Silverlight中我们很多时候需要上传下载数据的时候，在本节将讲述使用WebClient上传String、下载String、上传Stream流、下载Stream流的4个方法和相应的事件。下面我们首先认识一下WebClient类。
WebClient的主要函数如下：
•OpenReadAsync 打开流向指定资源的可读流。
•OpenWriteAsync 打开一个流以将数据写入指定的资源。这些方法不会阻止调用线程。
•DownloadStringAsync 以字符串形式下载位于指定 Uri 的资源。
•UploadStringAsync 将指定的字符串上载到指定的资源。这些方法不会阻止调用线程。
WebClient的主要事件如下：
•OpenReadCompleted 在异步资源读取操作完成时发生。
•OpenWriteCompleted 在打开流以将数据写入资源的异步操作完成时发生。
•DownloadStringCompleted 在异步资源下载操作完成时发生。
•DownloadProgressChanged 在异步下载操作成功传输部分或全部数据后发生。
•UploadStringCompleted 在异步字符串上载操作完成时发生。
•UploadProgressChanged 在异步上载操作成功转换部分或全部数据后发生。
上面的函数和事件在Silverlight的API中有详细的解释，在本文中不再复述。下面我们来看看一个实例来使用WebClient上传String、下载String、上传Stream流、下载Stream流。
首先我们准备XAML文件的前台代码，其内有四个按钮，分别代表上传String、下载String、上传Stream流、下载Stream流的按钮。代码如下：
< Grid x:Name = " LayoutRoot " Background = " White " >
< Canvas Name = " lRoot " ></ Canvas >
< Button Content = " WebClient下载XAP " Height = " 23 " HorizontalAlignment = " Left " Margin = " 410,60,0,0 " Name = " button1 " VerticalAlignment = " Top " Width = " 178 " Click = " buttonOpenReadAsync_Click " />
< Button Content = " DownloadStringAsync下载XML " Height = " 23 " HorizontalAlignment = " Left " Margin = " 410,100,0,0 " Name = " button2 " VerticalAlignment = " Top " Width = " 178 " Click = " buttonDownloadStringAsync_Click " />
< Button Content = " UploadStringAsync上传String " Height = " 23 " HorizontalAlignment = " Left " Margin = " 410,140,0,0 " Name = " button3 " VerticalAlignment = " Top " Width = " 178 " Click = " buttonUploadStringAsync_Click " />
< Button Content = " OpenWriteAsync上传图片 " Height = " 23 " HorizontalAlignment = " Left " Margin = " 410,180,0,0 " Name = " button4 " VerticalAlignment = " Top " Width = " 178 " Click = " buttonOpenWriteAsync_Click " />
</ Grid >
•上传String操作如下：
首先建立一个TestHandle.ashx,向这个文件内部写入以下代码以接收Silverlight中上传的String字符。
/// <summary>
/// TestHandle 的摘要说明
/// </summary>
public class TestHandle : IHttpHandler
{
public void ProcessRequest(HttpContext context)
{
int bytelength = context.Request.ContentLength;
byte [] inputbytes = context.Request.BinaryRead(bytelength);
string message = System.Text.Encoding.Default.GetString(inputbytes);
context.Response.ContentType = " text/plain " ;
context.Response.Write( " 你已经提交数据： " + message);
}
public bool IsReusable
{
get
{
return false ;
}
}
}
我们再看Silverlight端代码如下：
#region UploadStringAsync上传String
private void buttonUploadStringAsync_Click( object sender, RoutedEventArgs e)
{
// 开始调用UploadStringAsync异步上传String
Appclient.UploadStringAsync( new Uri( " http://localhost:3993/TestHandle.ashx " , UriKind.RelativeOrAbsolute), " <TD></TD> " );
Appclient.UploadStringCompleted += new UploadStringCompletedEventHandler(Appclient_UploadStringCompleted);
}
void Appclient_UploadStringCompleted( object sender, UploadStringCompletedEventArgs e)
{
MessageBox.Show(e.Result);
Appclient.UploadStringCompleted -= new UploadStringCompletedEventHandler(Appclient_UploadStringCompleted);
}
#endregion
•下载String操作如下：
下载ClientBin目录下已经存在的XML文件
#region DownloadStringAsync下载XML
private void buttonDownloadStringAsync_Click( object sender, RoutedEventArgs e)
{
// 开始调用DownloadStringAsync异步下载文档并且读取它
Appclient.DownloadStringAsync( new Uri( " http://localhost:3993/ClientBin/222.xml " , UriKind.RelativeOrAbsolute));
Appclient.DownloadStringCompleted += new DownloadStringCompletedEventHandler(Appclient_DownloadStringCompleted);
}
