通过例子，浅谈反射(Reflection)的应用

说明：

应该说这篇短文根本算不上什么深入的分析性的文章，所以在标题前加上了“浅谈”二字，希望对于一般的读者来说，可以给你一个相对直观些的对反射的认识。

--2005/05/23 于东莞

在这里对反射以及反射的概念在最后给出简要的解释。

一．用来测试的程序集文件的建立。

首先你需要建立一个类库文件（编译后扩展名为.dll），名字假设为：reflection_newtest

系统会默认地新建一个类文件class1，把它该成我们用来测试的类person

具体代码如下：(类的代码比较简单，这里不做解释，如有不明之处，请查看类的相关文档.)

Public Class person

Public firstname As String

Public lastname As String

Dim m_age As Short

Dim m_emailaddress(4) As String

Public Sub New()

MyBase.new()

End Sub

Public Sub New(ByVal firstname As String, ByVal lastname As String)

Me.firstname = firstname

Me.lastname = lastname

End Sub

Public Property age() As Short

Get

Return m_age

End Get

Set(ByVal Value As Short)

m_age = Value

End Set

End Property

Public Property emailaddress(ByVal index As Short) As String

Get

Return m_emailaddress(index)

End Get

Set(ByVal Value As String)

m_emailaddress(index) = Value

End Set

End Property

Sub sendemail(ByVal msg As String, Optional ByVal priorty As Integer = 1)

Console.WriteLine("message to " & firstname & " " & lastname)

Console.WriteLine("priority " & priorty.ToString)

Console.WriteLine(msg)

End Sub

End Class

二．测试验证的程序

建立一个winform的程序，命名假设为：testreflection

从工具栏里拖两个按钮，命名为button1,button2.

1．在程序的最上面加入引用：

Imports System

Imports System.Reflection

Imports System.Type

2．在button1的click事件里写：

Dim asm As [Assembly] ‘由于assembly是关键字，所以要加[]

asm = Reflection.Assembly.LoadFrom("G:\练习\reflection_newtest\bin\reflection_newtest.dll") ‘这里假设上面的reflection_newtest文件的位置在G:\练习的文件夹。

Console.WriteLine(asm.FullName) ‘输出完全限定名

Console.WriteLine(asm.Location) ‘获取该文件的基本代码格式的位置

Console.WriteLine(asm.CodeBase) ‘获取最初指定的程序集的位置，一般来说和Location方法很相似

Dim mo As [Module] ‘遍历模块

For Each mo In asm.GetModules

Console.WriteLine(mo.FullyQualifiedName)

Dim ty As Type

For Each ty In asm.GetTypes ‘遍历所有类型的信息

Console.WriteLine(ty.FullName)

‘动态加载一个实例

Dim o As Object = asm.CreateInstance("reflection_newtest.person")

Console.WriteLine("********************")

Console.WriteLine(o.GetType.FullName)

说明：这里的使用都比较简单，请继续往下看！

3．建立测试的过程

'获取遍历的类型，这里使用了系统类库文件mscorlib.dll

Private Sub testtypeenumeration()

Dim asm As [Assembly] = Reflection.Assembly.Load("mscorlib")

Dim t As Type

For Each t In asm.GetExportedTypes ‘对于当前的文件的测试

If t.IsClass Then ‘如果是类

Console.WriteLine(t.Name & "(class)")

ElseIf t.IsEnum Then ‘如果是枚举

Console.WriteLine(t.Name & "(enum)")

ElseIf t.IsValueType Then ‘如果是值类型

Console.WriteLine(t.Name & "(structure)")

ElseIf t.IsInterface Then ‘如果是接口

Console.WriteLine(Name & "(interface)")

Else ‘其他

'没做处理

End If

End Sub

'获取某一类型的所有信息(这里以string为例)

‘从上面的load与type.gettype可见，他们都是创建assembly的方式

Private Sub testatypememberinfo1()

Dim stringtype As Type = Type.GetType("System.String") '获取指定名称的系统类型，也可以使用type.gettype(string)

Dim minfos() As MemberInfo ‘类型数组

Dim mi As MemberInfo

minfos = stringtype.GetMembers

For Each mi In minfos

Console.WriteLine(mi.Name)

'获得公共的非共享的并且是继承的成员

minfos = stringtype.GetMembers(BindingFlags.Public Or BindingFlags.Instance Or BindingFlags.DeclaredOnly)

‘为了便于看清楚输出，做了间隔

Console.WriteLine("*********************")

For Each mi In minfos

Console.WriteLine(mi.Name)

‘同样的间隔设置

Console.WriteLine("*********************")

'获取所有方法

For Each mi In stringtype.GetMethods

Console.WriteLine(mi.Name)

