Silverlight的RIA应用中访问远端的WebService或WCF服务，都是通过异步线程模式调用的。在某些情况下我们的调用是需要同步进行，虽然Silverlight没有内置同步线程模式调用远端服务接口，但是我们可以通过多线程的处理来伪装出同步调用的实现。在.NET Framework的多线程编程中提供了丰富的线程接口，其中AutoResetEvent和ManualResetEvent在多线程编码中最为常用，本文将介绍如何通过AutoResetEvent的线程等待特性实现Silverlight同步调用远端WCF服务。
一、定义WCF服务
为了演示同步调用WCF服务的实现，提供一个简单的WCF服务接口，完成返回一本图书基本信息，WCF服务接口定义如下：
[ServiceContract]
public interface IDataService
{
[OperationContract]
Book GetBook();
}
public class Book
{
public int ID { get ; set ; }
public string Name { get ; set ; }
public string Author { get ; set ; }
public double Price { get ; set ; }
}
public interface IDataService
{
[OperationContract]
Book GetBook();
}
public class Book
{
public int ID { get ; set ; }
public string Name { get ; set ; }
public string Author { get ; set ; }
public double Price { get ; set ; }
}
接口提供一个返回图书基本信息的方法，包括图书编好，图书名，图书作者以及图书价格。接口具体的实现如下代码：
public
class
DataService : IDataService
{
public Book GetBook()
{
return new Book
{
ID = 1001 ,
Name = " 《三国演义》 " ,
Author = " 罗贯中 " ,
Price = 89.50
};
}
}
{
public Book GetBook()
{
return new Book
{
ID = 1001 ,
Name = " 《三国演义》 " ,
Author = " 罗贯中 " ,
Price = 89.50
};
}
}
如上提供可正常运行的WCF服务接口，在需要调用接口的地方通过WEB引用既可生成该服务的客户端代理对象。
二、基于MVVM模式的视图模型
MVVM模式的核心为INotifyPropertyChanged接口，对于实体模型对象和UI控件元素间提供了完善的同步更新特性。为了方便界面元素同步更新，这里引入了MVVP模式的简单应用。
public
class
ViewModelBase : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
protected void RaisePropertyChangedEvent( string propertyName)
{
var handler = PropertyChanged;
if (handler != null )
handler( this , new PropertyChangedEventArgs(propertyName));
}
}
{
public event PropertyChangedEventHandler PropertyChanged;
protected void RaisePropertyChangedEvent( string propertyName)
{
var handler = PropertyChanged;
if (handler != null )
handler( this , new PropertyChangedEventArgs(propertyName));
}
}
还需要对应于服务接口中的Book对象定义一个ViewModel对象，详细如下代码所示：
public
class
BookViewModel : ViewModelBase
{
private int iD;
/// <summary>
/// 图书ID
/// </summary>
public int ID
{
get { return iD; }
set
{
iD = value;
RaisePropertyChangedEvent( " ID " );
}
}
private string name;
/// <summary>
/// 图书名称
/// </summary>
public string Name
{
get { return name; }
set
{
name = value;
RaisePropertyChangedEvent( " Name " );
}
}
private string author;
/// <summary>
/// 图书作者
/// </summary>
public string Author
{
get { return author; }
set
{
author = value;
RaisePropertyChangedEvent( " Author " );
}
}
private double price;
/// <summary>
/// 图书价格
/// </summary>
public double Price
{
get { return price; }
set
{
price = value;
RaisePropertyChangedEvent( " Price " );
}
}
}
{
private int iD;
/// <summary>
/// 图书ID
/// </summary>
public int ID
{
get { return iD; }
set
{
iD = value;
RaisePropertyChangedEvent( " ID " );
}
}
private string name;
/// <summary>
/// 图书名称
/// </summary>
public string Name
{
get { return name; }
set
{
name = value;
RaisePropertyChangedEvent( " Name " );
}
}
private string author;
/// <summary>
/// 图书作者
/// </summary>
public string Author
{
get { return author; }
set
{
author = value;
RaisePropertyChangedEvent( " Author " );
}
}
private double price;
/// <summary>
/// 图书价格
/// </summary>
public double Price
