如何触发或抑制Windows虚拟键盘的显示

In WPF I have a screen for login which has a textbox for username and a password box for password. I ideally need to prevent the on-screen keyboard from displaying so I can use a custom keyboard in the perfect location in the app. Failing that I need to somehow force the on-screen keyboard to display for the password box.In WPF I have a screen for login which has a te