Silverlight的RIA應(yīng)用中訪問遠(yuǎn)端的WebService或WCF服務(wù)，都是通過異步線程模式調(diào)用的。在某些情況下我們的調(diào)用是需要同步進(jìn)行，雖然Silverlight沒有內(nèi)置同步線程模式調(diào)用遠(yuǎn)端服務(wù)接口，但是我們可以通過多線程的處理來偽裝出同步調(diào)用的實(shí)現(xiàn)。在.NET Framework的多線程編程中提供了豐富的線程接口，其中AutoResetEvent和ManualResetEvent在多線程編碼中最為常用，本文將介紹如何通過AutoResetEvent的線程等待特性實(shí)現(xiàn)Silverlight同步調(diào)用遠(yuǎn)端WCF服務(wù)。

　　一、定義WCF服務(wù)

　　為了演示同步調(diào)用WCF服務(wù)的實(shí)現(xiàn)，提供一個(gè)簡單的WCF服務(wù)接口，完成返回一本圖書基本信息，WCF服務(wù)接口定義如下：

[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;?}
}

　　接口提供一個(gè)返回圖書基本信息的方法，包括圖書編好，圖書名，圖書作者以及圖書價(jià)格。接口具體的實(shí)現(xiàn)如下代碼：

public?class?DataService?:?IDataService
{
????public?Book?GetBook()
????{
????????return?new?Book
????????{
????????????ID?=?1001,
????????????Name?=?"《三國演義》",
????????????Author?=?"羅貫中",
????????????Price?=?89.50
????????};
????}
}

?　　如上提供可正常運(yùn)行的WCF服務(wù)接口，在需要調(diào)用接口的地方通過WEB引用既可生成該服務(wù)的客戶端代理對象。

　　二、基于MVVM模式的視圖模型

　　MVVM模式的核心為INotifyPropertyChanged接口，對于實(shí)體模型對象和UI控件元素間提供了完善的同步更新特性。為了方便界面元素同步更新，這里引入了MVVP模式的簡單應(yīng)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上海企業(yè)網(wǎng)站設(shè)計(jì)與制作));
????}
}

　　還需要對應(yīng)于服務(wù)接口中的Book對象定義一個(gè)ViewModel對象，詳細(xì)如下代碼所示：

public?class?BookViewModel?:?ViewModelBase
{
????privateint?iD;
????///?<summary>
????///?圖書ID
????///?</summary>
????public?int?ID
????{
????????get?{?return?iD;?}
????????set
????????{
????????????iD?=?value;
????????????RaisePropertyChangedEvent("ID");
????????}
????}

????private?string?name;
????///?<summary>
????///?圖書名稱
????///?</summary>
????public?string?Name
????{
????????get?{?return?name;?}
????????set
????????{
????????????name?=?value;
????????????RaisePropertyChangedEvent("Name");
????????}
????}

????private?string?author;
????///?<summary>
????///?圖書作者
????///?</summary>
????上海閔行企業(yè)網(wǎng)站設(shè)計(jì)與制作tyle="color: #0000ff;">public?string?Author
????{
????????get?{?return?author;?}
????????set
????????{
????????????author?=?value;
????????????RaisePropertyChangedEvent("Author");
????????}
????}

????private?double?price;
????///?<summary>
????///?圖書價(jià)格
????///?</summary>
????public?double?Price
????{
????????get?{?return?price;?}
????????set
????????{
????????????price?=?value;
????????????RaisePropertyChangedEvent("Price");
????????}
????}
}

三、基于AutoResetEvent的同步實(shí)現(xiàn)

