调试时“无法同时满足约束条件”

Question

Below is the error message I receive in the debug area. It runs fine and nothing is wrong except that I receive this error. Would this prevent apple accepting the app? How do I fix it?

( "<NSLayoutConstraint:0x7f9bdaf58890 UIView:0x7f9bdaf484e0.leading == UIView:0x7f9bdaf56e30.leadingMargin + 34>", "<NSLayoutConstraint:0x7f9bdaf58930 UIView:0x7f9bdaf56e30.trailingMargin == UIView:0x7f9bdaf484e0.trailing + 34>", "<NSLayoutConstraint:0x7f9bdaf58980 H:[UIView:0x7f9bdaf484e0(300)]>", "<NSLayoutConstraint:0x7f9bdaf5bfc0 'UIView-Encapsulated-Layout-Width' H:[UIView:0x7f9bdaf56e30(375)]>" ) Will attempt to recover by breaking constraint <NSLayoutConstraint:0x7f9bdaf58980 H:[UIView:0x7f9bdaf484e0(300)]>

Answer 1

I guess this happens in a UITableView on an iPhone 6.

Since cells reach from the left edge of the tableView to the right edge the cells need to be 375 points wide. The UITableView adds the UIView-Encapsulated-Layout-Width constraint to achieve this.

The constraints you added yourself |-34-[centerView(=300)]-34-| will create a cell width of 368 points.

Since 368 != 375 this won't work.

You have a couple of options.

1. Turn your constraints into in-equal constraints, ie make the width of the centered view "greater than or equal". In code that would look like this: |-34-[centerView(>=300)]-34-|
2. Constrain your centerView with a "horizontal center in container" constraint, keep the width constraint and get rid of the edge-distance constraints.
3. Get rid of the width constraint completely. The width will change depending on the cell width. eg |-34-[centerView]-34-| , this will lead to a 307 pt wide view on iPhone 6, on iPhone 6s it will be 346 points wide and on iPhone 5 it'll be 252 points wide.

As you said the app works if the systems breaks the width=300 constraint, so you can just delete that constraint yourself. If it works without that constraint there is no point in having it.

Having two edge-distance constraints AND a width constraints at the same time doesn't make sense and defeats the purpose of auto layout.