Ios-Cocoapds

Mobile Application Programming in iOS

CS-GY9033 Fall 2014 Session 5

AutoLayout

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Layout System that is:

• • •

Constraint-based Dynamic Descriptive

Before AutoLayout

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Hardcoded layout based on Frame

UIView.init(frame: CGRect(x: 0, y: 0, width: 120, height: 240))

Fixed Layout Problems

• • •

Can’t handle rotation well Can’t handle different devices Lots of math and exception

What Layout Do We Want?

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Center of Button == Center of View

Button.center.x == superview.center.x

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Bottom of Button == Bottom of View Padding

Button.bottom == superview.bottom - padding

AutoLayout Demo 1

AutoLayout coding

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Remember simple formula:

item1.attribute = multiplier x item2.attribute + constant

• •

Doesn’t have to be equality (, =) Use the class: NSLayoutConstraint

NSLayoutConstraint

convenience init(item view1: AnyObject!,
        attribute attr1: NSLayoutAttribute,
        relatedBy relation: NSLayoutRelation,
           toItem view2: AnyObject!,
        attribute attr2: NSLayoutAttribute,
       multiplier multiplier: CGFloat,
         constant c: CGFloat)

enum NSLayoutAttribute : Int { case Left case Right case Top case Bottom case Leading case Trailing case Width case Height case CenterX case CenterY case Baseline case NotAnAttribute } enum NSLayoutRelation : Int { case LessThanOrEqual case Equal case GreaterThanOrEqual }

Why NSLayoutConstraint Code?

• • •

Understand the underlying mechanism Runtime constraints (building views dynamically) Sometime you just can’t do it in Interface Builder

Adding Constraints to Views

UIView methods:

func addConstraint(_ constraint: NSLayoutConstraint) func addConstraints(_ constraints: [AnyObject]) func removeConstraint(_ constraint: NSLayoutConstraint) func removeConstraints(_ constraints: [AnyObject])

Where to add Constraints?

• • • •

Closest View object that contains constrained Views Sibling Views => Parent View Cousin Views => Grandparent View...