使用MEF构建可扩展的Silverlight应用

“托管扩展性框架(Managed Extensibility Framework,简称MEF),是微软 .NET框架下为提高应用和组件复用程度而推出的,用于使组件能够最大化的重用 。使用MEF能够使静态编译的.NET应用程序转换为动态组合,这将是创建可扩展应 用、可扩展框架和应用扩展的好途径。它将做为.NET Framework 4.0的组成部分 之一发布。现在,MEF也将被包含在Silverlight 4.0中。

那么MEF是怎样工作的呢?简单分为三个步骤:

Export (输出)

Import (输入)

Compose (组合)

简短说一下MEF的工作原理,MEF的核心包括一个catalog和一个 CompositionContainer。category用于发现扩展,而container用于协调创建和梳 理依赖性。每个可组合的Part提供了一个或多个Export,并且通常依赖于一个或 多个外部提供的服务或 Import。每个Part管理一个实例为应用程序运行。

下面我们做一个小型可扩展计算器示例来解释这三个过程

1.首先下载MEF框架包,Silverlight 4.0会自带,不过微软已经将其开源了。

http://www.codeplex.com/MEF

2.创建一个Silverlight Navigate Application ,并添加程序集引用 (MEF_Beta_2\bin\SL目录下 System.ComponentModel.Composition.dll)

在项目下添加两个类文件Package.cs和PackageCatalog.cs,这两个文件在最 新的MEF版本中没有提供,主要用于加载silverlight的Xap包。

这两个文件在MEF框架的Sample中提供了(MEF_Beta_2 \Samples\PictureViewer\PictureViewer.Common),将这两个类的访问修饰符改 为public, 添加后注意修改命名空间。

3.修改Home.cs 类

代码

using System;
       using System.Net;
       using System.Windows;
       using System.Windows.Controls;
       using System.Windows.Documents;
       using System.Windows.Ink;
       using System.Windows.Input;
       using System.Windows.Media;
       using System.Windows.Media.Animation;
       using System.Windows.Shapes;
       using System.ComponentModel.Composition;
       using System.ComponentModel;
       namespace MefDemo
       {
           //用于更新界面的委托
           public delegate void OperateHandler(IOperate  Op);
           /// <summary>
           /// 运算器接口
           /// </summary>
           public interface IOperate
           {
               double Op(double left, double  right);
               string Symbol { set; get; }
               string Label { get; set; }
           }
           /// <summary>
           /// 加法运算器
           /// </summary>
           [Export(typeof(IOperate))]
           public class AddButton : Button,  IOperate
           {
               [Import ("AddButtonContract",AllowRecomposition = true)]
               public string Label { get { return  this.Content.ToString(); } set { this.Content = value; } } 
               [Import("AddSybomContract",  AllowRecomposition = true)]
               public string Symbol { set; get;  }
               [Import("ClickHandler")]
               public OperateHandler ClickAction {  get; set; }
               #region IOperate 成员
               public double Op(double left, double  right)
               {
                   return left + right;
               }
               #endregion
               public AddButton()
               {
                   this.Click += (s, e) =>  ClickAction(this);
               }
           }
           /// <summary>
           /// 减法运算器
           /// </summary>
           [Export(typeof(IOperate))]
           public class SubButton : Button,  IOperate
           {
               [Import ("SubButtonContract",AllowRecomposition=true)]
               public string Label { get { return  this.Content.ToString(); } set { this.Content = value; } } 
               [Import("SubSybomContract",  AllowRecomposition = true)]
               public string Symbol { set; get;  }
               [Import("ClickHandler")]
               public OperateHandler ClickAction {  get; set; }
               #region IOperate 成员
               public double Op(double left, double  right)
               {
                   return left - right;
               }
               #endregion
               public SubButton()
               {
                   this.Click += (s, e) =>  ClickAction(this);
               }
           }
           /// <summary>
           /// 为每个运算器的属性提供值
           /// </summary>
           public class ComponentAttributeProvider
           {
               [Export("AddButtonContract")]
               public string AddLabel  { get {  return "Add"; } }
               [Export("AddSybomContract")]
               public string AddSymbol { get {  return "+"; } }
               [Export("SubButtonContract")]
               public string SubLabel  { get {  return "Sub"; } }
               [Export("SubSybomContract")]
               public string SubSymbol { get {  return "-"; } }
           }
       }

