Custom view (xib) with constraints causing crash

Question

I have a problem when adding NewsAndInformationDetailCommentView a custom view (from xib), as a subview of another view.

Inside this custom view, there are some components added with few constraints on each respective component.

Here the custom view code.

import UIKit

class NewsAndInformationDetailCommentView: UIView {

    @IBOutlet weak var view: UIView!

    // the subviews
    @IBOutlet weak var profileImageView: UIImageView!
    @IBOutlet weak var createdByLabel: UILabel!
    @IBOutlet weak var comment: UITextView!
    @IBOutlet weak var createdAtLabel: UILabel!

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

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

    private func prepare() {
        let view = Bundle.main.loadNibNamed(String(describing: NewsAndInformationDetailCommentView.self), owner: self, options: nil)?[0] as! UIView
        self.addSubview(view)

        view.backgroundColor = .clear
        view.frame = self.frame
        view.translatesAutoresizingMaskIntoConstraints = false
        view.addConstraints([
            NSLayoutConstraint(item: view, attribute: .leading, relatedBy: .equal, toItem: self, attribute: .leading, multiplier: 1.0, constant: 0),
            NSLayoutConstraint(item: view, attribute: .trailing, relatedBy: .equal, toItem: self, attribute: .trailing, multiplier: 1.0, constant: 0),
            NSLayoutConstraint(item: view, attribute: .top, relatedBy: .equal, toItem: self, attribute: .top, multiplier: 1.0, constant: 0),
            NSLayoutConstraint(item: view, attribute: .bottom, relatedBy: .equal, toItem: self, attribute: .bottom, multiplier: 1.0, constant: 0)
        ])
    }
}

And here is the screenshot of the xib.

On the parent view this is how the subview is being added. It's pretty straightforward.

let commentView = NewsAndInformationDetailCommentView(frame: CGRect(x: 0, y: previousItem.frame.origin.y + previousItem.frame.size.height, width: contentOfScrollView.frame.size.width, height: defaultHeight))
contentOfScrollView.addSubview(commentView)

When I run the application, it crashed. And below stacktrace appear.

