18.3 反射示例

1. 动态创建对象

 

CreatingAnObjectDinamically

Imports  System.Reflection

Module  CreatingAnObjectDinamically
     Dim  type  As  Type  =   Assembly .GetExecutingAssembly().GetType( " MyApp.Person " )

     Sub  a()
         Dim  o  As   Object   =   Activator.CreateInstance(type)
        Console.WriteLine( " {0} object has been created " , o.GetType().Name)
     End Sub

     Sub  b()
         Dim  o  As   Object   =  Activator.CreateInstance(type, { " Joe " ,  " Doe " } )
        Console.WriteLine( " {0} object has been created " , o.GetType().Name)
     End Sub

     Sub  c()
         Dim  o  As   Object   =
            type.InvokeMember(name: = "" ,
                              invokeAttr: = BindingFlags.CreateInstance,
                              binder: = Nothing ,
                              target: = Nothing ,
                              args: = { " Joe " ,  " Doe " })

        Console.WriteLine( " {0} object has been created " , o.GetType().Name)
     End Sub

     Sub  d()
         Dim  argTypes()  As  Type  =  { GetType ( String ),  GetType ( String )}
         Dim  ci  As  ConstructorInfo  =  type.GetConstructor(argTypes)
         Dim  o  As   Object   =  ci.Invoke({ " Joe " ,  " Doe " })

        Console.WriteLine( " {0} object has been created " , o.GetType().Name)
     End Sub

     Sub  e()
         Dim  arrType  As  Type  =   GetType ( Double ).MakeArrayType()
         Dim  arr  As  Array  =   DirectCast (Activator.CreateInstance(arrType,  10 ), Array)
         arr.SetValue( 123.45 ,  0 )

        Console.WriteLine( " {0} {1} elements " , arr.Length, arr.GetValue( 0 ).GetType.Name)
        Console.WriteLine( arr.GetValue( 0 ))
     End Sub
End Module

 

 2. 访问成员

 

AccessingMembers

Imports  System.Reflection

Module  AccessingMembers
     Dim  type  As  Type  =   Assembly .GetExecutingAssembly().GetType( " MyApp.Person " )
     Dim  obj  As   Object   =  Activator.CreateInstance(type, { " Joe " ,  " Doe " })

     Sub  f()
         Dim  firstName  As  FieldInfo  =  type.GetField( " FirstName " )        
        firstName. SetValue (obj,  " Robert " )

 

        Console.WriteLine(firstName. GetValue (obj))
     End Sub

     Sub  AgePi()
         Dim  age  As  PropertyInfo  =  type.GetProperty( " Age " )
        age. SetValue (obj: = obj,
                    value: = 35S,
                    index: = Nothing )
        Console.WriteLine(age. GetValue (obj: = obj, index: = Nothing ))
     End Sub

     Sub  NotesPi()
         Dim  notes  As  PropertyInfo  =  type.GetProperty( " Notes " )
        notes. SetValue (obj,  " Tell John about the briefing " , { 1 })

        Console.WriteLine(notes. GetValue (obj, { 1 }))
     End Sub

     Sub  m()
         Dim  mi  As  MethodInfo  =  type.GetMethod( " SendEmail " )
        mi. Invoke (obj, { " This is a message " ,  3 })
        mi. Invoke (obj, { " This is a message " ,  type.Missing })
        mi. Invoke (obj, { " This is a message " , mi.GetParameters( 1 ). DefaultValue })

         Try
            mi.Invoke(obj, { " This is a message " ,  - 1 })
         Catch  ex  As  TargetInvocationException
            Console.WriteLine(ex. InnerException .Message)
         Catch  ex  As  Exception
            Console.WriteLine(ex.Message)
         End   Try

     End Sub
End Module

 3. InvokeMember方法

 

InvokeMember

Imports  System.Reflection

Module  InvokeMember
     Dim  type  As  Type  =   Assembly .GetExecutingAssembly().GetType( " MyApp.Person " )
     Dim  arguments()  As   Object   =  { " Joe " ,  " Doe " }
     Dim  obj  As   Object   =  type.InvokeMember( "" , BindingFlags.CreateInstance,  Nothing ,  Nothing , arguments)

     Sub  InvokeMemberMethod()

        type.InvokeMember(name: = " FirstName " ,
                          invokeAttr: = BindingFlags. SetField,
                          binder: = Nothing ,
                          target: = obj,
                          args: = { " Francesco " })

         Dim  value  As   Object   =
            type.InvokeMember(name: = " FirstName " ,
                              invokeAttr: = BindingFlags. GetField,
                              binder: = Nothing ,
                              target: = obj,
                              args: = Nothing )

        type.InvokeMember(name: = " Age " ,
                          invokeAttr: = BindingFlags. SetProperty,
                          binder: = Nothing ,
                          target: = obj,
                          args: = {35S})

        type.InvokeMember(name: = " SendEmail " ,
                          invokeAttr: = BindingFlags. InvokeMethod,
                          binder: = Nothing ,
                          target: = obj,
                          args: = { " This is a message " ,  2 })

         Dim  age  As   Object   =
            type.InvokeMember(name: = " m_Age " ,
                              invokeAttr: = BindingFlags. GetField  Or  

　　　　　　　　　　　　　　　　　　　　　　　　BindingFlags. NonPublic  Or  BindingFlags. Instance,
                              binder: = Nothing ,
                              target: = obj,
                              args: = Nothing )

        type.InvokeMember(name: = " IncrementValue " ,
                          invokeAttr: = BindingFlags. InvokeMethod,
                          binder: = Nothing ,
                          target: = obj,
                          args: = { 10 })
        Console.WriteLine( " New value for argument = {0} " , { 10 }( 0 ))
     End Sub

End Module

 当调用一个静态成员时:

 

代码

         Dim  count  As   Object   =
            type.InvokeMember(name: = " Count " ,
                              invokeAttr: = BindingFlags.Static  Or  BindingFlags.GetProperty,
                              binder: = Nothing ,
                              target: = Nothing ,
                              args: = Nothing )

 

 

 当只是使用某个方法时请使用单数的Get方法，并尽量为查找函数提供更多的信息：

 

代码

         Dim  mi  As  MethodInfo  =   GetType ( String ).
            GetMethod(name: = " IndexOf " ,
                      bindingAttr: = BindingFlags.ExactBinding  Or
                                   BindingFlags.Public  Or  
                                   BindingFlags.Instance,
                      binder: = Nothing ,
                      types: = { GetType ( Char ),  GetType ( Short )},
                      modifiers: = Nothing )