A layout object that manages the layout-related attributes for a given item in a collection view.
- iOS 6.0+
- Mac Catalyst 13.0+
- tvOS 9.0+
Layout objects create instances of this class when asked to do so by the collection view. In turn, the collection view uses the layout information to position cells and supplementary views inside its bounds.
In most cases, you use this class as-is. If you want to supplement the base layout attributes with custom layout attributes, you can subclass and define whatever properties you want to store the additional layout data. Because layout attribute objects may be copied by the collection view, make sure your subclass conforms to the
NSCopying protocol by implementing any methods appropriate for copying your custom attributes to new instances of your subclass. In addition to defining your subclass, your
UICollection objects need to implement the
apply method so that they can apply any custom attributes at layout time.
If you subclass and implement any custom layout attributes, you must also override the inherited isEqual: method to compare the values of your properties. In iOS 7 and later, the collection view does not apply layout attributes if those attributes have not changed. It determines whether the attributes have changed by comparing the old and new attribute objects using the isEqual: method. Because the default implementation of this method checks only the existing properties of this class, you must implement your own version of the method to compare any additional properties. If your custom properties are all equal, call
super and return the resulting value at the end of your implementation.