void Appclient_DownloadStringCompleted( object sender, DownloadStringCompletedEventArgs e)
{
MessageBox.Show(e.Result);
Appclient.DownloadStringCompleted -= new DownloadStringCompletedEventHandler(Appclient_DownloadStringCompleted);
}
#endregion
•上传Stream操作如下：
建立一个AddFileHandle.ashx,向这个文件内部写入以下代码以接收Silverlight中上传的Stream数据流。
/// <summary>
/// AddFileHandle 的摘要说明
/// </summary>
public class AddFileHandle : IHttpHandler
{
public void ProcessRequest(HttpContext context)
{
// 获取上传的数据流
using (Stream sr = context.Request.InputStream)
{
string filename = " Fir " ;
byte [] buffer = new byte [ 4096 ];
int bytesRead = 0 ;
// 将当前数据流写入ClientBin文件下Fir.jpg文件中
using (FileStream fs = File.Create(context.Server.MapPath( " ClientBin/ " + filename + " .jpg " ), 4096 ))
{
while ((bytesRead = sr.Read(buffer, 0 , buffer.Length)) > 0 )
{
// 将数据写入文件
fs.Write(buffer, 0 , bytesRead);
}
}
}
}
public bool IsReusable
{
get
{
return false ;
}
}
}
Silverlight读取图片数据，然后传到服务器端（注：此处没有验证传什么数据，如有需要自己调用OpenFileDialog.Filter即可），代码如下：
#region OpenWriteAsync上传图片
private void buttonOpenWriteAsync_Click( object sender, RoutedEventArgs e)
{
OpenFileDialog dialog = new OpenFileDialog();
if (dialog.ShowDialog() == true )
{
// 开始调用OpenWriteAsync方法上传数据
Appclient.OpenWriteAsync( new Uri( " http://localhost:3993/AddFileHandle.ashx " , UriKind.RelativeOrAbsolute), " POST " , dialog.File.OpenRead());
Appclient.OpenWriteCompleted += new OpenWriteCompletedEventHandler(Appclient_OpenWriteCompleted);
}
}
void Appclient_OpenWriteCompleted( object sender, OpenWriteCompletedEventArgs e)
{
// 将图片数据流发送到服务器上
Stream inputStream = e.UserState as Stream;
Stream outputStream = e.Result;
byte [] buffer = new byte [ 4096 ];
int bytesRead = 0 ;
while ((bytesRead = inputStream.Read(buffer, 0 , buffer.Length)) > 0 )
{
outputStream.Write(buffer, 0 , bytesRead);
}
outputStream.Close();
inputStream.Close();
MessageBox.Show( " 图片上传成功！ " );
Appclient.OpenWriteCompleted -= new OpenWriteCompletedEventHandler(Appclient_OpenWriteCompleted);
}
#endregion
•下载Stream操作如下：
本例采用上一节的源码，下载Stream流，然后反射为对象，源码如下：
#region OpenReadAsync下载XAP
private void buttonOpenReadAsync_Click( object sender, RoutedEventArgs e)
{
// 1 •使用WebClient下载SLRandarHitTest.xap文件，进行异步读取。
Appclient.OpenReadAsync( new Uri( " SLRandarHitTest.xap " , UriKind.Relative));
Appclient.OpenReadCompleted += new OpenReadCompletedEventHandler(Appclient_OpenReadCompleted);
}
void Appclient_OpenReadCompleted( object sender, OpenReadCompletedEventArgs e)
{
CreateXAPResource( " SLRandar.dll " , " SLRandar.MainPage " , e.Result);
Appclient.OpenReadCompleted -= new OpenReadCompletedEventHandler(Appclient_OpenReadCompleted);
}
/// <summary>
/// 创建XAP包的反射实例并且加装到Canvas中
/// </summary>
/// <param name="dllStr"> XAP包中的编译完成的运行代码的DLL文件 </param>
/// <param name="mainStr"> 需要实例化的启动页面 </param>
/// <param name="resultStream"> 使用WebClient下载到的数据流 </param>
private void CreateXAPResource( string dllStr, string mainStr, Stream resultStream)
{
// 3 •获取其他包提供的资源流信息
StreamResourceInfo streamResourceInfo = Application.GetResourceStream( new StreamResourceInfo(resultStream as Stream, null ), new Uri(dllStr, UriKind.RelativeOrAbsolute));
// 4 •对Stream进行反射
AssemblyPart assemblyPart = new AssemblyPart();
Assembly assembly = assemblyPart.Load(streamResourceInfo.Stream);
// 5 •(创建实例
var uc = (UserControl)assembly.CreateInstance(mainStr);
lRoot.Children.Clear();
lRoot.Children.Add(uc);
}
#endregion
