Write a value to a textbox depending on variable

Hello,

I have a WPF form and created a stackpanel with 5 textboxes. (TXT1, TXT2, TXT3 ....)
I want to fill these textboxes with a name out of a Global var named "NamePerson" and the textbox depending of the value of i.

Private Sub Button_Click(sender As Object, e As RoutedEventArgs)
Stackpanel1.Children.Item(i).SetValue(NamePerson)
End Sub

Can anyone tell me how i can fix this?

Thanks in advance,

Erika