4.修改 Home.xaml

代码

<navigation:Page x:Class="MefDemo.Home"
           xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
           xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
           xmlns:d="http://schemas.microsoft.com/expression/blend/2008"  xmlns:mc="http://schemas.openxmlformats.org/markup- compatibility/2006"
           xmlns:navigation="clr- namespace:System.Windows.Controls;assembly=System.Windows.Controls.Navi gation"
           mc:Ignorable="d" d:DesignWidth="640"  d:DesignHeight="480"
           Title="Home"
           Style="{StaticResource PageStyle}">
           <navigation:Page.Resources>
               <ItemsPanelTemplate x:Key="ItemsPanelTemplate1">
                   <StackPanel Orientation="Horizontal" HorizontalAlignment="Center"  VerticalAlignment="Center"/>
               </ItemsPanelTemplate>
           </navigation:Page.Resources>
           <Grid x:Name="LayoutRoot">
               <ScrollViewer x:Name="PageScrollViewer" Style="{StaticResource  PageScrollViewerStyle}">
                   <StackPanel x:Name="ContentStackPanel" Background="Black">
                       <StackPanel   Orientation="Horizontal" Width="455" Height="89"  Margin="91,0,91,-30">
                           <TextBox x:Name="LeftNum" HorizontalAlignment="Left"    VerticalAlignment="Center" Width="83" TextWrapping="Wrap"/>
                           <TextBlock x:Name="Symbol" Width="62" Text="+"  TextWrapping="Wrap" FontSize="24" Foreground="#FFF80606"  TextAlignment="Center" VerticalAlignment="Center"  HorizontalAlignment="Left"/>
                           <TextBox x:Name="RightNum" HorizontalAlignment="Left"    VerticalAlignment="Center" Width="78" TextWrapping="Wrap"/>
                           <TextBlock Width="64" Text="=" TextWrapping="Wrap"  Foreground="#FFF20808" FontSize="21.333" TextAlignment="Center"  VerticalAlignment="Center" HorizontalAlignment="Left"/>
                           <TextBox x:Name="Result" HorizontalAlignment="Left"    VerticalAlignment="Center" Width="146" TextWrapping="Wrap"/>
                       </StackPanel>
                       <ListBox x:Name="operateList"  ItemsSource="{Binding}"  ItemsPanel="{StaticResource ItemsPanelTemplate1}" Height="99"  Background="{x:Null}" BorderBrush="{x:Null}"/>
               <Button x:Name="DynamicLoadButton" Height="40" Width="196"  Content="DynamicLoadOperate"/>
                   </StackPanel>
               </ScrollViewer>
           </Grid>
       </navigation:Page>

5.新建类 OperatorComponent.cs

代码

using System;
       using System.Net;
       using System.Windows;
       using System.Windows.Controls;
       using System.Windows.Documents;
       using System.Windows.Ink;
       using System.Windows.Input;
       using System.Windows.Media;
       using System.Windows.Media.Animation;
       using System.Windows.Shapes;
       using System.ComponentModel.Composition;
       using System.ComponentModel;
       namespace MefDemo
       {
           //用于更新界面的委托
           public delegate void OperateHandler(IOperate  Op);
           /// <summary>
           /// 运算器接口
           /// </summary>
           public interface IOperate
           {
               double Op(double left, double  right);
               string Symbol { set; get; }
               string Label { get; set; }
           }
           /// <summary>
           /// 加法运算器
           /// </summary>
           [Export(typeof(IOperate))]
           public class AddButton : Button,  IOperate
           {
               [Import ("AddButtonContract",AllowRecomposition = true)]
               public string Label { get { return  this.Content.ToString(); } set { this.Content = value; } } 
               [Import("AddSybomContract",  AllowRecomposition = true)]
               public string Symbol { set; get;  }
               [Import("ClickHandler")]
               public OperateHandler ClickAction {  get; set; }
               #region IOperate 成员
               public double Op(double left, double  right)
               {
                   return left + right;
               }
               #endregion
               public AddButton()
               {
                   this.Click += (s, e) =>  ClickAction(this);
               }
           }
           /// <summary>
           /// 减法运算器
           /// </summary>
           [Export(typeof(IOperate))]
           public class SubButton : Button,  IOperate
           {
               [Import ("SubButtonContract",AllowRecomposition=true)]
               public string Label { get { return  this.Content.ToString(); } set { this.Content = value; } } 
               [Import("SubSybomContract",  AllowRecomposition = true)]
               public string Symbol { set; get;  }
               [Import("ClickHandler")]
               public OperateHandler ClickAction {  get; set; }
               #region IOperate 成员
               public double Op(double left, double  right)
               {
                   return left - right;
               }
               #endregion
               public SubButton()
               {
                   this.Click += (s, e) =>  ClickAction(this);
               }
           }
           /// <summary>
           /// 为每个运算器的属性提供值
           /// </summary>
           public class ComponentAttributeProvider
           {
               [Export("AddButtonContract")]
               public string AddLabel  { get {  return "Add"; } }
               [Export("AddSybomContract")]
               public string AddSymbol { get {  return "+"; } }
               [Export("SubButtonContract")]
               public string SubLabel  { get {  return "Sub"; } }
               [Export("SubSybomContract")]
               public string SubSymbol { get {  return "-"; } }
           }
       }

