Parallax

public abstract class Parallax
extends Object

java.lang.Object
   ↳ androidx.leanback.widget.Parallax<PropertyT extends android.util.Property>


Parallax tracks a list of dynamic Propertys typically representing foreground UI element positions on screen. Parallax keeps a list of ParallaxEffect objects which define rules to mapping property values to ParallaxTarget.

Example: // when Property "var1" changes from 15 to max value, perform parallax effect to // change myView's translationY from 0 to 100. Parallax parallax = new Parallax() {...}; p1 = parallax.addProperty("var1"); parallax.addEffect(p1.at(15), p1.atMax()) .target(myView, PropertyValuesHolder.ofFloat("translationY", 0, 100));

To create a ParallaxEffect, user calls addEffect(PropertyMarkerValue[]) with a list of Parallax.PropertyMarkerValue which defines the range of Parallax.IntProperty or Parallax.FloatProperty. Then user adds ParallaxTarget into ParallaxEffect.

App may subclass Parallax.IntProperty or Parallax.FloatProperty to supply additional information about how to retrieve Property value. RecyclerViewParallax is a great example of Parallax implementation tracking child view positions on screen.

Restrictions of properties

  • FloatProperty and IntProperty cannot be mixed in one Parallax
  • Values must be in ascending order.
  • If the UI element is unknown above screen, use UNKNOWN_BEFORE.
  • if the UI element is unknown below screen, use UNKNOWN_AFTER.
  • UNKNOWN_BEFORE and UNKNOWN_AFTER are not allowed to be next to each other.
These rules will be verified at runtime.

Subclass must override updateValues() to update property values and perform ParallaxEffects. Subclass may call updateValues() automatically e.g. RecyclerViewParallax calls updateValues() in RecyclerView scrolling. App might call updateValues() manually when Parallax is unaware of the value change. For example, when a slide transition is running, RecyclerViewParallax is unaware of translation value changes; it's the app's responsibility to call updateValues() in every frame of animation.

Summary

Nested classes

class Parallax.FloatProperty

FloatProperty provide access to an index based integer type property inside Parallax

class Parallax.IntProperty