Android Animation Theory

Siva Ramakrishna

Agenda❖Overview

❖Animation Systems

❖Details of each System

❖References

Overview❖Android provides variety of APIs to animate UI elements and create

custom 2D and 3D graphics.

❖The presentation details about the available techniques to create different animations using different systems provided by android.

Animation SystemsAndroid provides the following 3 different animation systems.

❖Property Animation

❖View Animation

❖Drawable Animation

Property Animation❖Introduced in Android 3.0 version.

❖Allows to animate property of any object including the one which is not visible to the user.

❖Allows to animate on custom types as well.

❖Extensible.

How it works?❖Modifies the property value of an object over a specified period of

time.

❖Property of an object is nothing but the field in an object.

❖To animate, specify the below things.

❖what property value you want to change over a time. Ex: object’s position

❖duration of the animation

❖range of values

continued...Property animation system lets you define the following things.

❖ Duration

➢ Duration of the animation.

❖ Time Interpolation

➢ How the property value should be changed over the time. Its a fn of time.

❖ Repeat Count and behavior

➢ whether to repeat the animation or not and also the behavior of the animation.

❖ Animator Sets

➢ Define a set of animations and play them in a sequence.

❖ Frame Refresh Rate

❖ Specify how often the animation should be refreshed.

example

In the above example, consider ‘x’ is the property of the object.

observe the value of ‘x’ changes over the period of 40ms.

interpolator determines the value of ‘x’ based on linear or nonlinear fn of time. Hence it plays very important role for creating any animation.

ValueAnimator

❖ValueAnimator object keeps track of your animation's timing, such as how long the animation has been running, and the current value of the property that it is animating.

ValueAnimator❖The ValueAnimator encapsulates TimeInterpolator and

TypeEvaluator.

❖TimeInterpolator which defines the interpolation of the animation. Android supports many implementations of TimeInterpolator.

➢ Ex: AccelerateInterpolator

❖TypeEvaluator which defines how to calculate the property value of the animation. Android provides many implementations TypeEvaluators.

➢ Ex: IntEvaluator

❖ValueAnimator, TimeInterpolator and TypeEvaluator work hand in hand to complete the animation.

Utility classes❖ObjectAnimator

➢ Sub class of ValueAnimator which allows to set target object and object’s property to animate.

➢ Makes the process of animating values of target objects much easier.

➢ Sometimes you may have to use ValueAnimator due some restriction on the objectAnimator where some of the property access methods are not accessible/missing.

❖ AnimatorSet➢ Animations can be grouped and played related to each other.

➢ Animations can be played sequentially, after a delay between each animation.

❖Support for animating views has been added in 3.0

❖Using ViewPropertyAnimator makes easy to animate views.

View Animation❖Can be used to perform the tweened animation on the views.

❖A tween animation can perform series of transformations(position,size,rotation and transparency) on the content of the view object. Ex: if you have a textview, you can move,rotate, shrink and grow the size.

❖Animation can be defined either in XML file or in code. XML file is more readable and reusable.

❖Animation instructions defines the transformation you want to occur, animation duration, when to occur.

❖Animation transformations can be simultaneous or sequential.

❖Interpolator is used to determine how a transformation is applied over time.

Drawable Animation❖Lets you load a series of drawable resources to create an animation.

❖Traditional style of creating an animation where series of images played like film roll.

❖AnimationDrawable is the main class to define animation through code.

❖Animation can be created using XML file as well.<animation-list xmlns:android="http://schemas.android.com/apk/res/android" android:oneshot="true"> <item android:drawable="@drawable/rocket_thrust1" android:duration="200" /> <item android:drawable="@drawable/rocket_thrust2" android:duration="200" /> <item android:drawable="@drawable/rocket_thrust3" android:duration="200" /></animation-list>

Property Animation vs View Animation❖View Animation only allows

➢ to animate view objects. Non-view objects can not animated using this system.

➢ Only few aspects of the view can be animated like size, rotation, transparency.

➢ Original object of the view will not be changed.

❖ Using Property Animation all the above limitation can be removed as it is more modular.

❖However, View Animation system takes less setup time and required less code to be written.

References and Resources❖For defining animation in an XML file. Refer

http://developer.android.com/guide/topics/resources/animation-resource.html

❖Refer API Demo Sample(animation package) for examples.

❖http://developer.android.com/guide/topics/graphics/overview.html

❖http://android-developers.blogspot.in/2011/05/introducing-viewpropertyanimator.html