How can I create an interface in VB.NET with implicit implementations

Question

In C# I can create an interface, and when I use the interface the compiler knows that certain interface requirements are fulfilled by the base class. This is probably clearer with an example:

interface FormInterface
{
    void Hide();
    void Show();
    void SetupForm();
}

public partial class Form1 : Form, FormInterface
{
    public Form1()
    {
        InitializeComponent();
    }

    public void SetupForm()
    {

    }
}

The compiler knows that Hide() and Show() are implemented in Form and the above code compiles just fine. I can't figure out how to do this in VB.NET. When I try:

Public Interface FormInterface
    Sub Hide()
    Sub Show()
    Sub SetupForm()
End Interface


Public Class Form1
    Inherits System.Windows.Forms.Form
    Implements FormInterface

    Public Sub SetupForm() Implements FormInterface.SetupForm

    End Sub

End Class

But the Compiler complains that Form1 must implement 'Sub Hide()' for interface 'FormInterface'. Do I actually have to add the following?

Public Sub Hide1() Implements FormInterface.Hide
    Hide()
End Sub

On all my forms, or is a better route creating an abstract base class that has SetupForm() (and how do you do that in VB.NET)?

Answer 1

No, System.Windows.Forms.Form doesn't have the FormInterface implemented, so VB.NET doesn't know they match. VB.NET doesn't do implicit interface implementation, just explicit.

Yes, you should create a base class and implement your interface on that. I would, however, name them slightly different. Perhaps DoShow and DoHide.

Something like this:

Public Class BaseForm
    Inherits System.Windows.Forms.Form
    Implements FormInterface

    Public Sub SetupForm() Implements FormInterface.SetupForm

    End Sub

    Public Sub DoShow() Implements FormInterface.DoSHow
        Me.Show()
    End Sub

    Public Sub DoHide() Implements FormInterface.DoHide
        Me.Hide()
    End Sub

End Class

Else you could by accident do this:

  Public Class BaseForm
    Inherits System.Windows.Forms.Form
    Implements FormInterface

    Public Sub SetupForm() Implements FormInterface.SetupForm

    End Sub

    Public Sub Show() Implements FormInterface.SHow
        Me.Show()
    End Sub

    Public Sub Hide() Implements FormInterface.Hide
        Me.Hide()
    End Sub

End Class

And that will crash and burn.

Don't make the baseclass MustInherit, because the forms designer won't like that.