The Core iOS Developer’s Cookbook, Fifth Edition

Recipe: Setting Aspect Ratio

Constraint multipliers, the m of the y = m * x + b equation, can help set aspect ratios for your views. Recipe 5-4 demonstrates how to do this by relating a view’s height (y) to its width (x) and setting the m value to the aspect. Recipe 5-4 builds an NSLayoutRelationEqual relationship between the width and height of a view, using the aspect ratio as the multiplier.

The recipe applies its aspect updates by managing a fixed constraint, which it stores locally in an NSLayoutConstraint variable called aspectConstraint. Each time the user toggles the aspect from 16:9 to 4:3 or back, this recipe removes the previous constraint and creates and then stores another one. It builds this new constraint by setting the appropriate ...