.Net实现程序的插件机制

　　使用asp.net或vb.net或C#.net均可以实现插件的功能，插件的作用是对系统的后期未知扩展预留快速升级的空间！插件开发完成后将以DLL的形式发布到特定的文件夹中，例如主程序文件夹是D：\myApp\myApp.exe，我们可以在D：\myApp中定义文件夹D：\myApp\Plus目录来存放插件。

　　在程序中通过遍历该文件夹中的所有DLL检测符合预定接口的插件来实现动态装载相应的功能模块！

　　下面举例：

　　一、定义接口

　　新建解决方案用于生成此接口

以下为引用的内容：
1 Public Class IPlugin
2     Public Interface IPlugin
3         Property MovementID() As Integer
4         Property MovementName() As String
5         Property ReTryMinute() As Integer
6         Property ConnectionString() As String
7         Event RaiseLog(ByVal log As String)
8         Sub Init()
9     End Interface
10 End Class

　　二、编写继承自该接口的自定义组件（将编译成DLL）

　　该操作您需要新建一个解决方案

以下为引用的内容：
1

Imports System.Data
2

Imports System.Data.SqlClient
3

Imports System.Net
4

Imports System.IO
5

Imports na7Interface.IPlugin
6

Public Class recv
8

Implements IPlugin '实现此接口
10

'构造属性变量
12

Private _MovementID As Integer = 27
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Private _MovementName As String = "51麦克疯"
14

Private _SpanMinute As Integer = 30
15

Private _ConnectionString As String = ""
16

Private Fir As String = "活动：" + MovementName + "(" + MovementID.ToString + ")"
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''' <summary>
20

''' 返回内部处理的消息,实现接口中的RaiseLog事件。
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''' </summary>
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''' <param name="logText"></param>
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''' <remarks></remarks>
24

Public Event RaiseMyEvent(ByVal logText As String) Implements IPlugin.RaiseLog
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''' <summary>
27

''' 调用此方法！
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''' </summary>
29

''' <remarks></remarks>
30

Public Sub Init() Implements IPlugin.Init '继承自接口的Init方法。
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'这里放置数据抓取及相关的处理程序。
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'实际应用中要根据您的程序何时调用Init决定，这不是必须的方法
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ResultText("处理完成！")
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End Sub
35

Private Sub SaveSetups(ByVal savedate As String, ByVal UserID As String, ByVal WebId As String, ByVal Setups As String)
37

'定义该内部方法，这个方法不实现任何接口中的方法。因此只在本类内部实现。
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Dim CmdText As String = ""
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End Sub
40

''' <summary>
42

''' 返回八位数字的日期格式
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''' </summary>
44

''' <param name="dt"></param>
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''' <returns></returns>
46

''' <remarks></remarks>
47

Private Function ClongDate(ByVal dt As Date) As String '同上
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Dim mm As String = dt.Month.ToString
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If mm.Length = 1 Then mm = "0" + mm
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Dim dd As String = dt.Day.ToString
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If dd.Length = 1 Then dd = "0" + dd
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Return dt.Year.ToString + "" + mm + dd
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End Function
54

Private Function ConvDate(ByVal dt As Long) As String '同上
56

Dim YY As String = Mid(dt.ToString, 1, 4)
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Dim MM As String = Mid(dt.ToString, 5, 2)
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Dim DD As String = Mid(dt.ToString, 7, 2)
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Return YY + "-" + MM + "-" + DD + " 00:00:00"
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End Function
61

''' <summary>
63

''' 获得此组件处理的活动ID,该属性实现了接口IPlugin的MovementID属性。
64

''' </summary>
65

''' <value></value>
66

''' <returns></returns>
67

''' <remarks></remarks>
68

Public Property MovementID() As Integer Implements IPlugin.MovementID
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Get
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Return _MovementID
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End Get
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Set(ByVal value As Integer)
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_MovementID = value
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End Set
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End Property
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''' <summary>
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''' 获得此组件的活动名称,同上
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''' </summary>
80

''' <value></value>
81

''' <returns></returns>
82

''' <remarks></remarks>
83

Public Property MovementName() As String Implements IPlugin.MovementName
84

Get
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Return _MovementName
86

End Get
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Set(ByVal value As String)
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_MovementName = value
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End Set
90

End Property
91

''' <summary>
93

''' 获得此组件定时调用的间隔分钟数，实现自定义属生ReTryMinute
94

''' </summary>
95

''' <value></value>
96

''' <returns></returns>
97

''' <remarks></remarks>
98

Public Property SpanMinute() As Integer Implements IPlugin.ReTryMinute
99

Get
100

Return _SpanMinute
101

End Get
102

Set(ByVal value As Integer)
103

_SpanMinute = value
104

End Set
105

End Property
106

107

Public Property ConnectionString() As String Implements IPlugin.ConnectionString
108

Get
109

Return _ConnectionString
110

End Get
111

Set(ByVal value As String)
112

_ConnectionString = value
113

End Set
114

End Property
115

116

Public Sub ResultText(ByVal txt As String)
117

'响应事件
118

RaiseEvent RaiseMyEvent(txt)
119

End Sub
120

End Class

　　三、在程序中调用定义的接口

　　注意：程序中定义接口编译生成的DLL必须使用同一个，否则如果不是使用相同的DLL，即使DLL的内容相同，同样也会产生错误。

以下为引用的内容：
Imports System.Data
Imports System.Data.SqlClient
Imports System.Reflection
Imports PlusFace.Face

Public Class ShowPlus
    Inherits System.Web.UI.Page
    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        loadPlus()
    End Sub

    Private Sub loadPlus()
        '遍历Plus目录下的dll文件
        dllFileName.Items.Add(New ListItem("请选择接口插件", ""))
        Dim DirPath As String = Server.MapPath("..\Interface")
        If IO.Directory.Exists(DirPath) = False Then
            IO.Directory.CreateDirectory(DirPath)
        End If
        Dim DirectoryPath() As String
        DirectoryPath = System.IO.Directory.GetFileSystemEntries(DirPath)
        For Each file As String In DirectoryPath
            If System.IO.File.Exists(file) = True Then
                '判断此文件扩展名是否为dll
                If LCase(Strings.Right(file, 4)) = ".dll" Then
                    '获得此文件信息及此组件的入口类名称与
                    Dim Ref As Assembly
                    Ref = Assembly.LoadFrom(file)
                    For Each typeTmp As Type In Ref.GetTypes
                        If typeTmp.IsPublic = True Then
                            '下面判断是否实现了接口，如果是，则取当前类型为该类实现的类型
                            Dim TypeGet As Type = typeTmp.GetInterface("Plus")
                            If IsNothing(TypeGet) = False Then
                                Dim asmName As String = System.IO.Path.GetFileNameWithoutExtension(file)
                                Dim t As Type = Ref.GetType(typeTmp.FullName) '这是区分大小写的。
                                Dim Obj As Plus = CType(Activator.CreateInstance(t), Plus)
                                '下面加载插件
                                Dim FileName As String = Replace(file, Server.MapPath("..\Interface\"), "")
                                Response.Write(Obj.InterfaceName + "(" + FileName + ")")
                                Exit For
                            End If
                        End If
                    Next
                End If
            Else
            End If
        Next
    End Sub
End Class

　　这里有本人2007年底花四个月时间写成的进销存系统，里面使用了插件机制生成的报表设计管理器，但没有使用到接口，而是预先定义好调用的方法。

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