Drawables Moving Example

package viewmotionexample.ballanimation;

import android.app.Activity;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Rect;
import android.graphics.drawable.Drawable;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;

import java.util.ArrayList;
import java.util.Random;


/**
 * Created by David Olsen, 2015
 * Public Domain. Use for anything.
 */

public class CirclesView extends View {
    Random random = new Random();
    ArrayList<BallDrawing> circles = new ArrayList<>();
    Activity activity;
    Paint backgroundPaint = new Paint();

    public CirclesView(Context context) {
        super(context);
        this.activity = (Activity) context;
        init();
    }

    public CirclesView(Context context, AttributeSet attrs) {
        super(context, attrs);
        this.activity = (Activity) context;
        init();
    }

    public CirclesView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        this.activity = (Activity) context;
        init();
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        int action = event.getAction();
        if (action == MotionEvent.ACTION_UP) {
            circles.add(new BallDrawing(event.getX(),event.getY()));
        }
        return true;
    }

    Drawable drawable;
    Rect drawableBounds = null;

    private void init() {
        backgroundPaint.setColor(Color.BLUE);
        drawable = getResources().getDrawable(R.drawable.bal);
        if (drawable != null) {
            drawable.setBounds(0,0,40,40);
            drawableBounds = drawable.getBounds();
        }
        Thread t = new Thread(new Runnable() {
            @Override
            public void run() {

                while (true) {
                    try {
                        Thread.sleep(100);
                        tick();

                    } catch (InterruptedException e) {
                        return;
                    }
                }
            }
        });
        t.start();
    }

    public void tick() {
        activity.runOnUiThread(new Runnable() {
            @Override
            public void run() {
                for (BallDrawing circle : circles) {
                    circle.translate(random.nextInt(10) - 5, random.nextInt(10) - 5);
                }
            }
        });

    }


    @Override
    protected void onDraw(Canvas canvas) {
        for (BallDrawing c : circles) {
            c.draw(canvas);
        }
    }

    private class BallDrawing {
        public float cx, cy;

        public BallDrawing(float cx, float cy) {
            this.cx = cx;
            this.cy = cy;
        }

        public void translate(int dx, int dy) {
            invalidate((int)cx + drawableBounds.left,(int)cy + drawableBounds.top, (int)cx+1 + drawableBounds.right, (int)cy+1 + drawableBounds.bottom);
            cx += dx;
            cy += dy;
            invalidate((int)cx + drawableBounds.left,(int)cy + drawableBounds.top, (int)cx + 1 + drawableBounds.right, (int)cy+1 + drawableBounds.bottom);
        }


        public void draw(Canvas canvas) {
            canvas.save();
            canvas.translate(cx,cy);
            drawable.draw(canvas);
            canvas.restore();
        }
    }

}