2019-08-03 15:52:23.179570+0700 Satpam Mantab[44304:1673267] [LayoutConstraints] The view hierarchy is not prepared for the constraint: <NSLayoutConstraint:0x600001628dc0 H:|-(0)-[UIView:0x7fc9444401d0]   (inactive, names: '|':Satpam_Mantab.NewsAndInformationDetailCommentView:0x7fc94462a220 )>
    When added to a view, the constraint's items must be descendants of that view (or the view itself). This will crash if the constraint needs to be resolved before the view hierarchy is assembled. Break on -[UIView(UIConstraintBasedLayout) _viewHierarchyUnpreparedForConstraint:] to debug.
------- Optional(<Satpam_Mantab.NewsAndInformationDetailCommentView: 0x7fc94462a220; frame = (0 523; 320 200); layer = <CALayer: 0x600003508b80>>)
2019-08-03 15:52:23.190358+0700 Satpam Mantab[44304:1673267] [LayoutConstraints] View hierarchy unprepared for constraint.
    Constraint: <NSLayoutConstraint:0x600001628dc0 H:|-(0)-[UIView:0x7fc9444401d0]   (active, names: '|':Satpam_Mantab.NewsAndInformationDetailCommentView:0x7fc94462a220 )>
    Container hierarchy: 
<UIView: 0x7fc9444401d0; frame = (0 523; 320 200); autoresize = RM+BM; layer = <CALayer: 0x600003503400>>
   | <UITextView: 0x7fc9460a6000; frame = (60 31; 343 49); text = 'Lorem Lorem Lorem Lorem L...'; clipsToBounds = YES; autoresize = RM+BM; gestureRecognizers = <NSArray: 0x600003b33c90>; layer = <CALayer: 0x600003502c40>; contentOffset: {0, 0}; contentSize: {343, 41}; adjustedContentInset: {0, 0, 0, 0}>
   |    | <<_UITextContainerView: 0x7fc94443eaf0; frame = (0 0; 343 49); layer = <__UITextTiledLayer: 0x60000117f7e0>> minSize = {0, 0}, maxSize = {1.7976931348623157e+308, 1.7976931348623157e+308}, textContainer = <NSTextContainer: 0x60000076c900 size = (343.000000,inf); widthTracksTextView = YES; heightTracksTextView = YES>; exclusionPaths = 0x600003770050; lineBreakMode = 0>
   | <UIView: 0x7fc9444403b0; frame = (15 15; 384 40); autoresize = RM+BM; layer = <CALayer: 0x600003503420>>
   |    | <UIView: 0x7fc944440590; frame = (0 0; 40 40); autoresize = RM+BM; layer = <CALayer: 0x600003503440>>
   |    |    | <UIImageView: 0x7fc94443ffa0; frame = (0 0; 40 40); clipsToBounds = YES; autoresize = RM+BM; userInteractionEnabled = NO; layer = <CALayer: 0x600003503020>>
   |    | <UILabel: 0x7fc944521480; frame = (50 0; 39 20); text = 'admin'; opaque = NO; autoresize = RM+BM; userInteractionEnabled = NO; layer = <_UILabelLayer: 0x6000016221c0>>
   | <UILabel: 0x7fc94443f820; frame = (65 80; 334 20); text = '15 Juli 2019'; opaque = NO; autoresize = RM+BM; userInteractionEnabled = NO; layer = <_UILabelLayer: 0x600001622080>>
    View not found in container hierarchy: <Satpam_Mantab.NewsAndInformationDetailCommentView: 0x7fc94462a220; frame = (0 523; 320 200); layer = <CALayer: 0x600003508b80>>
    That view's superview: <UIView: 0x7fc9446042c0; frame = (0 -400; 320 1000); autoresize = RM+BM; layer = <CALayer: 0x600003523260>>
2019-08-03 15:52:23.217853+0700 Satpam Mantab[44304:1673267] *** Terminating app due to uncaught exception 'NSGenericException', reason: 'Unable to install constraint on view.  Does the constraint reference something from outside the subtree of the view?  That's illegal. constraint:<NSLayoutConstraint:0x600001628dc0 H:|-(0)-[UIView:0x7fc9444401d0]   (active, names: '|':Satpam_Mantab.NewsAndInformationDetailCommentView:0x7fc94462a220 )> view:<UIView: 0x7fc9444401d0; frame = (0 523; 320 200); autoresize = RM+BM; layer = <CALayer: 0x600003503400>>'
*** First throw call stack:
(
    0   CoreFoundation                      0x00000001105ec8db __exceptionPreprocess + 331
    1   libobjc.A.dylib                     0x000000010fb8fac5 objc_exception_throw + 48
    2   CoreFoundation                      0x00000001105ec735 +[NSException raise:format:] + 197
    3   Foundation                          0x000000010f7e7943 -[NSLayoutConstraint _addToEngine:mutuallyExclusiveConstraints:] + 205
    4   UIKitCore                           0x000000011959bce6 __57-[UIView(AdditionalLayoutSupport) _switchToLayoutEngine:]_block_invoke_2 + 456
    5   Foundation                          0x000000010f7d0f46 -[NSISEngine withBehaviors:performModifications:] + 110
    6   UIKitCore                           0x000000011959baf7 __57-[UIView(AdditionalLayoutSupport) _switchToLayoutEngine:]_block_invoke + 571
    7   UIKitCore                           0x000000011959b884 -[UIView(AdditionalLayoutSupport) _switchToLayoutEngine:] + 217
    8   UIKitCore                           0x000000011959bbf3 __57-[UIView(AdditionalLayoutSupport) _switchToLayoutEngine:]_block_invoke_2 + 213
