一步一步学Silverlight 2系列（13）：数据与通信之WebRequest

时间: 2008-03-09 18:13

概述Silverlight 2 Beta 1版本发布了，无论从Runtime还是Tools都给我们带来了很多的惊喜，如支持框架语言Visual Basic, Visual C#, IronRuby, Ironpython，对JSON、Web Service、WCF以及Sockets的支持等一系列新的特性。《一步一步学Silverlight 2系列》文章带您快速进入Silverlight 2开发。
本文将简单介绍在Silverlight 2中如何使用WebRequest进行数据的提交和获取。
简单示例在本文中，我们仍然使用在一步一步学Silverlight 2系列（12）：数据与通信之WebClient中用过的示例，只不过稍微做一点小的改动，使用WebRequest提交书籍编号数据，并根据书籍号返回价格信息。最终运行的结果如下图：

编写界面布局，XAML如下：
<Grid Background="#46461F">
<Grid.RowDefinitions>
<RowDefinition Height="40">
</RowDefinition>
<RowDefinition Height="*">
</RowDefinition>
<RowDefinition Height="40">
</RowDefinition>
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition>
</ColumnDefinition>
</Grid.ColumnDefinitions>
<Border Grid.Row="0" Grid.Column="0" CornerRadius="15" Width="240" Height="36" Margin="20 0 0 0" HorizontalAlignment="Left">
<TextBlock Text="书籍列表" Foreground="White" HorizontalAlignment="Left" VerticalAlignment="Center" Margin="20 0 0 0">
</TextBlock>
</Border>
<ListBox x:Name="Books" Grid.Row="1" Margin="40 10 10 10" SelectionChanged="Books_SelectionChanged">
<ListBox.ItemTemplate>
<DataTemplate>
<StackPanel>
<TextBlock Text="{Binding Name}" Height="32"></TextBlock>
</StackPanel>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
<Border Grid.Row="2" Grid.Column="0" CornerRadius="15" Width="240" Height="36" Background="Orange" Margin="20 0 0 0" HorizontalAlignment="Left">
<TextBlock x:Name="lblPrice" Text="价格：" Foreground="White" HorizontalAlignment="Left" VerticalAlignment="Center" Margin="20 0 0 0">
</TextBlock>
</Border>
</Grid>
编写HttpHandler，注意我使用了context.Request.Form["No"]，在后面我们将使用WebRequest在RequestReady方法中将数据写入请求流：

public class BookHandler : IHttpHandler
{
public static readonly string[] PriceList = new string[]{ "66.00","78.30","56.50", "28.80","77.00"};
public void ProcessRequest(HttpContext context)
{

context.Response.ContentType = "text/plain";
context.Response.Write(PriceList[Int32.Parse(context.Request.Form["No"])]);
}
public bool IsReusable
{
get
{
return false;
}
}

}

在界面加载时绑定书籍列表，关于数据绑定可以参考一步一步学Silverlight 2系列（11）：数据绑定。

private void UserControl_Loaded(object sender, RoutedEventArgs e)
{

List<Book> books = new List<Book>()
{
new Book("Professional ASP.NET 3.5"),new Book("ASP.NET AJAX In Action"),new Book("Silverlight In Action"),new Book("ASP.NET 3.5 Unleashed"),new Book("Introducing Microsoft ASP.NET AJAX")
};
Books.ItemsSource = books;

}

接下来在SelectionChanged事件中实现用户选择书籍时，我们使用WebRequest提交书籍编号，并且获得价格数据，仍然采用异步模式，提供RequestReady和ResponseReady两个回调函数：

private string bookNo;void Books_SelectionChanged(object sender, SelectionChangedEventArgs e)
{

bookNo = Books.SelectedIndex.ToString();
Uri endpoint = new Uri(http://localhost:49955/BookHandler.ashx);
WebRequest request = WebRequest.Create(endpoint);
request.Method = "POST";
request.ContentType = "application/x-www-form-urlencoded";
request.BeginGetRequestStream(new AsyncCallback(RequestReady), request); request.BeginGetResponse(new AsyncCallback(ResponseReady), request);

}

实现RequestReady方法，将书籍的编号写入请求流中。

void RequestReady(IAsyncResult asyncResult)
{

WebRequest request = asyncResult.AsyncState as WebRequest;
Stream requestStream = request.EndGetRequestStream(asyncResult);
using (StreamWriter writer = new StreamWriter(requestStream))
{
writer.Write(String.Format("No={0}", bookNo));
writer.Flush();
}

}

实现ResponseReady方法，显示返回的结果。

void ResponseReady(IAsyncResult asyncResult)
{

WebRequest request = asyncResult.AsyncState as WebRequest;
WebResponse response = request.EndGetResponse(asyncResult);
using (Stream responseStream = response.GetResponseStream())
{
StreamReader reader = new StreamReader(responseStream);
lblPrice.Text = "价格：" + reader.ReadToEnd();
}