{
get { return price; }
set
{
price = value;
RaisePropertyChangedEvent( " Price " );
}
}
}
三、基于AutoResetEvent的同步实现
利用AutoResetEvent的线程等待特性，可以折中实现Silverlight同步调用远端WCF服务。其原理就是在Silverlight发起异步调用远端WCF的时候进行线程阻塞，比记录异步调用远端WCF服务接口的完成事件，当异步调用完成后就终止线程阻塞，从而获取状态事件对象中或得调用远程接口所返回的结果。由于视图模型对象实现了INotifyPropertyChanged接口能够及时的更新界面元素，以此间接的就实现了同步方式调用。
public
class
AsyncCallStatus
<
T
>
{
public AsyncCallStatus()
{
}
public T CompletedEventArgs { get ; set ; }
}
{
public AsyncCallStatus()
{
}
public T CompletedEventArgs { get ; set ; }
}
public
class
BookFacade
{
private AutoResetEvent autoResetEvent = new AutoResetEvent( false );
public void GetBook(BookViewModel viewModel)
{
if (viewModel == null )
{
throw new ArgumentNullException( " viewModel " , " 参数不能为空。 " );
}
DataService.DataServiceClient client = new DataService.DataServiceClient();
client.GetBookCompleted += client_GetBookCompleted;
var status = new AsyncCallStatus < GetBookCompletedEventArgs > ();
client.GetBookAsync(status);
// 阻塞线程
autoResetEvent.WaitOne();
if (status.CompletedEventArgs.Error != null )
{
throw status.CompletedEventArgs.Error;
}
var book = status.CompletedEventArgs.Result;
viewModel.ID = book.ID;
viewModel.Name = book.Name;
viewModel.Author = book.Author;
viewModel.Price = book.Price;
}
private void client_GetBookCompleted( object sender, GetBookCompletedEventArgs e)
{
var status = e.UserState as AsyncCallStatus < GetBookCompletedEventArgs > ;
status.CompletedEventArgs = e;
// 终止线程阻塞
autoResetEvent.Set();
}
}
{
private AutoResetEvent autoResetEvent = new AutoResetEvent( false );
public void GetBook(BookViewModel viewModel)
{
if (viewModel == null )
{
throw new ArgumentNullException( " viewModel " , " 参数不能为空。 " );
}
DataService.DataServiceClient client = new DataService.DataServiceClient();
client.GetBookCompleted += client_GetBookCompleted;
var status = new AsyncCallStatus < GetBookCompletedEventArgs > ();
client.GetBookAsync(status);
// 阻塞线程
autoResetEvent.WaitOne();
if (status.CompletedEventArgs.Error != null )
{
throw status.CompletedEventArgs.Error;
}
var book = status.CompletedEventArgs.Result;
viewModel.ID = book.ID;
viewModel.Name = book.Name;
viewModel.Author = book.Author;
viewModel.Price = book.Price;
}
private void client_GetBookCompleted( object sender, GetBookCompletedEventArgs e)
{
var status = e.UserState as AsyncCallStatus < GetBookCompletedEventArgs > ;
status.CompletedEventArgs = e;
// 终止线程阻塞
autoResetEvent.Set();
}
}
四、Silverlight前端调用
Siverlight前端就简单布局一个表单作为数据呈现界面，其代码如下：
<
Grid
x:Name
="LayoutRoot"
Background
="White"
>
< Grid HorizontalAlignment ="Left" Name ="grid1" VerticalAlignment ="Top" Width ="300" Margin ="20" >
< Grid.RowDefinitions >
< RowDefinition Height ="30" ></ RowDefinition >
< RowDefinition Height ="30" ></ RowDefinition >
< RowDefinition Height ="30" ></ RowDefinition >
< RowDefinition Height ="30" ></ RowDefinition >
< RowDefinition Height ="30" ></ RowDefinition >
</ Grid.RowDefinitions >
< Grid.ColumnDefinitions >
< ColumnDefinition Width ="60" ></ ColumnDefinition >
< ColumnDefinition Width ="*" ></ ColumnDefinition >
</ Grid.ColumnDefinitions >
