I tried to make a single ball bouncing to dynamic ball bouncing . Eg: here the number of circles is 50. But I am getting error while trying to make the circles dynamic (Model) .How do I make it work and make the model/circle dynamic.In this case 50 circles ? I really appreciate any help. Thanks in Advance.
package com.stuffthathappens.games;
import static android.hardware.SensorManager.DATA_X;
import static android.hardware.SensorManager.DATA_Y;
import static android.hardware.SensorManager.SENSOR_ACCELEROMETER;
import static android.hardware.SensorManager.SENSOR_DELAY_GAME;
import java.util.concurrent.TimeUnit;
import android.app.Activity;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.hardware.SensorListener;
import android.hardware.SensorManager;
import android.os.Bundle;
import android.os.Vibrator;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
import android.view.SurfaceHolder.Callback;
/**
* This activity shows a ball that bounces around. The phone's
* accelerometer acts as gravity on the ball. When the ball hits
* the edge, it bounces back and triggers the phone vibrator.
*/
@SuppressWarnings("deprecation")
public class BouncingBallActivity extends Activity implements Callback, SensorListener {
private static final int BALL_RADIUS =20;
private SurfaceView surface;
private SurfaceHolder holder;
private GameLoop gameLoop;
private Paint backgroundPaint;
private Paint ballPaint;
private SensorManager sensorMgr;
private long lastSensorUpdate = -1;
private Paint ballPaintyellow;
private BouncingBallModel[] model;
int Totalcircles=50;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.bouncing_ball);
for (int i = 0; i < Totalcircles; i++) {
model[i] = new BouncingBallModel(BALL_RADIUS);
}
surface = (SurfaceView) findViewById(R.id.bouncing_ball_surface);
holder = surface.getHolder();
surface.getHolder().addCallback(this);
backgroundPaint = new Paint();
backgroundPaint.setColor(Color.WHITE);
ballPaint = new Paint();
ballPaint.setColor(Color.BLUE);
ballPaint.setAntiAlias(true);
ballPaintyellow = new Paint();
ballPaintyellow.setColor(Color.YELLOW);
ballPaintyellow.setAntiAlias(true);
}
@Override
protected void onPause() {
super.onPause();
for (int i = 0; i < Totalcircles; i++) {
model[i].setVibrator(null);
}
sensorMgr.unregisterListener(this, SENSOR_ACCELEROMETER);
sensorMgr = null;
for (int i = 0; i < Totalcircles; i++) {
model[i].setAccel(0, 0);
}
}
@Override
protected void onResume() {
super.onResume();
sensorMgr = (SensorManager) getSystemService(SENSOR_SERVICE);
boolean accelSupported = sensorMgr.registerListener(this,
SENSOR_ACCELEROMETER,
SENSOR_DELAY_GAME);
if (!accelSupported) {
// on accelerometer on this device
sensorMgr.unregisterListener(this, SENSOR_ACCELEROMETER);
// TODO show an error
}
// NOTE 1: you cannot get system services before onCreate()
// NOTE 2: AndroidManifest.xml must contain this line:
// <uses-permission android:name="android.permission.VIBRATE"/>
Vibrator vibrator = (Vibrator) getSystemService(Activity.VIBRATOR_SERVICE);
for (int i = 0; i < Totalcircles; i++) {
model[i].setVibrator(vibrator);
}
}
public void surfaceChanged(SurfaceHolder holder, int format, int width,
int height) {
for (int i = 0; i < Totalcircles; i++) {
model[i].setSize(width, height);
}
}
public void surfaceCreated(SurfaceHolder holder) {
gameLoop = new GameLoop();
gameLoop.start();
}
private void draw() {
// thread safety - the SurfaceView could go away while we are drawing
Canvas c = null;
try {
// NOTE: in the LunarLander they don't have any synchronization here,
// so I guess this is OK. It will return null if the holder is not ready
c = holder.lockCanvas();
// this needs to synchronize on something
if (c != null) {
doDraw(c);
}
} finally {
if (c != null) {
holder.unlockCanvasAndPost(c);
}
}
}
private void doDraw(Canvas c) {
int width = c.getWidth();
int height = c.getHeight();
c.drawRect(0, 0, width, height, backgroundPaint);
///
float ballX[]=new float[50], ballY[]=new float[50];
for (int i = 0; i < Totalcircles; i++) {
synchronized (model[i].LOCK) {
ballX[i] = model[i].ballPixelX;
ballY[i] = model[i].ballPixelY;
}
}
//
for (int i = 0; i < Totalcircles; i++) {
c.drawCircle(ballX[i], ballY[i], BALL_RADIUS, ballPaint);
}
}
public void surfaceDestroyed(SurfaceHolder holder) {
try {
for (int i = 0; i < Totalcircles; i++) {
model[i].setSize(0,0);
}
gameLoop.safeStop();
} finally {
gameLoop = null;
}
}
private class GameLoop extends Thread {
private volatile boolean running = true;
public void run() {
while (running) {
try {
// don't like this hardcoding
TimeUnit.MILLISECONDS.sleep(5);
draw();
for (int i = 0; i < Totalcircles; i++) {
model[i].updatePhysics();
}
} catch (InterruptedException ie) {
running = false;
}
}
}
public void safeStop() {
running = false;
interrupt();
}
}
public void onAccuracyChanged(int sensor, int accuracy) {
}
public void onSensorChanged(int sensor, float[] values) {
if (sensor == SENSOR_ACCELEROMETER) {
long curTime = System.currentTimeMillis();
// only allow one update every 50ms, otherwise updates
// come way too fast
if (lastSensorUpdate == -1 || (curTime - lastSensorUpdate) > 50) {
lastSensorUpdate = curTime;
for (int i = 0; i < Totalcircles; i++) {
model[i].setAccel(values[DATA_X], values[DATA_Y]);
}
}
}
}
}
model.java
package com.stuffthathappens.games;
import java.util.concurrent.atomic.AtomicReference;
import android.os.Vibrator;
/**
* This data model tracks the width and height of the playing field along
* with the current position of a ball.
