LayoutTransition Class

Definition

[Android.Runtime.Register("android/animation/LayoutTransition", DoNotGenerateAcw=true)]
public class LayoutTransition : Java.Lang.Object

[<Android.Runtime.Register("android/animation/LayoutTransition", DoNotGenerateAcw=true)>]
type LayoutTransition = class
    inherit Object

Inheritance

Object

Object

LayoutTransition

Attributes

RegisterAttribute

Remarks

This class enables automatic animations on layout changes in ViewGroup objects. To enable transitions for a layout container, create a LayoutTransition object and set it on any ViewGroup by calling ViewGroup#setLayoutTransition(LayoutTransition). This will cause default animations to run whenever items are added to or removed from that container. To specify custom animations, use the LayoutTransition#setAnimator(int, Animator) setAnimator() method.

One of the core concepts of these transition animations is that there are two types of changes that cause the transition and four different animations that run because of those changes. The changes that trigger the transition are items being added to a container (referred to as an "appearing" transition) or removed from a container (also known as "disappearing"). Setting the visibility of views (between GONE and VISIBLE) will trigger the same add/remove logic. The animations that run due to those events are one that animates items being added, one that animates items being removed, and two that animate the other items in the container that change due to the add/remove occurrence. Users of the transition may want different animations for the changing items depending on whether they are changing due to an appearing or disappearing event, so there is one animation for each of these variations of the changing event. Most of the API of this class is concerned with setting up the basic properties of the animations used in these four situations, or with setting up custom animations for any or all of the four.

By default, the DISAPPEARING animation begins immediately, as does the CHANGE_APPEARING animation. The other animations begin after a delay that is set to the default duration of the animations. This behavior facilitates a sequence of animations in transitions as follows: when an item is being added to a layout, the other children of that container will move first (thus creating space for the new item), then the appearing animation will run to animate the item being added. Conversely, when an item is removed from a container, the animation to remove it will run first, then the animations of the other children in the layout will run (closing the gap created in the layout when the item was removed). If this default choreography behavior is not desired, the #setDuration(int, long) and #setStartDelay(int, long) of any or all of the animations can be changed as appropriate. Keep in mind, however, that if you start an APPEARING animation before a DISAPPEARING animation is completed, the DISAPPEARING animation stops, and any effects from the DISAPPEARING animation are reverted. If you instead start a DISAPPEARING animation before an APPEARING animation is completed, a similar set of effects occurs for the APPEARING animation.

The animations specified for the transition, both the defaults and any custom animations set on the transition object, are templates only. That is, these animations exist to hold the basic animation properties, such as the duration, start delay, and properties being animated. But the actual target object, as well as the start and end values for those properties, are set automatically in the process of setting up the transition each time it runs. Each of the animations is cloned from the original copy and the clone is then populated with the dynamic values of the target being animated (such as one of the items in a layout container that is moving as a result of the layout event) as well as the values that are changing (such as the position and size of that object). The actual values that are pushed to each animation depends on what properties are specified for the animation. For example, the default CHANGE_APPEARING animation animates the left, top, right, bottom, scrollX, and scrollY properties. Values for these properties are updated with the pre- and post-layout values when the transition begins. Custom animations will be similarly populated with the target and values being animated, assuming they use ObjectAnimator objects with property names that are known on the target object.

This class, and the associated XML flag for containers, animateLayoutChanges="true", provides a simple utility meant for automating changes in straightforward situations. Using LayoutTransition at multiple levels of a nested view hierarchy may not work due to the interrelationship of the various levels of layout. Also, a container that is being scrolled at the same time as items are being added or removed is probably not a good candidate for this utility, because the before/after locations calculated by LayoutTransition may not match the actual locations when the animations finish due to the container being scrolled as the animations are running. You can work around that particular issue by disabling the 'changing' animations by setting the CHANGE_APPEARING and CHANGE_DISAPPEARING animations to null, and setting the startDelay of the other animations appropriately.

Java documentation for android.animation.LayoutTransition.

Portions of this page are modifications based on work created and shared by the Android Open Source Project and used according to terms described in the Creative Commons 2.5 Attribution License.

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Applies to