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

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。@H_502_9@

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。@H_502_9@

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：@H_502_9@

编写界面布局，XAML如下：@H_502_9@

<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"
            @H_835_32@margin="20 0 0 0" HorizontalAlignment="Left">
        <TextBlock Text="书籍列表" Foreground="White"
                   HorizontalAlignment="Left" VerticalAlignment="Center"
                   @H_835_32@margin="20 0 0 0"></TextBlock>
    </Border>
    <ListBox x:Name="Books" Grid.Row="1" @H_835_32@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"
            @H_835_32@margin="20 0 0 0" HorizontalAlignment="Left">
        <TextBlock x:Name="lblPrice" Text="价格：" Foreground="White"
                   HorizontalAlignment="Left" VerticalAlignment="Center"
                   @H_835_32@margin="20 0 0 0"></TextBlock>
    </Border>
</Grid>

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。@H_502_9@

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：@H_502_9@

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。@H_502_9@

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。@H_502_9@

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：@H_502_9@

用户选择一本书籍后，将显示其价格：@H_502_9@

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。@H_502_9@

下一篇：一步一步学Silverlight 2系列（14）：数据与通信之WCF@H_502_9@