VB.net无法继承

Question

I am fairly new to VB.net, I cannot compile this code, and I don't get why.

MustInherit Class Poligono

    Protected p_cant_Lados As Integer
    Public Property cant_Lados() As Integer
        Get
            Return p_cant_Lados
        End Get
        Set(ByVal value As Integer)
            p_cant_Lados = value
        End Set
    End Property

    Public MustOverride Function obtenerPerimetro()
    Public MustOverride Function cargarLados()

End Class

Public Class Triangulo
    Inherits Poligono

    Private lado1 As Integer
    Private lado2 As Integer
    Private lado3 As Integer

    Public Function cargarLados() As Object
        Return 1
    End Function

    Public Function obtenerPerimetro() As Object
        Return 1
    End Function

End Class

Error 2 'Triangulo' cannot inherit from class 'Poligono' because it expands the access of the base class outside the assembly. c:\\users\\win7\\documents\\visual studio 2013\\Projects\\WindowsApplication1\\WindowsApplication1\\Form1.vb 33 14 WindowsApplication1

Thanks!

Answer 1

By default, classes declared at the namespace level get Friend access level . So Poligono is Friend Class . A Friend class may not be made visible to general public.

Change

MustInherit Class Poligono

to

Public MustInherit Class Poligono

Answer 2

Two things:

1. You have to add the return type with As

    Public MustOverride Function obtenerPerimetro() As Object Public MustOverride Function cargarLados() As Object 

2. You have to add Overrides to the method that overrides the abstract base class

    Public Overrides Function cargarLados() As Object Return 1 End Function Public Overrides Function obtenerPerimetro() As Object Return 1 End Function