Multiple buttons, one event to change clicked button colour - vb.net

Question

The code shown below should allow any button on the page to change colour except for the ones named in the first if statement. This code was working but now does nothing when the button is clicked. The button should turn yellow but just stays the default colour. Also is there anyway I can manipulate the code so only one button can be red at a time instead of allowing multiple red buttons. When reading into this. I cannot find any help for vb. Can anyone help?
Personally, I think it may be to do with thePublic Sub since the message box does not appear when a field is empty.
Public Sub btn_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles MyBase.Click
Try
Dim btn As Button = sender
If btn.Name = "BtnUpdate" Or btn.Name = "BtnBackCust" Or btn.Name = "BtnConfirm" Then
ElseIf TxtFirstName.Text = "" Or TxtLastName.Text = "" Or TxtAddress.Text = "" Or cboCountry.SelectedItem = "" Or cboRoomType.SelectedItem = "" Then
MsgBox("You must populate all fields")
Else
btn.BackColor = Color.Red
btn.Text = ChosenRoom
End If
Catch ex As Exception
End Try
End Sub

Answer 1

Instead of using the MyBase.Click Event, create an Handle for each Button on your Form Load:
Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
For Each Button As Button In Me.Controls.OfType(Of Button)()
If Button.Name <> "BtnUpdate" AndAlso Button.Name <> "BtnBackCust" AndAlso Button.Name <> "BtnConfirm" Then
AddHandler Button.Click, AddressOf ChangeColor
End If
Next
End Sub
The ChangeColor sub, also create the RedButton variable to keep track of what is the currently red button:
Private RedButton As Button = Nothing
Private Sub ChangeColor(Sender As Object, e As EventArgs)
If TypeOf Sender Is Button Then
If TxtFirstName.Text = "" OrElse TxtLastName.Text = "" OrElse TxtAddress.Text = "" OrElse cboCountry.SelectedItem = "" OrElse cboRoomType.SelectedItem = "" Then
MsgBox("You must populate all fields")
Else
Dim SenderButton As Button = Sender
If RedButton IsNot Nothing Then
RedButton.BackColor = Me.BackColor
End If
If SenderButton IsNot RedButton Then 'This if will toogle the button between Red and the Normal color
SenderButton.BackColor = Color.Red
End If
RedButton = Sender
End If
End If
End Sub