Android: Animate Custom Drawable Programmatically
I have a custom class extending Drawable as shown below which is for drawing Arc. From my MainActivity controlling Drawable, I redraw it based on some input values, which I translated into the appropriate "corner" for the shape. For example.
This is the initial state of the drawable:
This is the second state: The 
red arrow indicates the movement I am trying to achieve
I'm trying to "animate" a change from state 1 to state 2 with wide motion. Any ideas on how to do this? Should I redraw the shape several times, gradually transitioning between states one and two?
My Drawable Code:
public class CircleLoadingBar extends Drawable implements Drawable.Callback{
private Paint paint;
private Canvas canvas;
private float angle;
private RectF outterCircle;
private float padding=30;
public void invalidateDrawable(Drawable drawable){
final Callback callback = getCallback();
if (callback != null) {
callback.invalidateDrawable(this);
}
}
public void scheduleDrawable(Drawable drawable, Runnable runnable, long l){
invalidateDrawable(drawable);
}
public void unscheduleDrawable(Drawable drawable,Runnable runnable){
//empty
}
public CircleLoadingBar(){
this(0);
}
public CircleLoadingBar( int angle){
this.angle=angle;
this.canvas=new Canvas();
paint=new Paint();
paint.setColor(Color.GREEN);
paint.setStrokeWidth(padding);
paint.setAntiAlias(true);
paint.setStrokeCap(Paint.Cap.ROUND);
paint.setStyle(Paint.Style.STROKE);
outterCircle = new RectF();
}
public void setAngle(float angle){
this.angle=angle;
}
@Override
public void draw(Canvas canvas){
canvas.save();
Rect bounds = getBounds();
outterCircle.set(bounds.left+padding,bounds.top+padding,bounds.right-padding,bounds.bottom-padding);
int[] colors = {Color.RED, Color.GREEN, Color.RED};
float[] positions = {0,0.2f,1.3f};
SweepGradient gradient3 = new SweepGradient(innerCircle.centerX(), innerCircle.centerY(),colors,positions);
paint.setShader(gradient3);
canvas.drawArc(outterCircle,90,angle,true,paint);
}
@Override
public void setAlpha(int alpha) {
// Has no effect
}
@Override
public void setColorFilter(ColorFilter cf) {
// Has no effect
}
@Override
public int getOpacity() {
// Not Implemented
return 0;
}
}
My MainActivity Code:
public class MainActivity {
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate();
setContentView(R.layout.main);
textView= (TextView) findViewById(R.id.textview);
circleLoadingBar= new CircleLoadingBar(10);
textView.setBackgroundDrawable(circleLoadingBar);
}
public void stateUpdate(float angle) {
circleLoadingBar.setAngle(angle);
textView.invalidate();
}
}
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After searching a lot, I found the answer.
Summary: I needed the Custom Drawable class to implement the Drawable.Callback and Runnable interfaces (see code below).
CustomDrawable.class
public class CustomDrawable extends Drawable implements Drawable.Callback, Runnable{
private Paint paint;
private Canvas canvas;
private int angle;
private RectF circle;
private float cx,cy;
private float mHeight,mWidth=100;
private float mRadius=20;
private Drawable.Callback cb;
private boolean running=false;
public void invalidateDrawable(Drawable drawable){
super.invalidateSelf(); //This was done for my specific example. I wouldn't use it otherwise
}
public void scheduleDrawable(Drawable drawable, Runnable runnable, long l){
invalidateDrawable(drawable);
}
public void unscheduleDrawable(Drawable drawable,Runnable runnable){
super.unscheduleSelf(runnable);
}
public CircleLoadingBar(){
this(0);
}
public CircleLoadingBar(int angle){
this.angle=angle;
paint=new Paint();
paint.setColor(Color.GREEN);
paint.setAntiAlias(true);
paint.setStrokeCap(Paint.Cap.ROUND);
paint.setStyle(Paint.Style.STROKE);
circle= new RectF();
}
@Override
public void draw(Canvas canvas){
canvas.save();
Rect bounds = getBounds();
circle.set(bounds);
canvas.drawArc(circle, 90, angle, true, paint);
}
public void nextFrame(){
unscheduleSelf(this);
scheduleSelf(this, SystemClock.uptimeMillis() + 250);
}
public void stop(){
running=false;
unscheduleSelf(this);
}
public void start(){
if(!running){
running=true;
nextFrame();
}
}
public void run(){
angle++;
invalidate();
nextFrame();
}
@Override
public void setAlpha(int alpha) {
// Has no effect
}
@Override
public void setColorFilter(ColorFilter cf) {
// Has no effect
}
@Override
public int getOpacity() {
// Not Implemented
return 0;
}
}
Now that your Drawable implements both, you can simply "start" it as a separate thread, initiated and controlled by your activity using start and stop functions.
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