End Sub

'使用特定的显示某一种类型的方法

Private Sub testatypememberinfo()

Dim stringtype As Type = Type.GetType("System.String") '获取指定名称的系统类型

‘对于特定类型的属性的遍历

Dim pinfos() As PropertyInfo = stringtype.GetProperties

Dim mi As MemberInfo

For Each mi In pinfos

Console.WriteLine(mi.Name)

End Sub

'使用findmember方法对类型的遍历1

Private Sub testfindmember1()

Dim stringtype As Type = Type.GetType("System.String")

‘对于findmembers方法来说，它的参数分别为要获得的类型（可用or组合），筛选条件（可用or组合），

委托函数，传递给委托函数的参数。

Dim minfos() As MemberInfo = stringtype.FindMembers(MemberTypes.Method _

Or MemberTypes.Property, BindingFlags.Instance Or BindingFlags.Public, _

AddressOf filterbyname1, "C")

Dim mi As MemberInfo

For Each mi In minfos

Console.WriteLine(mi.Name)

End Sub

'委托函数一：筛选那些是以C开头的公共的实例的方法和属性（这个函数一旦返回true，意味着是符合要求的）

Private Function filterbyname1(ByVal m As MemberInfo, ByVal filtercriteria As Object) As Boolean

'如果成员名称以筛选函数的第2个参数开始，则返回true

If m.Name.StartsWith(filtercriteria.ToString) Then

Return True

End If

End Function

'使用findmember方法对类型的遍历2

Private Sub testfindmember2()

Dim returntype As Type = Type.GetType("System.Int32")

Dim minfos() As MemberInfo = returntype.FindMembers(MemberTypes.Method Or MemberTypes.Property, _

BindingFlags.Instance Or BindingFlags.Public, AddressOf filterbyname2, returntype)

Dim mi As MemberInfo

For Each mi In minfos

Console.WriteLine(mi.Name)

End Sub

'委托函数二

Private Function filterbyname2(ByVal m As MemberInfo, ByVal filtercriteria As Object) As Boolean

If m.MemberType = MemberTypes.Property Then

Dim pi As PropertyInfo = CType(m, PropertyInfo)

Return (pi.PropertyType Is filtercriteria) '如果该属性的类型与第2个参数相同则返回true

ElseIf m.MemberType = MemberTypes.Method Then

Dim mi As MethodInfo = CType(m, MethodInfo)

Return (mi.ReturnType Is filtercriteria) '如果该方法的返回类型与第2个参数相同则返回true

End If

End Function

'关于重载函数的调用

Private Sub testoverloadmemberinfo()

Dim stringtype As Type = Type.GetType("System.String")

'一个类型数组

Dim argtypes() As Type = {Type.GetType("System.String"), Type.GetType("System.String")}

Dim mi As MemberInfo = stringtype.GetMethod("Compare", argtypes)

Console.WriteLine(mi.Name)

End Sub

'枚举参数类型

Private Sub testcallingsyntax()

Dim stringtype As Type = Type.GetType("System.String")

Dim mi As MethodInfo = stringtype.GetMethod("Copy")

Dim pinfos() As ParameterInfo = mi.GetParameters

Dim i As Integer

'列出参数和参数的类型,中间用/连接

For i = 0 To pinfos.GetUpperBound(0)

Console.WriteLine(pinfos(i).Name & "/" & pinfos(i).ParameterType.ToString)

End Sub

'使用反射创建实例并给属性赋值

Private Sub testreadwriteproperties()

Try

Dim asm As [Assembly] = Reflection.Assembly.LoadFrom("G:\练习\reflection_newtest\bin\reflection_newtest.dll")

Dim ty As Type = asm.GetType("reflection_newtest.person")

Dim m As Object = Activator.CreateInstance(ty)

Dim pi As PropertyInfo = ty.GetProperty("age")

pi.SetValue(m, 5S, Nothing) '一定要指定赋值的类型，如是short类型，一定要加s

Console.WriteLine(pi.GetValue(m, Nothing))

Catch ex As Exception

MessageBox.Show(ex.Message)

End Try

End Sub

'测试字符串属性(且含参数)

Private Sub testreadwritepropertytieswithargs()

Try

Dim asm As [Assembly] = Reflection.Assembly.LoadFrom("G:\练习\reflection_newtest\bin\reflection_newtest.dll")

Dim ty As Type = asm.GetType("reflection_newtest.person")

Dim m As Object = Activator.CreateInstance(ty)

Dim pi As PropertyInfo = ty.GetProperty("emailaddress")

Dim params() As Object = {1S} '注意参数类型的严格匹配

pi.SetValue(m, "321 north street", params)

321 north street", params)

Console.WriteLine(pi.GetValue(m, params))

Catch ex As Exception

MessageBox.Show(ex.Message)

