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