Weird issue when setting up auto-layout constraints in code - ios

Question

I want to have a footer view on a static-cell UITableView that has three labels which are equally spaced, like so (from the simulator):
I can supply the footer view from my table view controller using this delegate call:
override func tableView(tableView: UITableView, viewForFooterInSection section: Int) -> UIView? {
// construct view here
return view
}
And I can construct the view in two ways:
Create the labels and the spacers in code and add the appropriate constraints
Do all that in a XIB file then load the view from the file
My problem is that the first approach doesn't work and the second does.
This is my code for the first approach:
override func tableView(tableView: UITableView, viewForFooterInSection section: Int) -> UIView? {
if section == 0 {
// Create footer view
let view = UIView()
view.backgroundColor = UIColor.yellowColor()
view.clipsToBounds = false
view.layer.borderColor = UIColor.greenColor().CGColor
view.layer.borderWidth = 2
view.setTranslatesAutoresizingMaskIntoConstraints(false)
// Create labels
var labels: [UIView] = []
for name in ["Label 1", "AAAAAABBB", "Last label"] {
let v = UILabel()
v.font = UIFont.preferredFontForTextStyle(UIFontTextStyleFootnote)
v.textColor = UIColor.darkTextColor()
v.textAlignment = .Center
v.text = name
v.setTranslatesAutoresizingMaskIntoConstraints(false)
view.addSubview(v)
labels += [v]
}
// Create spacers
var spacers: [UIView] = []
for i in 1...4 {
let v = UIView()
v.backgroundColor = UIColor.blueColor() // Background color is just so we can see where the view is and what size it has
v.setTranslatesAutoresizingMaskIntoConstraints(false)
view.addSubview(v)
spacers += [v]
}
// Constrain all views to top and bottom of superview
for i in labels + spacers {
view.addConstraint(NSLayoutConstraint(item: i, attribute: .Top, relatedBy: .Equal, toItem: view, attribute: .Top, multiplier: 1, constant: 0))
view.addConstraint(NSLayoutConstraint(item: i, attribute: .Bottom, relatedBy: .Equal, toItem: view, attribute: .Bottom, multiplier: 1, constant: 0))
}
// Equal width for labels
labels.pairs {
view.addConstraint(NSLayoutConstraint(item: $0, attribute: .Width, relatedBy: .Equal, toItem: $1, attribute: .Width, multiplier: 1, constant: 0))
}
// Equal width for spacers
spacers.pairs {
view.addConstraint(NSLayoutConstraint(item: $0, attribute: .Width, relatedBy: .Equal, toItem: $1, attribute: .Width, multiplier: 1, constant: 0))
}
view.addConstraint(NSLayoutConstraint(item: view, attribute: .Left, relatedBy: .Equal, toItem: spacers[0], attribute: .Left, multiplier: 1, constant: 0))
view.addConstraint(NSLayoutConstraint(item: spacers[0], attribute: .Right, relatedBy: .Equal, toItem: labels[0], attribute: .Left, multiplier: 1, constant: 0))
view.addConstraint(NSLayoutConstraint(item: labels[0], attribute: .Right, relatedBy: .Equal, toItem: spacers[1], attribute: .Left, multiplier: 1, constant: 0))
view.addConstraint(NSLayoutConstraint(item: spacers[1], attribute: .Right, relatedBy: .Equal, toItem: labels[1], attribute: .Left, multiplier: 1, constant: 0))
view.addConstraint(NSLayoutConstraint(item: labels[1], attribute: .Right, relatedBy: .Equal, toItem: spacers[2], attribute: .Left, multiplier: 1, constant: 0))
view.addConstraint(NSLayoutConstraint(item: spacers[2], attribute: .Right, relatedBy: .Equal, toItem: labels[2], attribute: .Left, multiplier: 1, constant: 0))
view.addConstraint(NSLayoutConstraint(item: labels[2], attribute: .Right, relatedBy: .Equal, toItem: spacers[3], attribute: .Left, multiplier: 1, constant: 0))
view.addConstraint(NSLayoutConstraint(item: spacers[3], attribute: .Right, relatedBy: .Equal, toItem: view, attribute: .Right, multiplier: 1, constant: 0))
return view
}
else {
return nil
}
}
extension Array {
func pairs(block: (Element, Element?)->()) {
if count == 0 { return }
if count == 1 { block(self.first!, nil) }
var last = self[0]
for i in self[1..<count] {
block(last, i)
last = i
}
}
}
This is the result:
Not at all what I was expecting, right?
Now, on to the second method. Instead of posting a bunch of screenshots from Interface Builder, I have created a sample project available here specifically to test this problem. If you open it, the file FooterView.xib contains the footer view constructed in IB that, as far as I know, has exactly the same view structure and auto-layout constraints.
Using that view, like this:
return (NSBundle.mainBundle().loadNibNamed("FooterView", owner: self, options: nil).first as UIView)
yields the result you saw in the first screenshot, which is exactly what I want.
So, with Interface Builder the constraints work as expected. Why doesn't it work when the views & constraints are created in code? What am I missing?

Answer 1

The view's size is unknown at creation time, so setting its setTranslatesAutoresizingMaskIntoConstraintsto true does the trick:
view.setTranslatesAutoresizingMaskIntoConstraints(true)
Result: