浅谈VB.NET文章系列之一
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)
Next
Dim ty As Type
For Each ty In asm.GetTypes ‘遍历所有类型的信息
Console.WriteLine(ty.FullName)
Next
‘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
Next
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)
Next
'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)
Next
‘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)
Next
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)
Next
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)
Next
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)
Next
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)
Next
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！
相关名词的简单说明：
反射（Reflection）：.Net中获取运行时类型信息的方式
程序集（Assembly）：编译后的.dll和exe文件。可以获得正在运行的装配件信息，也可以动态的加载装配件，以及在装配件中查找类型信息，并创建该类型的实例。
类型（type）：这里的类型区分于值类型与引用类型中的类型，它包括类，枚举，值类型，接口等。
///////////////////////闵峰
