一步一步学Silverlight 2系列（12）：数据与通信之WebClient

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。
本文将介绍如何在Silverlight 2中使用Web Client进行通信。
简单示例编写一个简单的示例，在该示例中，选择一本书籍之后，我们通过Web Client去查询书籍的价格，并显示出来，最终的效果如下：

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>
为了模拟查询价格，我们编写一个HttpHandler，接收书籍的No，并返回价格：
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.QueryString["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。
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;
}
接下来当用户选择一本书籍时，需要通过Web Client去获取书籍的价格，在Silverlight 2中，所有的网络通信API都设计为了异步模式。在声明一个Web Client实例后，我们需要为它注册DownloadStringCompleted事件处理方法，在下载完成后将会被回调，然后再调用DownloadStringAsync方法开始下载。
void Books_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
Uri endpoint = new Uri(String.Format("http://localhost:49955/BookHandler.ashx?No={0}",Books.SelectedIndex));
WebClient client = new WebClient();
client.DownloadStringCompleted += new
DownloadStringCompletedEventHandler(client_DownloadStringCompleted);
client.DownloadStringAsync(endpoint);}void client_DownloadStringCompleted(object sender,
DownloadStringCompletedEventArgs e){
if (e.Error == null)
{
lblPrice.Text = "价格：" + e.Result;
}
else
{
lblPrice.Text = e.Error.Message;
}
}
注意大家可以在Web Application Project的属性页中，把ASP.NET Development Server的端口号设置为一个固定的端口号：

最后完整的代码如下：
public partial class Page : UserControl
{
public Page()
{
InitializeComponent();
}
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;
}
void Books_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
Uri endpoint = new Uri(String.Format("http://localhost:49955/BookHandler.ashx?No={0}",Books.SelectedIndex));
WebClient client = new WebClient();
client.DownloadStringCompleted += new
DownloadStringCompletedEventHandler(client_DownloadStringCompleted);
client.DownloadStringAsync(endpoint);
}
void client_DownloadStringCompleted(object sender, DownloadStringCompletedEventArgs e)
{
if (e.Error == null)
{
lblPrice.Text = "价格：" + e.Result;
}
else
{
lblPrice.Text = e.Error.Message;
}
}
}
运行后效果如下：

当我们选择其中一本书籍时，将会显示出它的价格：