In Swift, how to use Layout Anchor to set multiple subviews to have the same width (no constant)?

Question

For example, I have a parent view that contains 3 subviews. I am using Layout Anchor programatically and try to achieve following layout

|--subview 1--|--subview 2--|--subview 3--|

Each of the three subviews has equal width. In other words,

subView1.width = subView2.width = subView3.width subView1.width+subView2.width+subView3.width = parentView.width

I know I can possibly to use multiplier to set up the width for subView 1 & subView 2 as:

subView1.widthAnchor.constraintEqualToAnchor(contentView.widthAnchor, multiplier: 1/3).active = true
subView2.widthAnchor.constraintEqualToAnchor(contentView.widthAnchor, multiplier: 1/3).active = true

and subView3 can have leading anchor to be aligned with subView2's trailing anchor.

However, I saw somewhere that Interface Builder can actually assign these three widths to be equal directly (without using constant or multiplier). Is it possible to do the same with Layout Anchor programatically? And how? Thanks.

Answer 1

Here is the complete set of anchors (I've tried myself and it works):

// Create subView1
let subView1 = UIView()
subView1.backgroundColor = UIColor.redColor()
subView1.translatesAutoresizingMaskIntoConstraints = false
contentView.addSubview(subView1)

// Create subView2
let subView2 = UIView()
subView2.backgroundColor = UIColor.blueColor()
subView2.translatesAutoresizingMaskIntoConstraints = false
contentView.addSubview(subView2)

// Create subView3
let subView3 = UIView()
subView3.backgroundColor = UIColor.greenColor()
subView3.translatesAutoresizingMaskIntoConstraints = false
contentView.addSubview(subView3)

subView1.leadingAnchor.constraintEqualToAnchor(contentView.leadingAnchor).active = true
subView1.topAnchor.constraintEqualToAnchor(contentView.topAnchor).active = true
subView1.bottomAnchor.constraintEqualToAnchor(contentView.bottomAnchor).active = true

subView2.topAnchor.constraintEqualToAnchor(contentView.topAnchor).active = true
subView2.bottomAnchor.constraintEqualToAnchor(contentView.bottomAnchor).active = true

subView3.topAnchor.constraintEqualToAnchor(contentView.topAnchor).active = true
subView3.trailingAnchor.constraintEqualToAnchor(contentView.trailingAnchor).active = true
subView3.bottomAnchor.constraintEqualToAnchor(contentView.bottomAnchor).active = true

subView1.trailingAnchor.constraintEqualToAnchor(subView2.leadingAnchor).active = true
subView2.trailingAnchor.constraintEqualToAnchor(subView3.leadingAnchor).active = true

// Add equal width anchors
subView1.widthAnchor.constraintEqualToAnchor(subView2.widthAnchor).active = true
subView2.widthAnchor.constraintEqualToAnchor(subView3.widthAnchor).active = true

Hope this helps. :)