silverlight 4数据与通信之WebRequest详解

此篇博文基于《silverlight4数据与通信之WebClient详解 silverlight4版》，查看请请点击这里

这里用上一篇文章用过的示例，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。

        <TextBlock x:Name="lblPrice" Text="价格：" Foreground="White" 
                   HorizontalAlignment="Left" VerticalAlignment="Center" 
                   Margin="20 0 0 0"></TextBlock> 
    </Border> 
</Grid>    <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"> <Grid Background="#46461F"> 

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： 

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;

namespace sample.Web
{
    /// <summary>
    /// BookHandler2 的摘要说明
    /// </summary>
    public class BookHandler2 : 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

private void UserControl_Loaded(object sender, RoutedEventArgs e)
        {
            List<BookClass> books = new List<BookClass>() 
            {  
                new BookClass("Professional ASP.NET 3.5"), 
                new BookClass("ASP.NET AJAX In Action"), 
                new BookClass("Silverlight In Action"), 
                new BookClass("ASP.NET 3.5 Unleashed"), 
                new BookClass("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;

        private void Books_SelectionChanged(object sender, SelectionChangedEventArgs e)
        {
            bookNo = Books.SelectedIndex.ToString();
            //端口可根据自己的情况随便更改
            Uri endpoint = new Uri(String.Format("http://localhost:80/BookHandler2.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。要注意添加System.IO命名空间。 

 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();
            }
            request.BeginGetResponse(new AsyncCallback(ResponseReady), request);
        }

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(); 

                //lblPrice.Dispatcher.BeginInvoke(new UpdatePriceDelegate(UpdatePrice), reader.ReadToEnd());

                //‘charleslau’的方法，可以运行
                string price = reader.ReadToEnd();
                if (this.lblPrice.CheckAccess())
                {
                    this.lblPrice.Text = "价格:" + price;
                }
                else
                {
                    this.Dispatcher.BeginInvoke(new UIContextChangedEventHandler(UIContextChanged), price);
                } 
            }
        }
        public delegate void UIContextChangedEventHandler(object state);

        private void UIContextChanged(object state)
        {
            this.lblPrice.Text = "价格:" + (String)state;
        }

至此，大功告成，可以访问了，效果参见上一篇博文，文中有很多注释的地方，那是我参考的实例是silverlight2beta版测试通过的，在silverlight4中有些许不同，我已经做了修改，代码测试可以通过。下面附加后台完整代码

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Shapes;
using System.IO;

namespace sample
{
    public partial class s13 : UserControl
    {
        public s13()
        {
            InitializeComponent();
        }

        private void UserControl_Loaded(object sender, RoutedEventArgs e)
        {
            List<BookClass> books = new List<BookClass>() 
            {  
                new BookClass("Professional ASP.NET 3.5"), 
                new BookClass("ASP.NET AJAX In Action"), 
                new BookClass("Silverlight In Action"), 
                new BookClass("ASP.NET 3.5 Unleashed"), 
                new BookClass("Introducing Microsoft ASP.NET AJAX") 
            };

            Books.ItemsSource = books;
        }
        private string bookNo;

        private void Books_SelectionChanged(object sender, SelectionChangedEventArgs e)
        {
            bookNo = Books.SelectedIndex.ToString();
            //端口可根据自己的情况随便更改
            Uri endpoint = new Uri(String.Format("http://localhost:80/BookHandler2.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); 
        }

        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();
            }
            request.BeginGetResponse(new AsyncCallback(ResponseReady), request);
        }

        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(); 

                //lblPrice.Dispatcher.BeginInvoke(new UpdatePriceDelegate(UpdatePrice), reader.ReadToEnd());

                //‘charleslau’的方法，可以运行
                string price = reader.ReadToEnd();
                if (this.lblPrice.CheckAccess())
                {
                    this.lblPrice.Text = "价格:" + price;
                }
                else
                {
                    this.Dispatcher.BeginInvoke(new UIContextChangedEventHandler(UIContextChanged), price);
                } 
            }
        }
        public delegate void UIContextChangedEventHandler(object state);

        private void UIContextChanged(object state)
        {
            this.lblPrice.Text = "价格:" + (String)state;
        }


        //private void UpdatePrice(string price)
        //{
        //    lblPrice.Text = "price:" + price;
        //}
        //private delegate void UpdatePriceDelegate(string price);
    }
}

参考资料：http://www.cnblogs.com/Terrylee/archive/2008/03/09/silverlight2-step-by-step-part13-data-and-communication-webrequest.html

感谢李老师和回帖的前辈，我对数据通信知之甚少，如有纰漏，敬请指出