Windows Forms

private void someControl_SelectedThingChanged(object sender, EventArgs e)
{
    SomeControl someControl = sender as SomeControl;
    SomeThing selectedThing = someControl.SelectedThing;
    ...
}

private void someControl_SelectedThingChanged(object sender, SelectedThingChangedEventArgs e)
{
    SomeThing selectedThing = e.SelectedThing;
    ...
}

Public Class MainForm

    Private Split As SplitContainer = Nothing

    Public Shadows Property IsMdiContainer() As Boolean
        Get
            Return (Split IsNot Nothing)
        End Get
        Set(ByVal value As Boolean)
            If value Then
                If Split Is Nothing Then
                    Split = New SplitContainer
                    Split.Dock = DockStyle.Fill
                    Split.Panel1.BackColor = Color.Aqua
                    Split.Panel2.BackColor = Color.Wheat
                    Me.Controls.Add(Split)
                End If
            Else
                If Split IsNot Nothing Then
                    Me.Controls.Remove(Split)
                    Split = Nothing
                End If
            End If
            Me.Invalidate()
        End Set
    End Property

End Class