Textbox with last focus - vb.net

Question

I have a form with + 50 controls and with key numeric screen to write in only 5 textbox of this form.
I am using this code to write in these textbox using key numeric screen:
Private Sub bt0_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles bt0.Click, bt1.Click, bt2.Click, bt3.Click, bt4.Click, bt5.Click, bt6.Click, bt7.Click, bt8.Click, bt9.Click, btDec.Click
If TypeOf sender Is DevExpress.XtraEditors.SimpleButton Then
txtRefe.Focus()
SendKeys.Send(CType(sender, DevExpress.XtraEditors.SimpleButton).Text)
End If
End Sub
The problem: I need to know which of these 5 textbox had the focus before touching the numerical button
I have seen this code from this post Find out the control with last focus to find last focus:
Private _focusedControl As Control
Private Sub TextBox_GotFocus(ByVal sender As Object, ByVal e As EventArgs)
_focusedControl = DirectCast(sender, Control)
End Sub
Private Sub button1_Click(ByVal sender As Object, ByVal e As EventArgs)
If _focusedControl IsNot Nothing Then
'Change the color of the previously-focused textbox
_focusedControl.BackColor = Color.Red
End If
End Sub
But how I do it in a form with + 50 controls (Controls of many types: buttons, checkbox, combos, textbox, etc.) ?

Answer 1

You can recursively loop through the form's Controls collection and add event handlers.

Answer 2

The simplest and most trivial solution that comes to anyone's mind is to make a flag holding a datatype of your choice. Let's say int, then what you have to do is to update that flag with a different value for each focus event of each textBox. For the sake of simplicity,
When textBox1 gets focused -> set the flag value to 1
when textBox2 gets focused -> set the flag value to 2
when textBox3 gets focused -> set the flag value to 3
when textBox4 gets focused -> set the flag value to 4
when textBox5 gets focused -> set the flag value to 5
Now you are keeping record for the last focused textBox. You can do a switch statement to handle each of the 5 cases we have
Select Case flag
case 1: 'code for textBox1
case 2: 'code for textBox2
case 3: 'code for textBox3
case 4: 'code for textBox4
case 5: 'code for textBox5
End Select