Adding constraint crash down the application

Question

I have a custom UIView for designing UITableViewCell, every things work perfect only it's not get resize properly. And when I am trying to add the constraint it crashed. I used the below code.

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {

    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:@"identifier"];
    if(!cell) {
        cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:@"identifier"];
        UIView *vBackView = [[UIView alloc] initWithFrame:aFrame];
        [[cell contentView] addSubview:vBackView];

        [vBackView addConstraint:[NSLayoutConstraint constraintWithItem:[cell contentView]
                                                              attribute:NSLayoutAttributeTop
                                                              relatedBy:NSLayoutRelationEqual
                                                                 toItem:vBackView
                                                              attribute:NSLayoutAttributeTop
                                                             multiplier:1.0
                                                               constant:0.0]];

        [vBackView addConstraint:[NSLayoutConstraint constraintWithItem:[cell contentView]
                                                              attribute:NSLayoutAttributeLeading
                                                              relatedBy:NSLayoutRelationEqual
                                                                 toItem:vBackView
                                                              attribute:NSLayoutAttributeLeading
                                                             multiplier:1.0
                                                               constant:0.0]];

        [vBackView addConstraint:[NSLayoutConstraint constraintWithItem:[cell contentView]
                                                              attribute:NSLayoutAttributeBottom
                                                              relatedBy:NSLayoutRelationEqual
                                                                 toItem:vBackView
                                                              attribute:NSLayoutAttributeBottom
                                                             multiplier:1.0
                                                               constant:0.0]];

        [vBackView addConstraint:[NSLayoutConstraint constraintWithItem:[cell contentView]
                                                              attribute:NSLayoutAttributeTrailing
                                                              relatedBy:NSLayoutRelationEqual
                                                                 toItem:vBackView
                                                              attribute:NSLayoutAttributeTrailing
                                                             multiplier:1.0
                                                               constant:0.0]];
    }

    // Doing other stuff

    return cell;
}

And in log it's shows

2015-06-13 12:51:57.482 DigitalBoard[5314:70921] The view hierarchy is not prepared for the constraint: <NSLayoutConstraint:0x7fb508dc0ae0 UITableViewCell:0x7fb508dbb0a0'cellIdentifier'.top == UIView:0x7fb508dc16f0.top>
    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 _viewHierarchyUnpreparedForConstraint:] to debug.

2015-06-13 12:51:57.485 DigitalBoard[5314:70921] View hierarchy unprepared for constraint.
    Constraint: <NSLayoutConstraint:0x7fb508dc0ae0 UITableViewCell:0x7fb508dbb0a0'cellIdentifier'.top == UIView:0x7fb508dc16f0.top>
    Container hierarchy: 
<UIView: 0x7fb508dc16f0; frame = (0 0; 400 44); autoresize = RM+BM; tag = 1; layer = <CALayer: 0x7fb508dc0720>>
   | <UILabel: 0x7fb508dc5310; frame = (15 0; 105 44); text = 'Meeting #'; opaque = NO; autoresize = RM+BM; userInteractionEnabled = NO; tag = 2; layer = <_UILabelLayer: 0x7fb508dc54c0>>
   | <UIButton: 0x7fb508dc5880; frame = (130 7; 80 30); opaque = NO; autoresize = RM+BM; tag = 3; layer = <CALayer: 0x7fb508da95d0>>
   | <UIButton: 0x7fb508dc5fa0; frame = (220 7; 80 30); opaque = NO; autoresize = RM+BM; tag = 4; layer = <CALayer: 0x7fb508dc5c60>>
   | <UIButton: 0x7fb508dc61c0; frame = (310 7; 80 30); opaque = NO; autoresize = RM+BM; tag = 5; layer = <CALayer: 0x7fb508dc5e90>>
   | <UIImageView: 0x7fb508dc6540; frame = (0 42; 400 2); autoresize = RM+BM; userInteractionEnabled = NO; layer = <CALayer: 0x7fb508dc6680>>
    View not found in container hierarchy: <UITableViewCell: 0x7fb508dbb0a0; frame = (0 0; 320 44); layer = <CALayer: 0x7fb508da98e0>>
    That view's superview: NO SUPERVIEW

2015-06-13 12:51:57.498 DigitalBoard[5314:70921] *** 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:0x7fb508dc0ae0 UITableViewCell:0x7fb508dbb0a0'cellIdentifier'.top == UIView:0x7fb508dc16f0.top> view:<UIView: 0x7fb508dc16f0; frame = (0 0; 400 44); autoresize = RM+BM; tag = 1; layer = <CALayer: 0x7fb508dc0720>>'
*** First throw call stack:
(
etc....

Can anyone help to understand what exactly the problem is.

Possible duplicate with this question : http://stackoverflow.com/questions/18177262/centering-subviews-x-in-autolayout-throws-not-prepared-for-the-constraint — MGY, Jun 13 '15 at 08:10
@gyer no it's not duplicate. because I have tried those solution but not working... this constraint are being added under `cellForRowAtIndexPath` — Tapas Pal, Jun 13 '15 at 09:10

johnpatrickmorgan · Answer 1 · 2015-06-13T09:39:55.303

0

You shouldn't add your constraints to vBackView. I assume vBackView is a subview of cell.contentView in which case you should be adding the constraints to the cell.contentView instead.

The crash log tells you why:

When added to a view, the constraint's items must be descendants of that view (or the view itself).

Change each line of code to begin: [cell.contentView addConstraint:....

edited Jun 13 '15 at 09:39

answered Jun 13 '15 at 09:34

johnpatrickmorgan

2,372
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17

Please show your code where you add `vBackView` as a subview, so we can get an idea of your view hierarchy. – johnpatrickmorgan Jun 15 '15 at 09:27

Adding constraint crash down the application

1 Answers1