The elevation of a button can be changed for a given control state using setElevation:forState:
.
See the Material Design shadow guidelines for a detailed overview of different shadow elevations.
For example, to make a button elevate on tap like a floating action button:
button.setElevation(6, for: .normal)
button.setElevation(12, for: .highlighted)
[button setElevation:6 forState:UIControlStateNormal];
[button setElevation:12 forState:UIControlStateNormal];