Snapkit: crash: Updated constraint could not find existing matching constraint to update

[tcurdt]

New Issue Checklist

• [x] I have looked at the Documentation
• [x] I have read the F.A.Q.
  

  Issue Info

| Info | Value |
| --- | --- |
| Platform | ios |
| Platform Version | 10 |
| SnapKit Version | 0.40.0 (2e4cebf41d8bd0833487381590ed90c38b9a2491) |
| Integration Method | carthage |

Issue Description

I've just migrated my app to Swift3 and hence also switched to version 0.40 unfortunately it now crashes on startup. I am seeing

NSHashTable {
[0] <SnapKit.LayoutConstraint:[email protected]#47 UILabel:0x7faa7bc38770.top == Foo.ReloadView:0x7faa7bc35340.top + 20.0>
}
 NSHashTable {
[0] <SnapKit.LayoutConstraint:[email protected]#47 UILabel:0x7faa7bc38770.top == Foo.ReloadView:0x7faa7bc35340.top + 20.0>
}

fatal error: Updated constraint could not find existing matching constraint to update: <SnapKit.LayoutConstraint:[email protected]#48 UILabel:0x7faa7bc38770.left == Foo.ReloadView:0x7faa7bc35340.left + 20.0>: file /project/Carthage/Checkouts/SnapKit/Source/Constraint.swift, line 233

A stripped down version of the view controller and view looks like this:

class ReloadView: UIView {

    override init(frame: CGRect) {
        super.init(frame: frame)
        configure()
    }

    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        configure()
    }

    convenience init() {
        self.init(frame: CGRect.zero)
    }

    func configure() {

        let label = UILabel()
        let button = UIButton(type: UIButtonType.roundedRect)

        addSubview(label)
        addSubview(button)

        let padding = 20

        label.snp.updateConstraints { make in
            make.top.equalTo(padding)
            make.left.equalTo(self).offset(padding)
            make.right.equalTo(self).offset(-padding)
            make.width.equalTo(300)
        }

        button.snp.updateConstraints { make in
            make.top.equalTo(label.snp.bottom).offset(padding)
            make.left.equalTo(padding)
            make.width.equalTo(self).offset(-2*padding)
            make.bottom.equalTo(0).offset(-padding)
        }
    }
}

class FooViewController: UIViewController {

    private var reloadView: ReloadView!

    override func viewDidLoad() {
        super.viewDidLoad()

        let reloadView = ReloadView()
        self.reloadView = reloadView

        view.addSubview(reloadView)

        reloadView.snp.updateConstraints { make in
            // make.center.equalToSuperview()
            make.edges.equalTo(view.snp.edges)
        }

    }
}

[tcurdt]

Commenting out that view I am off to the next problem:

*** Terminating app due to uncaught exception 'NSInvalidLayoutConstraintException', reason: 'Constraint improperly relates anchors of incompatible types: <SnapKit.LayoutConstraint:[email protected]#84 NSKVONotifying_WKWebView:0x7fb8b482ce00.top == UIView:0x7fb8b3d0ca30.left>'

with the constraints being

        webView.snp.updateConstraints { make in
            // make.edges.equalToSuperview()
            // make.edges.equalTo(view)
            make.edges.equalTo(view.snp.edges)
        }

[tcurdt]

Seems like make.top.left.bottom.right.equalTo(view) does work.

[robertjpayne]

@tcurdt I think this is a dupe of #291

[robertjpayne]

@tcurdt yea this is a dupe of #291, the crasher is due to a new way updateConstraints works that does not allow you to create _new_ constraints if there is already one or more existing constraints from SnapKit on the view.

[tcurdt]

@robertjpayne I've run into another thing that seems related:

targetView.snp.updateConstraints { make in
    make.edges.equalToSuperview().inset(UIEdgeInsets(top: 0, left: 0, bottom: 150, right: 0))
}

let margin = UIEdgeInsets(top: 8, left: 8, bottom: -8, right: -8)

cornerTL.snp.updateConstraints { make in // an UIImageView
    make.top.equalTo(targetView).offset(margin.top)
    make.left.equalTo(targetView).offset(margin.left)
}

results in

fatal error: Updated constraint could not find existing matching constraint to update: <SnapKit.LayoutConstraint:[email protected]#184 UIImageView:0x7fe923426270.left == UIView:0x7fe923649780.left + 8.0>: file /project/Carthage/Checkouts/SnapKit/Source/Constraint.swift, line 233

[robertjpayne]

@tcurdt the error message it accurate, you're attempting to update constraints that do not exist likely (is targetView the same as the original superview?)

[robertjpayne]

@tcurdt wait, this isn't quite right, do you have _any_ other code blocks that do cornerTL.snp.updateConstraints?

[tcurdt]

to give the bigger picture:

let targetView = UIView()
view.addSubview(targetView)

let cornerTL = UIImageView(image: ...)
targetView.addSubview(cornerTL)

targetView.snp.updateConstraints { make in
    make.edges.equalToSuperview().inset(UIEdgeInsets(top: 0, left: 0, bottom: 150, right: 0))
}

let margin = UIEdgeInsets(top: 8, left: 8, bottom: -8, right: -8)

cornerTL.snp.updateConstraints { make in // an UIImageView
    make.top.equalTo(targetView).offset(margin.top)
    make.left.equalTo(targetView).offset(margin.left)
}

and I call cornerTL.snp.updateConstraints only once!

[robertjpayne]

@tcurdt ah yea so the engine is basically seeing the first constraint and failing the second ( the first is entirely new the second is new but there is now 1 constraint in the list ).

I'll probably tweak this internally so if you call updateConstraints and there are 0 constraints it actually runs makeConstraints instead.

[robertjpayne]

@tcurdt fixed on head of feature/0.40.0 branch!

[tcurdt]

Argh! Shouldn't I actually be calling makeConstraints all the time?

[robertjpayne]

@tcurdt you should:

• Use makeConstraints where code executes exactly once OR you need to add more constraints to existing ones
• Use remakeConstraints where you have new attribute combinations (e.g. changing left = right to left = left ) and want to throw away all existing constraints and make new ones
• Use updateConstraints where you have identical attribute combinations and just want to update the constant value (e.g. offset(10) to offset(20)

updateConstraints and remakeConstraints both act like makeConstraints if the from view has no existing constraints created from SnapKit.

[tcurdt]

Yeah, so it was partly my fault. Thanks for all the quick fixing.
Much appreciated in this horrifying upgrade to swift3 :)

[robertjpayne]

@tcurdt no problem, there are some changes specifically updateConstraints is less forgiving than it was on 0.22.0 but that's mostly to avoid headache moving forward.

In most cases updateConstraints is only good for seldomly updating constants, if you are going against a gesture or scroll event you really want to store a reference to the Constraint and use it's update APIs.

[GPF253904828]

v5.0.1

[fukemy]

@GPF253904828 You are not updating the constant; you are trying to assign the constraint to a new anchor