silverlight文件下载

 

4：首先在前台添加下载按钮代码：   

<Button Content="使用WebRequest来下载" Click="Download_Click" />   

  

 

   后台代码如下：  

private void Download_Click(object sender, RoutedEventArgs e){    string filePath = "http://localhost:34270/ClientBin/test.rar";    WebRequest request = WebRequest.Create(filePath);    request.BeginGetResponse((responseAsyncCallBack) =>    {        SaveFileDialog sfd = new SaveFileDialog();        string extension = System.IO.Path.GetExtension(filePath);        sfd.Filter = string.Format("*{0}| *{0}", extension);        if (sfd.ShowDialog() == true)        {            Stream openFileStream = sfd.OpenFile();            #region 获取response bytes            WebResponse response = request.EndGetResponse(responseAsyncCallBack);            Stream responseStream = response.GetResponseStream();            Byte[] bufferBytes = new Byte[responseStream.Length];            responseStream.Read(bufferBytes, 0, bufferBytes.Length);            #endregion            openFileStream.Write(bufferBytes, 0, bufferBytes.Length);            openFileStream.Flush();        }    }, null);}

 

因为request.BeginGetResponse是异步的，所以在获取Response之后再弹出保存按钮。   

  

聪明的你能看出这段代码的问题吗？？

运行结果如下：   

   

错误是只能对UI线程执行操作，难道需要使用BeginInvoke？？  

 

OK，修改代码：   

                request.BeginGetResponse((responseAsyncCallBack) =>   

                {   

                    this.Dispatcher.BeginInvoke(() =>   

                        { //code});   

                }, null);   

  

  

 

继续运行,结果如下：   

  

 

   

  

 

情况是这样的，微软为了保证对话框必须由用户启动，所以任何尝试使用委托，或代码的方式来弹出对话框都会抛出SecurityException.   

  

 

那么如何做呢？       

  

首先SaveFileDialog必须在Download_Click事件里面，这样才不会抛出SecurityException.   

所以在WebRequest request = WebRequest.Create(filePath);的后面增加代码：   

 

//判断是否需要下载 bool needDownload = false; SaveFileDialog sfd = new SaveFileDialog(); string extension = System.IO.Path.GetExtension(filePath); sfd.Filter = string.Format("*{0}| *{0}", extension); if (sfd.ShowDialog() == true) {     needDownload = true; }

接着修改BeginGetResponse，在needDownload为true的时候开始下载文件：   

  

if (needDownload)                {                    request.BeginGetResponse((responseAsyncCallBack) =>                        {                            this.Dispatcher.BeginInvoke(() =>                                {                                    using (Stream openFileStream = sfd.OpenFile())                                    {                                        #region 获取response bytes                                            WebResponse response = request.EndGetResponse(responseAsyncCallBack);                                        Stream responseStream = response.GetResponseStream();                                            Byte[] bufferBytes = new Byte[responseStream.Length];                                        responseStream.Read(bufferBytes, 0, bufferBytes.Length);                                            #endregion                                            openFileStream.Write(bufferBytes, 0, bufferBytes.Length);                                        openFileStream.Flush();                                    }                                });                        }, null);                }    

 

完整的代码如下：   

  

 

///<summary>            ///下载按钮点击事件        ///</summary>            private void Download_Click(object sender, RoutedEventArgs e)            {                string filePath = "http://localhost:34270/ClientBin/test.rar";                WebRequest request = WebRequest.Create(filePath);                 //判断是否需要下载            bool needDownload = false;                SaveFileDialog sfd = new SaveFileDialog();                string extension = System.IO.Path.GetExtension(filePath);                sfd.Filter = string.Format("*{0}| *{0}", extension);                 if (sfd.ShowDialog() == true)                {                    needDownload = true;                }                 if (needDownload)                {                    request.BeginGetResponse((responseAsyncCallBack) =>                        {                            this.Dispatcher.BeginInvoke(() =>                                {                                    using (Stream openFileStream = sfd.OpenFile())                                    {                                        #region 获取response bytes                                        WebResponse response = request.EndGetResponse(responseAsyncCallBack);                                        Stream responseStream = response.GetResponseStream();                                        Byte[] bufferBytes = new Byte[responseStream.Length];                                        responseStream.Read(bufferBytes, 0, bufferBytes.Length);                                        #endregion                                        openFileStream.Write(bufferBytes, 0, bufferBytes.Length);                                        openFileStream.Flush();                                    }                                });                        }, null);                }            } 

 转载自：http://www.cnblogs.com/LoveJenny/archive/2011/07/10/2102114.html