Question

This class use to draw ball but its onDraw() function not call so ball not draw

package com.bounce.app;

import org.jbox2d.collision.AABB;
import org.jbox2d.collision.shapes.CircleDef;
import org.jbox2d.collision.shapes.PolygonDef;
import org.jbox2d.common.Vec2;
import org.jbox2d.dynamics.Body;
import org.jbox2d.dynamics.BodyDef;
import org.jbox2d.dynamics.World;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Paint.Style;
import android.util.Log;
import android.view.MotionEvent;
import android.view.SurfaceHolder;
import android.view.SurfaceView;

 public class PhysicsWorld extends SurfaceView implements SurfaceHolder.Callback {

private AABB worldAABB;
private World world;

private PolygonDef groundShapeDef; 
public int W_width, W_height;
private static final String TAG = PhysicsWorld.class.getSimpleName();
protected static final int GUIUPDATEIDENTIFIER = 0x231;
public int targetFPS = 40;
public float timeStep = (10.0f/targetFPS);
public int iterations = 5; 
private int count=0;
private Body[] theBodies ;
private Paint paint;
private float radius = 10;


public PhysicsWorld(Context context, int width, int height) {
    super(context);
    getHolder().addCallback(this);
    W_width = width;
    W_height = height;
    worldAABB = new AABB();
    Vec2 min = new Vec2(-50, -50);
    Vec2 max = new Vec2(W_width+50, W_height+50);
    worldAABB.lowerBound.set(min);
    worldAABB.upperBound.set(max); 
    Vec2 gravity = new Vec2((float) 0.0, (float) -9.8);
    boolean doSleep = true;
    world = new World(worldAABB, gravity, doSleep); 

    BodyDef groundBodyDef = new BodyDef();
    groundBodyDef.position.set(new Vec2((float) 0.0, (float) -10.0));
    Body groundBody = world.createBody(groundBodyDef);
    groundShapeDef = new PolygonDef();
    groundShapeDef.setAsBox(W_width, 10);
    groundBody.createShape(groundShapeDef);

 // up :
    groundBodyDef = new BodyDef();
    groundBodyDef.position.set(new Vec2((float) 0.0, (float) (W_height + 10.0)));
    groundBody = world.createBody(groundBodyDef);
    groundShapeDef = new PolygonDef();
    groundShapeDef.setAsBox(W_width, 10);
    groundBody.createShape(groundShapeDef);

    // left :
    groundBodyDef = new BodyDef();
    groundBodyDef.position.set(new Vec2(-10, (float) 0.0));
    groundBody = world.createBody(groundBodyDef);
    groundShapeDef = new PolygonDef();
    groundShapeDef.setAsBox(10, W_height);
    groundBody.createShape(groundShapeDef);

    // right :
    groundBodyDef = new BodyDef();
    groundBodyDef.position.set(new Vec2((float) W_width + 10, (float) 0.0));
    groundBody = world.createBody(groundBodyDef);
    groundShapeDef = new PolygonDef();
    groundShapeDef.setAsBox(10, W_height);
    groundBody.createShape(groundShapeDef);

    theBodies = new Body[50];
    paint = new Paint();
    paint.setStyle(Style.FILL);
    paint.setColor(Color.RED);

}

        public void addBall(int x, int y) {
            // Create Dynamic Body
            BodyDef bodyDef = new BodyDef();
            bodyDef.position.set(x, y);
            Log.d(TAG,"Ball Created At: " + Integer.toString(x) + "," + Integer.toString(y));
            theBodies[count] = world.createBody(bodyDef);

            // Create Shape with Properties
            CircleDef circle = new CircleDef();
            circle.radius = radius;
            circle.density = (float) 1.0; 
            circle.restitution = 0.5f;
            theBodies[count].createShape(circle);
            theBodies[count].setMassFromShapes();
                 count+=1;

        } 

        public void update() {

             world.step(timeStep, iterations);

             postInvalidate();

                 }



    @Override
    protected void onDraw(Canvas canvas) {
         Log.v("@@@@*****", "draw ball");
        paint = new Paint();
        paint.setStyle(Style.FILL);
        paint.setColor(Color.RED);
         for (int j = 0; j < count; j++) {
        canvas.drawCircle(theBodies[j].getPosition().x, W_height - theBodies[j].getPosition().y, radius, paint);
        Log.v("@@@@*****", "draw ball");
         }
    }       

    @Override
    public boolean onTouchEvent(MotionEvent event) {
          switch (event.getAction()) {
          case MotionEvent.ACTION_DOWN:
              Log.v("@@@@*****", "Add ball");
             addBall((int)event.getX(),(int)event.getY());
          }
          return true;
    }

        @Override
        public void surfaceChanged(SurfaceHolder holder, int format,
                int width, int height) {
            // TODO Auto-generated method stub

        }

        @Override
        public void surfaceCreated(SurfaceHolder holder) {
             Log.d(TAG,"Surface Created");

        }

        @Override
        public void surfaceDestroyed(SurfaceHolder holder) {
            // TODO Auto-generated method stub

        }

  }

Answer 1

Probably a duplication of Extended SurfaceView's onDraw() method never called. Try adding setWillNotDraw(false) to your constructor.