Jafar Jafar - 3 months ago 46
iOS Question

Auto layout constraints issue on iOS7 in UITableViewCell

I'm using auto layout constraints programmatically to layout my custom UITableView cells and I'm correctly defining the cell sizes in

tableView:heightForRowAtIndexPath:


It's working just fine on iOS6 and it does look fine in iOS7 as well

BUT when I run the app on iOS7, here's the kind of message I see in the console:

Break on objc_exception_throw to catch this in the debugger.
The methods in the UIConstraintBasedLayoutDebugging category on UIView listed in <UIKit/UIView.h> may also be helpful.
2013-10-02 09:56:44.847 Vente-Exclusive[76306:a0b] Unable to simultaneously satisfy constraints.
Probably at least one of the constraints in the following list is one you don't want. Try this: (1) look at each constraint and try to figure out which you don't expect; (2) find the code that added the unwanted constraint or constraints and fix it. (Note: If you're seeing NSAutoresizingMaskLayoutConstraints that you don't understand, refer to the documentation for the UIView property translatesAutoresizingMaskIntoConstraints)
(
"<NSLayoutConstraint:0xac4c5f0 V:|-(15)-[UIImageView:0xac47f50] (Names: '|':UITableViewCellContentView:0xd93e850 )>",
"<NSLayoutConstraint:0xac43620 V:[UIImageView:0xac47f50(62)]>",
"<NSLayoutConstraint:0xac43650 V:[UIImageView:0xac47f50]-(>=0)-[UIView:0xac4d0f0]>",
"<NSLayoutConstraint:0xac43680 V:[UIView:0xac4d0f0(1)]>",
"<NSLayoutConstraint:0xac436b0 V:[UIView:0xac4d0f0]-(0)-| (Names: '|':UITableViewCellContentView:0xd93e850 )>",
"<NSAutoresizingMaskLayoutConstraint:0xac6b120 h=--& v=--& V:[UITableViewCellContentView:0xd93e850(44)]>"
)

Will attempt to recover by breaking constraint
<NSLayoutConstraint:0xac43650 V:[UIImageView:0xac47f50]-(>=0)-[UIView:0xac4d0f0]>


And indeed there's one of the constraint in that list I don't want :

"<NSAutoresizingMaskLayoutConstraint:0xac6b120 h=--& v=--& V:[UITableViewCellContentView:0xd93e850(44)]>"


and I cannot set the
translatesAutoresizingMaskIntoConstraints
property of the
contentView
to NO => it would mess up the entire cell.

44 is the default cell height but I defined my custom heights in the table view delegate so why does the cell contentView has this constraint? What could cause this?

In iOS6 it's not happening and everything looks just fine on both iOS6 and iOS7.

My code is quite big so I won't post it here but feel free to ask for a pastebin if you need it.

To specify how I'm doing it, on cell intialization:


  • I create all my labels, buttons, etc

  • I set their
    translatesAutoresizingMaskIntoConstraints
    property to NO

  • I add them as subviews of the
    contentView
    of the cell

  • I add the constraints on the
    contentView



I'm also deeply interested in understanding why this happens only on iOS7.

Answer

I had this problem as well.. It appears that the contentView's frame doesn't get updated until layoutSubviews is called however the frame of the cell is updated earlier leaving the contentView's frame set to {0, 0, 320, 44} at the time when the constraints are evaluated.

After looking at the contentView in more detail, It appears that autoresizingMasks are no longer being set.

Setting the autoresizingMask before you constrain your views can resolve this issue:

- (id)initWithStyle:(UITableViewCellStyle)style reuseIdentifier:(NSString *)reuseIdentifier
{
    self = [super initWithStyle:UITableViewCellStyleDefault reuseIdentifier:reuseIdentifier];
    if (self)
    {
        self.contentView.autoresizingMask = UIViewAutoresizingFlexibleHeight|UIViewAutoresizingFlexibleWidth;
        [self loadViews];
        [self constrainViews];
    }
    return self;
}