xcode button appearing under tabbar

Question

I am using auto layout for everything and I have some buttons that have been snapped into place above the tabbar and in a corner.

The inspector shows no constraints on this button placement. Simulating on a 4 inch screen works fine, but when I simulate on a 3.5 inch screen the button is underneath the tabbar. Why is this happening? The button has "snapped" into place in the corner there so shouldn't auto layout take care of the rest? Or do I need to do something else?

Answer 1

If you have no constraints on an item, then it's placed to a concrete X/Y measured from the top left corner.

If it's in the right location on the 4" screen, then it's at a Y much lower than will look correct on a 3.5" screen. When on a 3.5" screen, the X/Y coordinates will still be measured from the top left corner, 400pixels is much closer to the bottom of a 3.5" screen than it is a 4" screen. If it's 3.5" from the top of the screen on the 4" screen, it won't even be on the screen on the 3.5" screen, etc.

Set your constraints, or adjust the button's location in viewDidLoad based on [[UIScreen mainScreen] bounds].

I recommend the official documentation on autolayout and setting constraints.