It’s been a pretty exciting summer as far as Auto Layout goes. I’m busy going over material so I can get some dates and work estimates to Trina on a possible 3rd edition of Auto Layout. Between Swift, OSX, iOS 8, and whatever is going to be announced in September, it looks like a particularly interesting place to be.
I can’t tell you how thrilled I am about active, the property that self-installs and removes constraints to their natural destination. I submitted my first radar on this back before the first edition was even published. Now with the third edition, I suppose I’ll be all “Yeah, that’s my radar baby!”
The long iOS 8 summer first gave us left and right layout guides, a la the top and bottom guides we first encountered in iOS 7 but they soon disappeared and have since been replaced by a suite of Margin-based layout attributes:
NSLayoutAttributeLeftMargin NS_ENUM_AVAILABLE_IOS(8_0), NSLayoutAttributeRightMargin NS_ENUM_AVAILABLE_IOS(8_0), NSLayoutAttributeTopMargin NS_ENUM_AVAILABLE_IOS(8_0), NSLayoutAttributeBottomMargin NS_ENUM_AVAILABLE_IOS(8_0), NSLayoutAttributeLeadingMargin NS_ENUM_AVAILABLE_IOS(8_0), NSLayoutAttributeTrailingMargin NS_ENUM_AVAILABLE_IOS(8_0), NSLayoutAttributeCenterXWithinMargins NS_ENUM_AVAILABLE_IOS(8_0), NSLayoutAttributeCenterYWithinMargins NS_ENUM_AVAILABLE_IOS(8_0),
Comments and properties in the UIView header file indicate a layout tree of margins. I think it’s fair to assume this ties into the adaptive application that runs properly both on full-screen as well as side-by-side.
/* -layoutMargins returns a set of insets from the edge of the view's bounds that denote a default spacing for laying out content. If preservesSuperviewLayoutMargins is YES, margins cascade down the view tree, adjusting for geometry offsets, so that setting the left value of layoutMargins on a superview will affect the left value of layoutMargins for subviews positioned close to the left edge of their superview's bounds If your view subclass uses layoutMargins in its layout or drawing, override -layoutMarginsDidChange in order to refresh your view if the margins change. */ @property (nonatomic) UIEdgeInsets layoutMargins NS_AVAILABLE_IOS(8_0); @property (nonatomic) BOOL preservesSuperviewLayoutMargins NS_AVAILABLE_IOS(8_0); // default is NO - set to enable pass-through or cascading behavior of margins from this view’s parent to its children - (void)layoutMarginsDidChange NS_AVAILABLE_IOS(8_0);
Unfortunately, the material from WWDC is light on details and these updates didn’t take place until fairly recent betas. Got any insights into how this material will play out? I’d love to hear it. (And thanks in advance!)