A trait collection describes the iOS interface environment for your app, including traits such as horizontal and vertical size class, display scale, and user interface idiom. To create an adaptive interface, write code to adjust your app’s layout according to changes in these traits.
- iOS 8.0+
- tvOS 9.0+
The iOS trait environment is exposed though the
trait property of the
UITrait protocol. This protocol is adopted by the following classes:
UIView. You access specific trait values using the
user properties. The values that express idiom and size traits are defined in the
UIUser enumerations; the value for the display scale trait is expressed as a floating point number.
To make your view controllers and views responsive to changes in the iOS interface environment, override the
trait method from the trait environment protocol. To customize view controller animations in response to interface environment changes, override the
will method of the
This figure shows the horizontal (width) and vertical (height) size classes your app can encounter when running on various devices fullscreen.
You can create standalone trait collections to assist in matching against specific environments. The
UITrait class includes four specialized constructors as well as a constructor that lets you combine an array of trait collections,
One important use of standalone trait collections is to enable conditional use of images based on the current iOS interface environment. You can associate a trait collection with a
UIImage instance by way of a
UIImage instance, as described in the overview section of
UIImage. For information on configuring asset catalogs graphically from within the Xcode IDE, see Asset Catalog Help.
You can employ a standalone trait collection to enable a two-column split view in landscape orientation on iPhone. See the
set method of the
For the WWDC 2014 presentation on creating adaptive interfaces in iOS, see Building Adaptive Apps with UIKit.
3D Touch and Trait Collections
Starting in iOS 9, you can use this class to check whether the device on which your app is running supports 3D Touch. Read the value of the
force property on the trait collection for any object in your app with a trait environment. For information about trait environments, see
UITrait. For the possible values of the force touch capability property, see the
Because a user can turn off 3D Touch in Settings, check the value of the
force property in your implementation of the
trait method, and adjust your code paths according to the property’s value.