C Sharp与.net学习笔记(四)

接前面MAF，看看MEF插件框架(它是.NET4的组成部分，所以装个Visual C#2010 express)

和 MAF 比起来，这个易用性太高了。只需要定义一个接口，然后Import、Export、Compose就行了...

例子

动手试两个简单的例子：

定义接口 interface.cs

public interface IOperation{    int Operate(int left, int right);}

使用接口 program.cs
- Import
- Compose

using System;using System.ComponentModel.Composition;using System.ComponentModel.Composition.Hosting;class Program{    [Import(typeof(IOperation))]    public IOperation op;    private CompositionContainer container;    private Program()    {        var catalog = new AggregateCatalog();        catalog.Catalogs.Add(new DirectoryCatalog("."));        container = new CompositionContainer(catalog);        container.ComposeParts(this);    }    static void Main(string[] args)    {        Program p = new Program();        Console.Write("Input two number.\n%> ");        string line = Console.ReadLine();        while (line != "q") {            string[] nums = line.Split(' ');            try {                int res = p.op.Operate(int.Parse(nums[0]), int.Parse(nums[1]));                Console.Write("{0}\n%> ", res.ToString());            } catch {                Console.Write("Error!\n%> ");            }            line = Console.ReadLine();        }    }}

实现接口 add.cs
- Export

using System.ComponentModel.Composition;[Export(typeof(IOperation))]class Add : IOperation{    public int Operate(int left, int right)    {        return left + right;    }}

编译：

E:\Test> csc /target:library interface.csE:\Test> csc /r:System.ComponentModel.Composition.dll;interface.dll program.csE:\Test> csc /r:System.ComponentModel.Composition.dll;interface.dll add.cs

例子二

前面的例子使用Import只能导入一个插件(对应一个Export)，如果有多个Export，则运行时会抛出异常。

如果需要导入多个，使用 ImportMany，此时，定义一个额外的接口保存插件接口相关参数

interface.cs

public interface IOperation{    int Operate(int left, int right);}public interface IOperationID{    char ID { get;}}

program.cs

using System;using System.Collections.Generic;using System.ComponentModel.Composition;using System.ComponentModel.Composition.Hosting;class Program{    [ImportMany]    IEnumerable<Lazy<IOperation, IOperationID>> operations;    private CompositionContainer container;    private Program()    {        var catalog = new AggregateCatalog();        //catalog.Catalogs.Add(new AssemblyCatalog(typeof(Program).Assembly));        catalog.Catalogs.Add(new DirectoryCatalog("."));        container = new CompositionContainer(catalog);        container.ComposeParts(this);    }    static void Main(string[] args)    {        Program p = new Program();        foreach (Lazy<IOperation, IOperationID> i in p.operations)        {            Console.WriteLine("{0} {1}", i.Metadata.ID, i.Value.Operate(886, 2).ToString());        }    }}

[Export(typeof(IOperation))][ExportMetadata("ID", '+')]class Add : IOperation{    public int Operate(int left, int right)    {        return left + right;    }}[Export(typeof(IOperation))][ExportMetadata("ID", '-')]class Subtract : IOperation{    public int Operate(int left, int right)    {        return left - right;    }}...

这些Export非常灵活，可以在当前的dll内，也可以在exe内，...

运行结果：

E:\Test> program.exe + 888 - 884 / 443 * 1772

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