What Old Is New Again in Auto Layout on iOS 10

The “What’s New in Auto Layout” talk seems to be becoming an annual tradition at WWDC. I didn’t attend in person this year, because I couldn’t get out of San Francisco fast enough on the Friday of the conference, but I recently sat down and watched the video and have been thinking about what Apple is offering this year.

This year’s session was surprising, to say the least. After spending the last three years preaching that autoresizing masks weren’t long for this world, Apple went ahead and made me eat a full serving of crow by “introducing” a new feature in Xcode 8 called “autoresizing masks.” For those new to Mac and iOS development, autoresizing masks is the “old” way of doing things before Auto Layout was introduced back with OS X Lion. Instead of explicitly setting relationships between your views, you set the springs and struts values to assign the resizing and pinning behavior of the view.

Even with Auto Layout, springs and struts never really went away. When the system unable to determine the layout of your application with your given set of constraints, it would plug in its own set of constraints implicitly, usually tied to springs and struts, to fill in the gaps. Any time you call translatesAutoresizingMaskIntoConstraints on a UIView you are opting out of letting the system create constraints for you based off autoresizing masks as well.

With the new incremental adoption policies in iOS 10 and above, Apple is now stepping back its hardline on Auto Layout adoption and instead realizing that in some scenarios, the old way can actually can be better. Specifically, if you just need to set up some basic resizing behavior opting into letting the system add its default constraints at compile time with a little help from your defined autoresizing masks is less work than manually creating constraints yourself. In a lot of ways it feels like a more pragmatic middle ground between the old way of doing things and the 100% pure Auto Layout approach.

Resizing masks are still not without their tradeoffs: if you are dealing with localization you’re going to want to opt into Auto Layout and all that is has to offer. I just localized an entire app and it would have been far more hellacious if I was sticking to autoresizing masks instead of Auto Layout. But, for things like fast prototypes or the most basic of views with minimal behavior requirements not having to set up constraints could definitely save you some development time.

By Justin Williams

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