End Try

End Sub

'使用invoke方法测试过程

Private Sub testinvokemethod()

Dim asm As [Assembly] = Reflection.Assembly.LoadFrom("G:\练习\reflection_newtest\bin\reflection_newtest.dll")

Dim ty As Type = asm.GetType("reflection_newtest.person")

Dim m As Object = Activator.CreateInstance(ty)

Dim mi As MethodInfo = ty.GetMethod("sendemail")

'定义过程的参数数组

Dim params(mi.GetParameters.Length - 1) As Object

Try

params(0) = "this is message"

params(1) = 3

'触发过程

mi.Invoke(m, params)

Catch ex As Exception

MessageBox.Show(ex.Message)

End Try

End Sub

'使用invokemember方法测试过程

Private Sub testinvokemember()

Dim asm As [Assembly] = Reflection.Assembly.LoadFrom("G:\练习\reflection_newtest\bin\reflection_newtest.dll")

Dim ty As Type = asm.GetType("reflection_newtest.person")

Dim m As Object = Activator.CreateInstance(ty)

Dim args() As Object = {"francesco"}

Try

'设置firstname字段值

ty.InvokeMember("firstname", BindingFlags.SetField, Nothing, m, args)

'读取firstname字段值，这个时候不用最后一个参数

Dim value As Object = ty.InvokeMember("firstname", BindingFlags.GetField, Nothing, m, Nothing)

Console.WriteLine(value.ToString)

Dim args2() As Object = {35S} '注意这里的数组元素的类型一定要严格匹配short类型,

'设置属性值，参数意味着是属性的参数

ty.InvokeMember("age", BindingFlags.SetProperty, Nothing, m, args2)

'读取属性值

Dim value1 As Object = ty.InvokeMember("age", BindingFlags.GetProperty, Nothing, m, Nothing)

Console.WriteLine(value1.ToString)

Dim args3() As Object = {"this is a message", 2}

'触发过程

ty.InvokeMember("sendemail", BindingFlags.InvokeMethod, Nothing, m, args3)

Catch ex As Exception

MessageBox.Show(ex.Message)

End Try

End Sub

‘///////////////////////////////////////////////////////////

'动态地创建对象(使用默认地构造函数)

Private Sub testobjectcreation1()

Dim asm As [Assembly] = Reflection.Assembly.LoadFrom("G:\练习\reflection_newtest\bin\reflection_newtest.dll")

Dim ty As Type = asm.GetType("reflection_newtest.person")

Try

Dim m As Object = Activator.CreateInstance(ty)

Console.WriteLine("A {0} object has been created ", m.GetType.Name)

Catch ex As Exception

MessageBox.Show(ex.Message)

End Try

End Sub

'使用带参数的方法(使用带参数的构造函数)

Private Sub testobjectcreation2()

Dim asm As [Assembly] = Reflection.Assembly.LoadFrom("G:\练习\reflection_newtest\bin\reflection_newtest.dll")

Dim ty As Type = asm.GetType("reflection_newtest.person")

Dim params() As Object = {"Joe", "Doe"}

Try

Dim o As Object = System.Activator.CreateInstance(ty, params)

Console.WriteLine(o.GetType.Name)

Catch ex As Exception

MessageBox.Show(ex.Message)

End Try

End Sub

'使用调用构造函数的方法来创建对象（实例）这个方法相对来说比较烦琐和麻烦。

Private Sub testobjectcreation3()

Dim asm As [Assembly] = Reflection.Assembly.LoadFrom("G:\练习\reflection_newtest\bin\reflection_newtest.dll")

Dim ty As Type = asm.GetType("reflection_newtest.person")

Dim types() As Type = {GetType(System.String), GetType(String)}

Dim ci As ConstructorInfo = ty.GetConstructor(types) '获得这个有两个字符串参数的构造函数的信息

Dim params() As Object = {"Joe", "Doe"} '用来初始化的数组

Dim o As Object = ci.Invoke(params) '执行这个构造函数

Console.WriteLine(o.GetType.Name)

End Sub

4. button2的click事件中写：（该操作就是验证所有的测试过程，为了分辨出是哪个过程的结果，把其他的都暂时注释掉了。你可以根据需要来消除注释。）

'testtypeenumeration()

'testatypememberinfo1()

'testatypememberinfo2()

'testfindmember1()

'testfindmember2()

testoverloadmemberinfo()

'testcallingsyntax()

'testreadwriteproperties()

'testreadwritepropertytieswithargs()

'testinvokemethod()

'testinvokemember()

'testobjectcreation1()

'testobjectcreation2()

'testobjectcreation3()

说明：这里不多做过多地解释，代码中有比较完整的注释。如果有什么疏漏和错误，请指出！谢谢！