6.运行。 这样就构建了一个简单的运算器,其中的Export、Import就像一个 个管道一样相互连接。

# 按照这样的设计,我们想要对其进行扩展,就必须把接口分离。新建一个 Silverlight ClassLibrary Project(Named ContractLibrary),这个Library用来 封装所有的扩展接口,定义Import/Export契约。

现在把原项目中的OperatorComponent.cs 类中的接口迁移到Library项目中, 新建类文件OperateContract.cs 。

代码

using System;
using System.Net;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Ink;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Shapes;
namespace ContractLibrary
{
     public delegate void OperateHandler(IOperate Op);
     /// <summary>
     /// 运算器接口
     /// </summary>
     public interface IOperate
     {
         double Op(double left, double right);
         string Symbol { set; get; }
         string Label { get; set; }
     }
}

编译通过后在Silverlight主工程(MefDemo)中添加对ContractLibrary项目的 引用

# 再新建一个Silverlight ClassLibrary Project (Named StaticExtension),,这个工程就是我们用来静态扩展的DLL。

a).在工程下新建我们的运算器类,AddButton.cs , SubButton.cs.(代码不变 ).

b).但注意要添加对ContractLibrary项目的引用和MEF的框架集引用) 。

c).添加全局属性配置类(ComponentConfiguration.cs)

d).删除主工程中的ComponetOperater.cs.

e).添加对StaticExtension的引用.

 

OK,这样我们就可以任意扩展运算器,添加更多的扩展运算了。

那么下面是添加一个新的乘法运算所要做的工作。

在StaticExtension中添加新类 Multiply.cs

代码

using System;
using System.Net;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Ink;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Shapes;
using System.ComponentModel.Composition;
using ContractLibrary;
namespace StaticExtension
{
     /// <summary>
     /// 乘法运算器
     /// </summary>
     [Export(typeof(IOperate))]
     public class MultiplyButton : Button, IOperate
     {
         [Import("MultiplyButtonContract",  AllowRecomposition = true)]
         public string Label { get { return  this.Content.ToString(); } set { this.Content = value; } }
         [Import("MultiplySybomContract", AllowRecomposition  = true)]
         public string Symbol { set; get; }
         [Import("ClickHandler")]
         public OperateHandler ClickAction { get; set;  }
         #region IOperate 成员
         public double Op(double left, double right)
         {
             return left * right;
         }
         #endregion
         public MultiplyButton()
         {
             this.Click += (s, e) => ClickAction (this);
         }
     }
}

# 上面的是静态加载,那么现在我们使用MEF实现动态扩展运算器。桌面程序 的动态扩展是动态加载DLL,而对于Silverlight的Web程序则是动态加载Xap包了 。

新建普通Silverlight Application(Named DynamicExtension).

 

11.去掉勾选Add a test page that references the application.

1).删掉App和Main等不必要的文件,只留一个空的Silverlight项目,以减少 Xap包的大小。

2).添加ContractLibrary和MEF框架集的引用(可以将引用程序集属性 CopyLocal设置为false,因为我们在主工程中已经添加了,可以重用)

3).添加类Division.cs.

