Auto Layout ด้วย NSLayoutConstraint

Hardcoded frames break on different screen sizes and rotations. Auto Layout describes relationships between views — constraints — and the system computes the right frames at runtime.

A constraint is a linear equation: one attribute equals a multiple of another plus a constant. For example, a button's leading edge equals its superview's leading edge plus 20 points.

When adding constraints in code, you must first turn off the old autoresizing system on the view, or constraints will conflict.

The classic API is NSLayoutConstraint constraintWithItem:. It is verbose but explicit.

A constraint does nothing until activated. Use activateConstraints: to turn an array of them on at once.

Modern UIKit offers a cleaner anchor syntax. Each view exposes anchors like leadingAnchor and topAnchor.

Constrain size directly with dimension anchors.

Pin views to the safeAreaLayoutGuide so content stays clear of notches, status bars, and home indicators.

Every constraint has a priority from 1 to 1000. When constraints conflict, lower-priority ones yield. Required constraints are 1000; flexible ones use values like 750.

Views like labels and buttons report an intrinsic content size based on their text. You often only need to pin position, letting the view size itself.

Conflicts print warnings to the console listing the fighting constraints. Use the View Hierarchy Debugger in Xcode to inspect frames and constraints visually.

Test your Auto Layout knowledge.

You learned Auto Layout in UIKit:

• Constraints express relationships, not fixed frames
• Set translatesAutoresizingMaskIntoConstraints = NO
• Create with NSLayoutConstraint or the cleaner anchor API
• Activate constraints and pin to the safe area
• Use priorities and intrinsic size for flexible layouts

Auto Layout makes legacy UIs adapt to every device.