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：
结束语本文简单介绍了Silverlight 2中使用Web Client进行通信的知识，在Silverlight 2中，提供的通信API非常丰富，后面将会介绍其他的方式。你可以从
这里下载本文示例代码。
