Adding constraints to UITableViewCell contentView - ios

Question

I am trying to add constraints to tableViewCellSubViews, like so -
import UIKit
class SnakeTableViewCell: UITableViewCell {
var lessonViews = Array<UIView>()
override func awakeFromNib() {
super.awakeFromNib()
for var i = 0; i < 3; ++i
{
var view = UIView(frame: CGRectMake(CGFloat(i) * 110.0, 0.0, 100.0, 100.0))
view.backgroundColor = UIColor.redColor()
view.setTranslatesAutoresizingMaskIntoConstraints(false)
self.contentView.addSubview(view)
lessonViews.append(view)
}
self.addConstraints(NSLayoutConstraint.constraintsForEvenDistributionOfViews(lessonViews, relativeToCenterOfView: self, vertically: false))
}
override func setSelected(selected: Bool, animated: Bool) {
super.setSelected(selected, animated: animated)
// Configure the view for the selected state
}
}
And the constraints code -
extension NSLayoutConstraint {
class func constraintsForEvenDistributionOfViews(views:Array<UIView>,relativeToCenterOfView toView:UIView, vertically:Bool ) -> Array<NSLayoutConstraint> {
var constraints = Array<NSLayoutConstraint>()
let attribute = vertically ? NSLayoutAttribute.CenterY : NSLayoutAttribute.CenterX
for (index, view) in enumerate(views) {
let multiplier = CGFloat(2*index + 2) / CGFloat(views.count + 1)
let constraint = NSLayoutConstraint(item: view, attribute: attribute, relatedBy: NSLayoutRelation.Equal, toItem:toView, attribute: attribute, multiplier: multiplier, constant: 0)
constraints.append(constraint)
}
return constraints
}
}
The issue is that when I add the constraints, all the subviews disappears.
Any idea what am I doing wrong ?
Thanks

Answer 1

The multiplier generally is 1. The constant is the variable (horizontal or vertical amount.
You can setup your custom cell, its evenly distributed subViews, and its constraints, all within Storyboard. It's much simpler to do it in Interface Builder, than creating and constraining views in code.
You simply dequeue a reusable cell, and it's already got its properly spaced views, because the cell instantiated and spaced them for you.

Answer 2

You can add constraints to the contentView of a UITableViewCell in init(style:, reuseIdentifier:) as follows (in this case adjusting with an inset of 5pt):
contentView.translatesAutoresizingMaskIntoConstraints = false
contentView.leftAnchor.constraint(equalTo: self.leftAnchor, constant: 5).isActive = true
contentView.topAnchor.constraint(equalTo: self.topAnchor, constant: 5).isActive = true
contentView.rightAnchor.constraint(equalTo: self.rightAnchor, constant: -5).isActive = true
contentView.bottomAnchor.constraint(equalTo: self.bottomAnchor, constant: -5).isActive = true
It works, but... the system will complain:
Changing the translatesAutoresizingMaskIntoConstraints property of the contentView of a UITableViewCell
is not supported and will result in undefined behavior
The warning appears only one time (even though I have multiple cells)
I am doing this to add an inner border and a shadow (without using additional views that will affect the smooth scroll). But the 'not supported' and 'undefined behavior' are things you may consider if you want to use this in a production environment.