Question

First, please look at this custom Button-inherited UserControl code:

Public Class UserControl1

Dim _Text As String
Dim _Image As Image

<Browsable(True), Description("Gets or sets the text displayed on the button")> _
Overrides Property Text() As String
    Get
        Return _Text
    End Get
    Set(ByVal value As String)
        _Text = value
        MyBase.Text = value
    End Set
End Property

<Browsable(True), Description("Gets or sets the image displayed on the button")> _
Overloads Property Image() As Image
    Get
        Return _Image
    End Get
    Set(ByVal value As Image)
        _Image = value
        'ReDrawMe()
    End Set
End Property

End Class

That’s ALL the code of the UserControl. The Overrides at Text property is OK, but I don’t know why VS tell me I CAN’T use Overrides at Image property, but I can use Overloads. Why? I thought Overloads only use if there’re multiple methods with the same name (different parameters). Two things I still doubt:

1. Why Image is the only property declaration in this class, but it must be called Overloads?
2. The Property doesn’t have any parameter (of course), so how could Overloads possible?

Thanks for reading.

Answer 1

Because the Image property in the ButtonBase class isn’t declared as Overridable you cannot override it in derived classes.

You can shadow the parent declaration (i.e. hide it) by redeclaring it in the deriving class as Shadows or Overloads. The difference between these two is rather small (§1.15.3 in the VB language specification):

• Shadows shadows by name: if a method (or property) is declared Shadows then it shadows all base class methods (or properties) of the same name.

• Overloads shadows by name and signature: it only hides a method of the same name and same signature.

In your case, both result in the same because there is only a single property of that name.

Either way, if the parent property isn’t marked as overridable, then redefining it in a derived class is a bad idea – it won’t work properly when your control is accessed via its base class type.