VB .net Change text of selected textbox on button click - vb.net

Question

I have 10 buttons and I want to click on a button so it changes text of the focused textbox and switch to next textbox.
i tried this:
Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
TextBox1.Focus()
End Sub
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
If TextBox1.Focus Then
TextBox1.Text = "1"
TextBox1.Enabled = False
TextBox2.Focus()
TextBox2.Enabled = True
End If
If TextBox2.Focus Then
TextBox2.Text = "1"
TextBox2.Enabled = False
TextBox3.Focus()
TextBox3.Enabled = True
End If
If TextBox3.Focus Then
TextBox3.Text = "1"
TextBox3.Enebled= False
TextBox4.Focus()
TextBox4.Enabled = True
End If
End Sub
But it writes the value in every textbox instead of just going to the next textboxt

Answer 1

This code does not do what you think it does:
If TextBox1.Focus Then
Focus is not a boolean property. In VB.Net, you can call methods without parentheses, and that's what you're doing here. The conditional block actually tries to set the focus. And since this is always gonna succeed unless you explicitly handle the event and block it, all of those If conditions result in True.
To find which control has focus, do this:
Public Shared Function FindFocusedControl(control As Control) As Control
Dim container = TryCast(control,IContainerControl)
While container IsNot Nothing
control = container.ActiveControl
container = TryCast(control, IContainerControl)
End While
Return control
End Function

Answer 2

In your Click event handler, you are calling the Focus method of each TextBox in turn and then populating them if it succeeds. It will succeed every time so you populate every TextBox.
I suspect that what you meant to do was test the Focused property rather than call the Focus method. That would make more sense because then it would only populate the TextBox that had focus. That is still flawed though, because the Button that you just clicked will have focus, so you won't actually populate any TextBox.
You have two main choices here. Firstly, you could use a custom Button control that will not take focus when it is clicked. That way, the TextBox that had focus when you clicked will still have focus. Alternatively, you could remember which control last had focus by assigning it to a field and using that. That's probably the way that I'd go.
Here's a quick (i.e. not rigorous) example of the second option:
Private lastActiveControl As Control
Private Sub TextBoxes_Leave(sender As Object, e As EventArgs) Handles TextBox4.Leave,
TextBox3.Leave,
TextBox2.Leave,
TextBox1.Leave
lastActiveControl = DirectCast(sender, Control)
End Sub
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
Dim textBoxes = New Control() {TextBox1, TextBox2, TextBox3, TextBox4}
Dim lastTextBoxIndex = Array.IndexOf(textBoxes, lastActiveControl)
If lastTextBoxIndex <> -1 Then
Dim nextTextBoxIndex = (lastTextBoxIndex + 1) Mod textBoxes.Length
Dim nextTextBox = textBoxes(nextTextBoxIndex)
lastActiveControl.Text = "1"
lastActiveControl.Enabled = False
nextTextBox.Enabled = True
nextTextBox.Select()
End If
End Sub