[RESOLVED] Prevent developer from placing a UserControl more than one time in Design Time

[FunkyDexter]

I don't know of a way to cancel the control creation

Haven't got an ide in front of me to check but you could presumably just remove it:-

f.Controls.Remove(Me)

By the way, I think there's a typo in your code:-

Dim c = f

Should be:-

Dim c = f.GetNextControl(c, True)

Unless you actually want to check the control isn't the form for some reason


edit> crossed over

You may or may not want this:-

If Me.DesignMode

While that's in they could add a second control to the form at run time.

is the same thing?

Not quite. The "On" methods fire the events and are the intended method for firing the event from code, rather than calling the handling event directly. The correct way to wire up an event handler is the first one.

[Simonetos The Greek]

You may or may not want this:-

If Me.DesignMode

While that's in they could add a second control to the form at run time.

Do you mean if developer try to add this control programmatically?

[Simonetos The Greek]

You may or may not want this...

So I ended up on this...

Private Sub Me_ParentChanged(sender As Object, e As EventArgs) Handles Me.ParentChanged
    If Me.ParentForm IsNot Nothing Then
        Dim _UserControl = DirectCast(Me.ParentForm, Control)
        If _UserControl IsNot Nothing Then
            Do Until _UserControl Is Nothing
                If TypeOf _UserControl Is CmosTitleBar AndAlso _UserControl IsNot Me Then
                    Throw New ArgumentOutOfRangeException("", "You can place only one " & _UserControl.Name & " control per form.")
                End If
                _UserControl = _UserControl.GetNextControl(_UserControl, True)
            Loop
        End If
    End If
End Sub

[i00]

So I ended up on this...

Private Sub Me_ParentChanged(sender As Object, e As EventArgs) Handles Me.ParentChanged
        If Me.ParentForm IsNot Nothing Then
            Dim _UserControl = DirectCast(Me.ParentForm, Control)
            If _UserControl IsNot Nothing Then
                Do Until _UserControl Is Nothing
                    If TypeOf _UserControl Is CmosTitleBar AndAlso _UserControl IsNot Me Then
                        Throw New ArgumentOutOfRangeException("", "You can place only one " & _UserControl.Name & " control per form.")
                    End If
                    _UserControl = _UserControl.GetNextControl(_UserControl, True)
                Loop
            End If
        End If
    End Sub

This is incorrect : _UserControl = _UserControl.GetNextControl(_UserControl, True)
... it will only go into controls... look @ my first example...

[Simonetos The Greek]

This is incorrect : _UserControl = _UserControl.GetNextControl(_UserControl, True)
... it will only go into controls... look @ my first example...

Yes but I can't understand this part

Dim c = f

What is f and what is c? If f is the ParentForm and c the UserControl, then why c=f?