?　　利用AutoResetEvent的線程等待特性，可以折中實(shí)現(xiàn)Silverlight同步調(diào)用遠(yuǎn)端WCF服務(wù)。其原理就是在Silverlight發(fā)起異步調(diào)用遠(yuǎn)端WCF的時(shí)候進(jìn)行線程阻塞，比記錄異步調(diào)用遠(yuǎn)端WCF服務(wù)接口的完成事件，當(dāng)異步調(diào)用完成后就終止線程阻塞，從而獲取狀態(tài)事件對象中或得調(diào)用遠(yuǎn)程接口所返回的結(jié)果。由于視圖模型對象實(shí)現(xiàn)了INotifyPropertyChanged接口能夠及時(shí)的更新界面元素，以此間接的就實(shí)現(xiàn)了同步方式調(diào)用。

public?class?AsyncCallStatus<T>
{
????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",?"參數(shù)不能為空。");
????????}

????????DataService.DataServiceClient?client?=?new?DataService.DataServiceClient();
????????client.GetBookCompleted?+=?client_GetBookCompleted;

????????var?status?=?new?AsyncCallStatus<GetBookCompletedEventArgs>();
????????client.GetBookAsync(status);
????????//阻塞線程
????????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;
????????//終止線程阻塞
????????autoResetEvent.Set();
????}
}

　　四、Silverlight前端調(diào)用

　　Siverlight前端就簡單布局一個(gè)表單作為數(shù)據(jù)呈現(xiàn)界面，其代碼如下：

<Grid?x:Name="LayoutRoot"?Background="White">
????<Grid?HorizontalAlignment="Left"?Name="grid1"?VerticalAlignment="Top"?Width="300"?Margin="20">
????????<Grid.RowDefinitions>
????????????<RowDefinition?Height="30"上海網(wǎng)站建設(shè)pan>></RowDefinition>
????????????<RowDefinition?Height="30"></RowDefinition>
????????????<RowDefinition?Height="30"></RowDefinition>
????????????<RowDefinition?Height="30"></RowDefinition>
????????????<R上海企業(yè)網(wǎng)站制作owDefinition?Height="30"></RowDefinition>
????????</Grid.RowDefinitions>
????????<Grid.ColumnDefinitions>
????????????<ColumnDefinition?Width="60"></ColumnDefinition>
????????????<ColumnDefinition?Width="*"></ColumnDefinition>
????????</Grid.ColumnDefinitions>
????????<sdk:Label??HorizontalAlignment="Left"?Content="圖書編號："?VerticalAlignment="Center"?Grid.Column="0"?Grid.Row="0"/>
????????<TextBox?Text="{Binding?ID}"?Grid.Column="1"?Grid.Row="0"></TextBox>
????????<sdk:Label??HorizontalAlignment="Left"?Content="圖書名稱："?VerticalAlignment="Center"?Grid.Column="0"?Grid.Row="1"/>
????????<TextBox?Text="{Binding?Name}"?Grid.Column="1"?Grid.Row="1"></TextBox>
????????<sdk:Label??HorizontalAlignment="Left"?Content="圖書作者："?VerticalAlignment="Center"?Grid.Column="0"?Grid.Row="2"/>
????????<TextBox?Text="{Binding?Author}"?Grid.Column="1"?Grid.Row="2"></TextBox>
????????<sdk:Label??HorizontalAlignment="Left"?Content="圖書價(jià)格："?VerticalAlignment="Center"?Grid.Column="0"?Grid.Row="3"/>
????????<TextBox?Text="上海徐匯企業(yè)網(wǎng)站制作le="color: #808000;">{Binding?Price}"?Grid.Column="1"?Grid.Row="3"></TextBox>?
????????????
????????<Button?Content="查詢"?Grid.Column="1"?Grid.Row="4"?Width="60"?Height="23"?Click="Button_Click"></Button>
????</Grid>
</Grid>

?　　通過按鈕執(zhí)行調(diào)用WCF服務(wù)接口查詢圖書信息，按鈕事件直接使用上面所寫的圖書門面類（BookFacade）的調(diào)用服務(wù)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());
????}
}

?　　最終的運(yùn)行如下圖所示效果：

　　

　　

轉(zhuǎn)載于:https://www.cnblogs.com/waw/archive/2011/10/18/2216979.html

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