Coordinate

UIView’s property: frame, bounds, center.

frame = bounds + center.

If v2 is a subview of v1, then to center v2 within v1 you could say:

    v2.center = v1.convertPoint(v1.center, fromView:v1.superview)

Layout

TraitCollection and its four properties: displayScale, userInterfaceIdiom, horizontalSizeClass, verticalSizeClass.

Layout is performed in three primary ways: Manual layout, Autoresizing, Autolayout.

1. Autoresizing

Autoseizing is a matter of conceptually assigning a subview “Springs and struts”, A Spring can stretch; a strut can’t.

Autoresizing is simply to set autoresizingMask in code.

1. Autolayout

There are three ways to write autolayout code: NSLayoutConstraint, Anchor notation and visual format notation.