为什么接口没有强类型？

Question

我有以下代码编译没有问题.当然,我在执行时遇到了无效的强制转换异常Dim C As IDoThingsC = GetThing_C().我错过了什么吗？您是否希望返回不符合函数返回值的接口要求的对象？

Public Class ClassA

  Public Sub DoThings_A()
    Debug.Print("Doing A things...")
  End Sub

End Class


Public Class ClassB
  Implements IDoThingsC

  Public Sub DoThings_B()
    Debug.Print("Doing B things...")
  End Sub

  Public Sub DoThings_C() Implements IDoThingsC.DoThings_C
    Debug.Print("Doing C things...")
  End Sub

End Class


Public Interface IDoThingsC

  Sub DoThings_C()

End Interface


Public Class aTest

  Public Sub Test()

    Dim C As IDoThingsC = GetThing_C()
    C.DoThings_C()

  End Sub


  Public Function GetThing_C() As IDoThingsC

    Dim Thing As ClassA = New ClassA
    Thing.DoThings_A()

    Return Thing

  End Function


End Class

Answer 1

Option Strict On在源代码文件的顶部使用来捕获这样的问题.您将收到编译时错误而不是运行时错误:

error BC30512: Option Strict On disallows implicit conversions from 'ClassA' to 'IDoThingsC'.