*/
public class BouncingBallModel {
// the ball speed is meters / second. When we draw to the screen,
// 1 pixel represents 1 meter. That ends up too slow, so multiply
// by this number. Bigger numbers speeds things up.
private final float pixelsPerMeter = 10;
private final int ballRadius;
// these are public, so make sure you synchronize on LOCK
// when reading these. I made them public since you need to
// get both X and Y in pairs, and this is more efficient than
// getter methods. With two getters, you'd still need to
// synchronize.
public float ballPixelX, ballPixelY;
private int pixelWidth, pixelHeight;
// values are in meters/second
private float velocityX, velocityY;
// typical values range from -10...10, but could be higher or lower if
// the user moves the phone rapidly
private float accelX, accelY;
/**
* When the ball hits an edge, multiply the velocity by the rebound.
* A value of 1.0 means the ball bounces with 100% efficiency. Lower
* numbers simulate balls that don't bounce very much.
*/
private static final float rebound = 0.8f;
// if the ball bounces and the velocity is less than this constant,
// stop bouncing.
private static final float STOP_BOUNCING_VELOCITY = 2f;
private volatile long lastTimeMs = -1;
public final Object LOCK = new Object();
private AtomicReference<Vibrator> vibratorRef =
new AtomicReference<Vibrator>();
public BouncingBallModel(int ballRadius) {
this.ballRadius = ballRadius;
}
public void setAccel(float ax, float ay) {
synchronized (LOCK) {
this.accelX = ax;
this.accelY = ay;
}
}
public void setSize(int width, int height) {
synchronized (LOCK) {
this.pixelWidth = width;
this.pixelHeight = height;
}
}
public int getBallRadius() {
return ballRadius;
}
/**
* Call this to move the ball to a particular location on the screen. This
* resets the velocity to zero, but the acceleration doesn't change so
* the ball should start falling shortly.
*/
public void moveBall(int ballX, int ballY) {
synchronized (LOCK) {
this.ballPixelX = ballX;
this.ballPixelY = ballY;
velocityX = 0;
velocityY = 0;
}
}
public void updatePhysics() {
// copy everything to local vars (hence the 'l' prefix)
float lWidth, lHeight, lBallX, lBallY, lAx, lAy, lVx, lVy;
synchronized (LOCK) {
lWidth = pixelWidth;
lHeight = pixelHeight;
lBallX = ballPixelX;
lBallY = ballPixelY;
lVx = velocityX;
lVy = velocityY;
lAx = accelX;
lAy = -accelY;
}
if (lWidth <= 0 || lHeight <= 0) {
// invalid width and height, nothing to do until the GUI comes up
return;
}
long curTime = System.currentTimeMillis();
if (lastTimeMs < 0) {
lastTimeMs = curTime;
return;
}
long elapsedMs = curTime - lastTimeMs;
lastTimeMs = curTime;
// update the velocity
// (divide by 1000 to convert ms to seconds)
// end result is meters / second
lVx += ((elapsedMs * lAx) / 1000) * pixelsPerMeter;
lVy += ((elapsedMs * lAy) / 1000) * pixelsPerMeter;
// update the position
// (velocity is meters/sec, so divide by 1000 again)
lBallX += ((lVx * elapsedMs) / 1000) * pixelsPerMeter;
lBallY += ((lVy * elapsedMs) / 1000) * pixelsPerMeter;
boolean bouncedX = false;
boolean bouncedY = false;
if (lBallY - ballRadius < 0) {
lBallY = ballRadius;
lVy = -lVy * rebound;
bouncedY = true;
} else if (lBallY + ballRadius > lHeight) {
lBallY = lHeight - ballRadius;
lVy = -lVy * rebound;
bouncedY = true;
}
if (bouncedY && Math.abs(lVy) < STOP_BOUNCING_VELOCITY) {
lVy = 0;
bouncedY = false;
}
if (lBallX - ballRadius < 0) {
lBallX = ballRadius;
lVx = -lVx * rebound;
bouncedX = true;
} else if (lBallX + ballRadius > lWidth) {
lBallX = lWidth - ballRadius;
lVx = -lVx * rebound;
bouncedX = true;
}
if (bouncedX && Math.abs(lVx) < STOP_BOUNCING_VELOCITY) {
lVx = 0;
bouncedX = false;
}
// safely copy local vars back to object fields
synchronized (LOCK) {
ballPixelX = lBallX;
ballPixelY = lBallY;
velocityX = lVx;
velocityY = lVy;
}
if (bouncedX || bouncedY) {
Vibrator v = vibratorRef.get();
if (v != null) {
v.vibrate(20L);
}
}
}
public void setVibrator(Vibrator v) {
vibratorRef.set(v);
}
}
Logcat error:
FATAL EXCEPTION: main
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.stuffthathappens.games/com.stuffthathappens.games.BouncingBallActivity}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2194)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2229)
at android.app.ActivityThread.access$600(ActivityThread.java:139)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1261)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:4945)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at com.stuffthathappens.games.BouncingBallActivity.onCreate(BouncingBallActivity.java:52)
at android.app.Activity.performCreate(Activity.java:4531)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1071)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2150)
