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How to identify your Auto Layout constraints

Swift version: 5.1

Paul Hudson    @twostraws   

Auto Layout constraints a powerful way of expressing your layouts, but when they go wrong they can be hard to debug. Fortunately, all constraints have a built-in identifier property that you can use to identify them uniquely.

It’s an optional string so you don’t have to provide anything, but if you do set an identifier you’ll find it much easier to see where your constraints are going wrong because Xcode will use those identifiers in its debug logs.

If you create your constraints in code, just set the identifier property to a string as you go – “Main Title Horizontal Center” for example. If you use Interface Builder, you can select any constraint and you’ll see a dedicated “Identifier” text property you can fill in.

There is literally no reason not to add identifiers to your constraints – they don’t affect your layouts at all, but they do make layout debugging significantly easier!

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Available from iOS 7.0

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