Set focus on a textbox control in UserControl in wpf

Question

I have created an UserControl which is loaded in a View (Window) in WPF. In my user control I have put a TextBox. I am unable to set focus on this

Answer 1

What i use in my authentication manager:

private void SelectLogicalControl()
{
    if (string.IsNullOrEmpty(TextboxUsername.Text))
        TextboxUsername.Focus();
    else
    {
        TextboxPassword.SelectAll();
        TextboxPassword.Focus();
    }
}

If no username is set, focus on the username-textbox; otherwise the (select all) passwordbox. This is in the codebehind-file, so not viewmodel ;)