I would like to center four buttons horizontally and vertically.
Each of the buttons shall get a background image later, so I think it's important that the aspect ratio stays more or less the same, otherwise the pictures won't fit onto the button.
All buttons have the same size and should take up as much space as available (small margin, 10px or so, not more if possible). I don't know how to set the constraints that the application looks good on all devices (iPhone 5s and iPad 10.5").
The application must not necessarily run in all orientation modes.
How do I have to set the constraints?