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Revision as of 13:49, 27 June 2013 by Tomi_ (Talk | contribs)

Creating Simple Animations with Java ME

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This article explains how to create simple animations with Java ME. The code introduced in this article is compatible with most Java ME devices including Series 40 phones and Nokia Asha software platform 1.0.

Article Metadata
Code ExampleTested with
SDK: Nokia Asha SDK 1.0
Compatibility
Platform(s): Series 40, Nokia Asha software platfrom 1.0 and later
Nokia Asha
Nokia Asha Platform 1.0
Series 40
Article
Created: (28 Jun 2013)
Last edited: Tomi_ (27 Jun 2013)

Contents

Introduction

The standard LCDUI framework has no out-of-the-box animations. LWUIT does provide them, but in case you want to stick with the LCDUI you have no choice but to implement them yourself. Nokia UI API provides the FrameAnimator package, but that is not generic and has dependency to the user interface (UI) components. This article studies implementing a simple, generic, UI independent animation framework that is both efficient and easy to use. The full source code is available here: File:CustomCategoryBarDemo-2013-06-27.zip

Implementation

Architecture

Animation-fw-architecture.png

Easing curves

In addition to the duration and the starting and ending point, easing curves play a vital part in defining the behavior of an animation. The simplest easing curve, linear curve, moves the object you are animating from the source to the destination point with steady speed where-as in-out-quad easing curves makes the animation more vivid.

Implementation-wise the approach here is to calculate the values for the animation beforehand. The easing curve implementation is responsible for calculating the values. The abstract base class EasingCurve implements everything but the calculate() method. The calculate() method of the linear easing curve is as follows:

public class LinearEasingCurve extends EasingCurve {
public boolean calculate(int from, int to, int duration) {
_duration = duration;
_steps = _duration / IntAnimation.UPDATE_INTERVAL;
_values = new int[_steps];
_currentStepIndex = 0;
final int stepLength = (to - from) / (_steps - 1);
 
_values[0] = from;
_values[_steps - 1] = to;
 
for (int i = 1; i < _steps - 1; ++i) {
_values[i] = from + stepLength * i;
}
 
return true;
}
}

Currently, this light animation framework implements three easing curves: linear, in-out-quad and out-in-quad.

Usage

Using the animation package is easy. First have your class, that handles the animating, derive from AnimationListener. Create the IntAnimation instance where convenient - straightforward place to do it is in the constructor. Remember to set the listener so that you can receive the animated values and changes in the animation states.

public class MyCanvas
extends Canvas
implements AnimationListener
{
// Constants
...
private static final int ANIMATION_DURATION = 500;
private static final int EASING_CURVE = IntAnimation.EASING_CURVE_INOUTQUAD;
 
// Members
...
private IntAnimation _animation = null;
...
 
/**
* Constructor.
*/

public MyCanvas() {
super();
...
_animation = new IntAnimation();
_animation.setListener(this);
...

Implement the methods required by the AnimationListener interface:

    /**
* @see AnimationListener#onAnimatedValueChanged(int)
*/

public void onAnimatedValueChanged(int value) {
// Handle the value
...
repaint();
}
 
/**
* @see AnimationListener#onAnimationStateChanged(int)
*/

public void onAnimationStateChanged(int state) {
switch (state) {
case IntAnimation.STATE_RUNNING:
...
break;
case IntAnimation.STATE_STOPPED:
...
break;
case IntAnimation.STATE_FINISHED:
...
break;
default:
break;
}
}

Then just let it rip:

boolean started = _animation.start(from, to, ANIMATION_DURATION, EASING_CURVE))
 
if (!started) {
// Failed to start the animation! Handle this situation gracefully - maybe by just jumping to the "to" point.
}

Summary

It's not hard to do animations with Java ME. However, it requires work and when you decide to implement the animations, make sure you do it in a way that you can re-use your stuff later in your other projects. The study, explained in this article, produced an animation package that is quite generic and you are free to use it and expand it with your own easing curves. Further improvements to this package would include implementing a dedicated thread for animations. The current implementation is basically based on just fire-and-forget principle.

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