Snapkit LayoutConstraints Unable to simultaneously satisfy constraints - ios

Question

I have simple UITableView and custom UITablViewCell in my project, which created programmatically and use SnapKit for auto layout its.
When I run app, everything work fine and get some LayoutConstraints error in debug console.
UITableViewCell
import UIKit
import SnapKit
class TestTableViewCell: UITableViewCell {
...
private lazy var containerView: UIView = {
let view = UIView()
return view
}()
private lazy var centerStackView: UIStackView = {
let stackView = UIStackView(arrangedSubviews: [titleLabel, disclosureImageView])
stackView.axis = .horizontal
stackView.distribution = .fill
stackView.spacing = 5.0
return stackView
}()
private lazy var titleLabel: UILabel = {
let label = UILabel()
label.font = UIFont.systemFont(ofSize: 17, weight: .semibold)
return label
}()
private lazy var disclosureImageView: UIImageView = {
let imageView = UIImageView()
imageView.contentMode = .scaleAspectFit
imageView.image = UIImage(named: "disclosure")
return imageView
}()
..
private func setupUI() {
selectionStyle = .none
backgroundColor = .background
contentView.addSubview(containerView)
containerView.backgroundColor = .white
containerView.layer.cornerRadius = 12
containerView.clipsToBounds = true
containerView.addSubview(centerStackView)
setNeedsUpdateConstraints()
}
// MARK: - Update Constraints
override func updateConstraints() {
containerView.snp.updateConstraints { make in
make.top.bottom.equalToSuperview().inset(8)
make.leading.trailing.equalToSuperview().inset(16)
make.height.equalTo(100)
}
centerStackView.snp.updateConstraints { make in
make.center.equalToSuperview()
}
super.updateConstraints()
}
}
How I can fix this constraint error ?

Answer 1

There are actually two conflicts for each table view cell. You can copy-paste the sets of constraints are in conflict into https://www.wtfautolayout.com and see exactly why they are conflicting. As a result, we get this and this.
We can see that the first conflict is caused by your container view having a height constraint, but the table view itself also adds a height constraint to the cell to enforce its cells' sizes,
"<NSLayoutConstraint:0x7b1400031920 'UIView-Encapsulated-Layout-Height' UITableViewCellContentView:0x7b4c00003640.height == 116.5 (active)>"
For some reason, the constant here is 116.5, not 116 as you would expect from the 100 points of height of the container view + the 16 points of inset.
You can either change it to
make.height.greaterThanOrEqualTo(100)
Or remove the height constraint completely:
// make.height.equalTo(100)
and use the delegate method heightForRowAt to control the cell height instead:
override func tableView(_ tableView: UITableView, heightForRowAt indexPath: IndexPath) -> CGFloat {
116
}
As for the second conflict, it is caused by a constraint constraining the stack view's width to 0, being in conflict with the fact that there must be some spacing between the image and label.
"<NSLayoutConstraint:0x7b1400031b50 'UIView-Encapsulated-Layout-Width' UIStackView:0x7b4c000039c0.width == 0 (active)>"
If you move the following code from updateConstraints into setupUI, the conflict is resolved:
containerView.snp.updateConstraints { make in
make.top.bottom.equalToSuperview().inset(8)
make.leading.trailing.equalToSuperview().inset(16)
make.height.greaterThanOrEqualTo(100)
}
centerStackView.snp.updateConstraints { make in
make.center.equalToSuperview()
}