    9   Foundation                          0x000000010f7d0f46 -[NSISEngine withBehaviors:performModifications:] + 110
    10  UIKitCore                           0x000000011959baf7 __57-[UIView(AdditionalLayoutSupport) _switchToLayoutEngine:]_block_invoke + 571
    11  UIKitCore                           0x000000011959b884 -[UIView(AdditionalLayoutSupport) _switchToLayoutEngine:] + 217
    12  UIKitCore                           0x000000011964d96f __45-[UIView(Hierarchy) _postMovedFromSuperview:]_block_invoke + 112
    13  UIKitCore                           0x000000011964d875 -[UIView(Hierarchy) _postMovedFromSuperview:] + 795
    14  UIKitCore                           0x000000011965dae5 -[UIView(Internal) _addSubview:positioned:relativeTo:] + 1948
    15  Satpam Mantab                       0x000000010d8096e4 $s13Satpam_Mantab38NewsAndInformationDetailViewControllerC21viewDidLayoutSubviewsyyFyAA0cdE12CommentModelCXEfU_ + 1060
    16  Satpam Mantab                       0x000000010d80a387 $s13Satpam_Mantab38NewsAndInformationDetailViewControllerC21viewDidLayoutSubviewsyyFyAA0cdE12CommentModelCXEfU_TA + 23
    17  Satpam Mantab                       0x000000010d80a3a9 $s13Satpam_Mantab30NewsAndInformationCommentModelCs5Error_pIggzo_ACsAD_pIegnzo_TR + 25
    18  Satpam Mantab                       0x000000010d80a43b $s13Satpam_Mantab30NewsAndInformationCommentModelCs5Error_pIggzo_ACsAD_pIegnzo_TRTA + 27
    19  libswiftCore.dylib                  0x00000001116cc9e4 $sSTsE7forEachyyy7ElementQzKXEKF + 452
    20  Satpam Mantab                       0x000000010d809226 $s13Satpam_Mantab38NewsAndInformationDetailViewControllerC21viewDidLayoutSubviewsyyF + 5014
    21  Satpam Mantab                       0x000000010d80a584 $s13Satpam_Mantab38NewsAndInformationDetailViewControllerC21viewDidLayoutSubviewsyyFTo + 36
    22  UIKitCore                           0x0000000119663fe8 -[UIView(CALayerDelegate) layoutSublayersOfLayer:] + 1800
    23  QuartzCore                          0x000000010f2cad22 -[CALayer layoutSublayers] + 173
    24  QuartzCore                          0x000000010f2cf9fc _ZN2CA5Layer16layout_if_neededEPNS_11TransactionE + 396
    25  QuartzCore                          0x000000010f2dbd58 _ZN2CA5Layer28layout_and_display_if_neededEPNS_11TransactionE + 72
    26  QuartzCore                          0x000000010f24b24a _ZN2CA7Context18commit_transactionEPNS_11TransactionE + 328
    27  QuartzCore                          0x000000010f282606 _ZN2CA11Transaction6commitEv + 610
    28  UIKitCore                           0x00000001191ac99c _afterCACommitHandler + 245
    29  CoreFoundation                      0x00000001105532c7 __CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION__ + 23
    30  CoreFoundation                      0x000000011054d78e __CFRunLoopDoObservers + 430
    31  CoreFoundation                      0x000000011054de01 __CFRunLoopRun + 1505
    32  CoreFoundation                      0x000000011054d4d2 CFRunLoopRunSpecific + 626
    33  GraphicsServices                    0x000000011676d2fe GSEventRunModal + 65
    34  UIKitCore                           0x0000000119184fc2 UIApplicationMain + 140
    35  Satpam Mantab                       0x000000010d82938b main + 75
    36  libdyld.dylib                       0x0000000112b7f541 start + 1
)
libc++abi.dylib: terminating with uncaught exception of type NSException

I tried to debug the code several times, and I found that this line of code below is the one that triggers the error.

view.addConstraints([
    NSLayoutConstraint(item: view, attribute: .leading, relatedBy: .equal, toItem: self, attribute: .leading, multiplier: 1.0, constant: 0),
    ...
])

If I remove above constraints code, then the application run smoothly. The constraints it self is basically to set the view to be relative to the parent view (the owner). Without the constraints the frame of the view will be messed up. So I need it.

What should I do get rid the error? (keeping the constraints without getting any error)

Answer 1

Try to let self to add the constraints:

addConstraints([
    NSLayoutConstraint(item: view, attribute: .leading, relatedBy: .equal, toItem: self, attribute: .leading, multiplier: 1.0, constant: 0),
    NSLayoutConstraint(item: view, attribute: .trailing, relatedBy: .equal, toItem: self, attribute: .trailing, multiplier: 1.0, constant: 0),
    NSLayoutConstraint(item: view, attribute: .top, relatedBy: .equal, toItem: self, attribute: .top, multiplier: 1.0, constant: 0),
    NSLayoutConstraint(item: view, attribute: .bottom, relatedBy: .equal, toItem: self, attribute: .bottom, multiplier: 1.0, constant: 0)
    ])