< sdk:Label HorizontalAlignment ="Left" Content ="图书编号：" VerticalAlignment ="Center" Grid.Column ="0" Grid.Row ="0" />
< TextBox Text =" {Binding ID} " Grid.Column ="1" Grid.Row ="0" ></ TextBox >
< sdk:Label HorizontalAlignment ="Left" Content ="图书名称：" VerticalAlignment ="Center" Grid.Column ="0" Grid.Row ="1" />
< TextBox Text =" {Binding Name} " Grid.Column ="1" Grid.Row ="1" ></ TextBox >
< sdk:Label HorizontalAlignment ="Left" Content ="图书作者：" VerticalAlignment ="Center" Grid.Column ="0" Grid.Row ="2" />
< TextBox Text =" {Binding Author} " Grid.Column ="1" Grid.Row ="2" ></ TextBox >
< sdk:Label HorizontalAlignment ="Left" Content ="图书价格：" VerticalAlignment ="Center" Grid.Column ="0" Grid.Row ="3" />
< TextBox Text =" {Binding Price} " Grid.Column ="1" Grid.Row ="3" ></ TextBox >
< Button Content ="查询" Grid.Column ="1" Grid.Row ="4" Width ="60" Height ="23" Click ="Button_Click" ></ Button >
</ Grid >
</ Grid >
< Grid HorizontalAlignment ="Left" Name ="grid1" VerticalAlignment ="Top" Width ="300" Margin ="20" >
< Grid.RowDefinitions >
< RowDefinition Height ="30" ></ RowDefinition >
< RowDefinition Height ="30" ></ RowDefinition >
< RowDefinition Height ="30" ></ RowDefinition >
< RowDefinition Height ="30" ></ RowDefinition >
< RowDefinition Height ="30" ></ RowDefinition >
</ Grid.RowDefinitions >
< Grid.ColumnDefinitions >
< ColumnDefinition Width ="60" ></ ColumnDefinition >
< ColumnDefinition Width ="*" ></ ColumnDefinition >
</ Grid.ColumnDefinitions >
< sdk:Label HorizontalAlignment ="Left" Content ="图书编号：" VerticalAlignment ="Center" Grid.Column ="0" Grid.Row ="0" />
< TextBox Text =" {Binding ID} " Grid.Column ="1" Grid.Row ="0" ></ TextBox >
< sdk:Label HorizontalAlignment ="Left" Content ="图书名称：" VerticalAlignment ="Center" Grid.Column ="0" Grid.Row ="1" />
< TextBox Text =" {Binding Name} " Grid.Column ="1" Grid.Row ="1" ></ TextBox >
< sdk:Label HorizontalAlignment ="Left" Content ="图书作者：" VerticalAlignment ="Center" Grid.Column ="0" Grid.Row ="2" />
< TextBox Text =" {Binding Author} " Grid.Column ="1" Grid.Row ="2" ></ TextBox >
< sdk:Label HorizontalAlignment ="Left" Content ="图书价格：" VerticalAlignment ="Center" Grid.Column ="0" Grid.Row ="3" />
< TextBox Text =" {Binding Price} " Grid.Column ="1" Grid.Row ="3" ></ TextBox >
< Button Content ="查询" Grid.Column ="1" Grid.Row ="4" Width ="60" Height ="23" Click ="Button_Click" ></ Button >
</ Grid >
</ Grid >
通过按钮执行调用WCF服务接口查询图书信息，按钮事件直接使用上面所写的图书门面类（BookFacade）的调用服务方法即可。
private
void
Button_Click(
object
sender, RoutedEventArgs e)
{
try
{
ThreadPool.QueueUserWorkItem( delegate ( object o)
{
BookViewModel viewModel = new BookViewModel();
new BookFacade().GetBook(viewModel);
Deployment.Current.Dispatcher.BeginInvoke(() => this .DataContext = viewModel);
});
}
catch (Exception ex)
{
MessageBox.Show(ex.ToString());
}
}
{
try
{
ThreadPool.QueueUserWorkItem( delegate ( object o)
{
BookViewModel viewModel = new BookViewModel();
new BookFacade().GetBook(viewModel);
Deployment.Current.Dispatcher.BeginInvoke(() => this .DataContext = viewModel);
});
}
catch (Exception ex)
{
MessageBox.Show(ex.ToString());
}
}
最终的运行如下图所示效果：
