Android custom Animation for an ArcShape


First let me explain my goal. I am trying to make an Animation that changes the properties of an ArcShape. An ArcShape's constructor takes two fields: startAngle and sweepAngle. I want to animate the sweepAngle so that it appears on screen as a continuously shrinking circle.

You can picture this animation by imagining PacMan. Imagine his mouth is closed. This animation would be akin to him opening his upper jaw more and more until there was no more PacMan.

Now... I have a couple of issues with implementing this. First, once an ArcShape is created, there are no built in methods of changing it's sweepAngle. This brings me to my first question: Is there any way to override ArcShape and implement some setSweepAngle method? Or will I have to create a new ArcShape for each sweepAngle I wish to display?

Now on to the second issue... Assuming I found a solution to the first issue, how could I create this Animation? This is the gist of what I have now:

public class OpenPacman extends Animation {
  public OpenPacman(float startAngle, float sweepAngle) {
    mStartAngle = startAngle;
    mSweepAngle = sweepAngle;

  protected void applyTransformation(float interpolatedTime, Transformation t) {
    /* This represents the current sweepAngle */
    float currAngle = mStartAngle + ((mSweepAngle - mStartAngle) * interpolatedTime);

    //Now I need to update the ArcShape's sweepAngle to currAngle. But HOW?
By : dfetter88


I think you might be better off extending Drawable and override the draw() function to modify the sweep angle on each call and draw the corresponding arc. Draw is typically called every time the object is updated, which will mean that you'll have to make a new ArcShape every time it's drawn Animation is more for performing transformations on Views and other UI components.

Something like:

public class OpenPacman  

public OpenPacman(float startAngle, float sweepAngle) {  
    this.mStartAngle = startAngle;  
    this.mSweepAngle = sweepAngle;  
    this.wakaWaka = new ArcShape(this.startAngle, this.mSweepAngle);  

public void draw(Canvas c){  
  //Do drawing stuff here with the canvas

//Your other functions for calculating angle, etc and making the ArcShape changes
//Can call these from inside draw function so that when the view that contains your
//object calls draw, it updates correctly.

public float mStartAngle;  
public float msweepAngle;  
private ArcShape wakaWaka;  

Hope this gets you on the right track.

This video can help you solving your question :)
By: admin