第13课 数据与通信之WebRequest

概述

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)
{
    ListBook> books = new ListBook>() { 
        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();
    }
}

最后运行的结果如下：

用户选择一本书籍后，将显示其价格：

结束语

本文简单介绍了在Silverlight 2中如何使用WebRequest提交和获取数据，你可以从这里下载示例程序。