The Core iOS Developer’s Cookbook, Fifth Edition

What Are Constraints?

Constraints are rules that allow you to describe your view layout to iOS. They limit how views relate to each other and specify how they may be laid out. With constraints, you can say “these items are always lined up in a horizontal row” or “this item resizes itself to match the height of that item.” Constraints provide a layout language that you add to views to describe geometric relationships.

iOS takes charge of meeting those demands via a constraint satisfaction system. The rules must make sense. A view cannot be both to the left and to the right of another view. One of the key challenges when working with constraints is ensuring that the rules are rigorously consistent. When your rules fail, they fail loudly. Xcode ...