
{
int p = i * ;
Debug.WriteLine("执行线程:" + Thread.CurrentThread.ManagedThreadId + "，传输进度：" + p + "%");
Thread.Sleep();
//不为空则是异步
if (asyncOp != null)
{
//在适合于应用程序模型的线程或上下文中调用委托。
asyncOp.Post(onProgressChangedDelegate, new ProgressChangedEventArgs(p, null));
}
}
return name + "文件下载完成！";
} }

private async void button1_Click_1(object sender, EventArgs e)
{
Downloader downloader = new Downloader();
downloader.DownloadCompleted += downloader_DownloadCompleted;
downloader.ProgressChanged += downloader_ProgressChanged;
Debug.WriteLine("调用线程:" + Thread.CurrentThread.ManagedThreadId); //异步调用
downloader.DownloadAsync("http://baidu.com", "乔布斯传.avi"); //同步调用,UI线程卡死
//string r = downloader.DownLoad("http://baidu.com", "乔布斯传.avi");
//textBox1.AppendText(r);
} void downloader_ProgressChanged(ProgressChangedEventArgs e)
{
textBox1.AppendText(("事件回调线程:" + Thread.CurrentThread.ManagedThreadId + "下载了" + e.ProgressPercentage + "%\n"));
} void downloader_DownloadCompleted(object sender, Downloader.DownloadCompletedEventArgs e)
{
textBox1.AppendText(("事件回调线程:" + Thread.CurrentThread.ManagedThreadId + "下载完成，文件为" + e.Result + "\n"));
}

public async void DownloadTaskAsync(string url, string name)
{
AsyncOperation asyncOp = AsyncOperationManager.CreateOperation(null);
string r = await Task<string>.Run(() =>
{
return DownLoad(url, name, asyncOp);
});
if (DownloadCompleted != null)
{
DownloadCompletedEventArgs e = new DownloadCompletedEventArgs(r, null, false, null);
DownloadCompleted(this, e);
}
}