代码

using System;
       using System.Net;
       using System.Windows;
       using System.Windows.Controls;
       using System.Windows.Documents;
       using System.Windows.Ink;
       using System.Windows.Input;
       using System.Windows.Media;
       using System.Windows.Media.Animation;
       using System.Windows.Shapes;
       using System.ComponentModel.Composition;
       using ContractLibrary;
       namespace DynamicExtension
       {
           /// <summary>
           /// 乘法运算器
           /// </summary>
           [Export(typeof(IOperate))]
           public class DivisionButton : Button,  IOperate
           {
               [Import("DivisionButtonContract",  AllowRecomposition = true)]
               public string Label { get { return  this.Content.ToString(); } set { this.Content = value; } } 
               [Import("DivisionSybomContract",  AllowRecomposition = true)]
               public string Symbol { set; get;  }
               [Import("ClickHandler")]
               public OperateHandler ClickAction {  get; set; }
               #region IOperate 成员
               public double Op(double left, double  right)
               {
                   return left * right;
               }
               #endregion
               public DivisionButton()
               {
                   this.Click += (s, e) =>  ClickAction(this);
               }
           }
       }

4).添加配置类ComponentConfiguration.cs

代码

using System;
       using System.Net;
       using System.Windows;
       using System.Windows.Controls;
       using System.Windows.Documents;
       using System.Windows.Ink;
       using System.Windows.Input;
       using System.Windows.Media;
       using System.Windows.Media.Animation;
       using System.Windows.Shapes;
       using System.ComponentModel.Composition;
       namespace DynamicExtension
       {
           /// <summary>
           /// 为每个运算器的属性配置值
           /// </summary>
           public class ComponentConfiguration
           {
               [Export("DivisionButtonContract")]
               public string AddLabel { get {  return "Div"; } }
               [Export("DivisionSybomContract")]
               public string AddSymbol { get {  return "/"; } }
           }
       }

5).修改Home.cs ,为其注册下载包的相关事件和回调

1.代码

using System;
       using System.Windows;
       using System.Windows.Controls;
       using System.Windows.Navigation;
       using System.Collections.ObjectModel;
       using System.ComponentModel.Composition.Hosting;
       using System.Reflection;
       using System.ComponentModel.Composition;
       using ContractLibrary;
       namespace MefDemo
       {
           public partial class Home : Page
           {
               [ImportMany(typeof (IOperate),AllowRecomposition = true)]
               public  ObservableCollection<IOperate> Operates = new  ObservableCollection<IOperate>();
               [Export("ClickHandler")]
               public OperateHandler ClickHandler {  get { return OperateButton_Click; } }
               private PackageCatalog Catalog;
               /// <summary>
               /// 用于界面控件响应运算后的一些更新工 作
               /// </summary>
               /// <param name="Operate">运算器 </param>
               public void OperateButton_Click (IOperate Operate)
               {
                   try
                   {
                       Symbol.Text =  Operate.Symbol;
                       double left =  double.Parse(LeftNum.Text);
                       double right =  double.Parse(RightNum.Text);
                       this.Result.Text =  Operate.Op(left, right).ToString();
                   }
                   catch (Exception e)
                   {
                       ChildWindow errorWin =  new ErrorWindow(e);
                       errorWin.Show();
                   }
               }
               public Home()
               {
                   InitializeComponent();
                   this.Loaded += new  RoutedEventHandler(Home_Loaded);
                   //注册按钮事件
                   this.DynamicLoadButton.Click +=  (s, e) =>
                   {
                       //下载包
                       Package.DownloadPackageAsync(
                           new Uri ("DynamicExtension.xap", UriKind.Relative),
                           (args, package)  => Catalog.AddPackage(package)
                       );
                       //包被添加到 PackageCatalog后会自动重新组合
                       //并对添加了 AllowRecomposition = true属性的Import导入器重新输入数据
                   };
               }
               void Home_Loaded(object sender,  RoutedEventArgs e)
               {
                   //组合当前XAP包中所有部件 (Parts)
                   Catalog = new PackageCatalog ();
                   Catalog.AddPackage (Package.Current);
                   CompositionContainer container  = new CompositionContainer(Catalog);
                   container.ComposeParts (this);
                   //组合后所有实现运算接口 (IOperate)的运算器都将被自动填充到 Operates 集合。
                   //将运算器绑定到 ListBox 控件 ,用于呈现。
                   this.operateList.DataContext =  Operates;
               }
               // Executes when the user navigates  to this page.
               protected override void  OnNavigatedTo(NavigationEventArgs e)
               {
               }
           }
       }

Ok,最终界面。

点击DynamicLoadOperate按钮后

程序中还有很多细节没有展开说明,理论性的介绍可以参考MSDN和CodePlex上 的文档。

源码下载:http://download.csdn.net/source/2062158

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