Question

I have a sub that handles when 14 ComboBoxes have their Index changed. I am able to cast the sender of the event, and obtain properties from there. However, after that, I want to be able to change the properties of the actual sender, rather than the cast one. How would I do this?

Current code:

Private Sub ComboBoxIndexChange(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ComboBox1.SelectedIndexChanged, ComboBox2.SelectedIndexChanged [etc]
        Dim myComboBox As ComboBox = sender

        Select Case myComboBox.Text
            Case "Will"
                Me.Controls(myComboBox.Name).Text = "555-555-555"
            Case "Bob"
                Me.Controls(myComboBox.Name).Text = "555-124-1234"
            [etc]
        End Select
    End Sub
End Class

As you can see, I am currently trying to use

Me.Controls(myComboBox.Name).Text

But I get the error: Object reference not set to an instance of an object.

What can I do?

Answer 1

The sender parameter in an event handler will (typically) contain a reference to the object that raised the event. In the case of the SelectedIndexChanged event of a ComboBox control, it will be the ComboBox that had its SelectedIndex property changed. So in your code sample above myComboBox is referring the ComboBox that raised the event.

To clarify: if you select an item in the drop-down list of a ComboBox control, so that it raises the SelectedIndexChanged event, the sender parameter of the event handler will be that same ComboBox, not a copy of it. This is true for all reference types.

Had it been a value type raising the event it would have been a completely different story, but that is a very rare case (it it is never the case when it comes to controls on a form).