Cause this VB6-like smell, which VB.NET allows, to error instead: WinFormType.InstanceProp=Value [DISABLE My.Forms]

Question

I have notice something very obnoxious with VB.Net\'s treatment of Winform objects.

This has trashed several hours of our time. It will only get worse as we have more

Answer 1

No. This confusing behaviour is by design.

It has been possible in VB to use one instance of a form without creating it, and this behaviour happily made it to VB.NET. To me, this is one of the worst design choices.
But it does make converting legacy projects easier. And it does a favour to those who never even knew a form could be explicitly instantiated.

But you are not required to use this trick, as you never were in VB6. In both languages you can use explicitly created instances, in which case the default instance will not be created. Just forget this "feature" exists and only let it back to your mind when enlightening others.

Answer 2

Sorta. You could create a function or override ShowDialog that checks the My.Forms collection to see if the current instance is in it and if it is thrown an exception. There's not a setting that can be used to prevent it from being used.

EDIT: adding sample code illustrating the concept (using a beep instead of an exception).

    Shared Function FormIsInMyForms(formName As String, frm As Form)
        If formName = "Form1" Then
            If frm.Equals(Form1) Then
                Return True
            Else
                Return False
            End If
        End If
        Return False

    End Function

    Public Overloads Sub ShowDialog()

        If FormIsInMyForms("Form1", Me) Then
            Beep()
        End If

        MyBase.ShowDialog()
    End Sub

Doing the same thing via reflection is left as an exercise for the reader... :)