I am unable to run my program. The app gets crashed. I am trying to make the image move on the screen by touchEvent.
java.lang.NullPointerException: Attempt to invoke virtual method 'int com.example.swapnil.new1.model.conmponents.Speed.getxDirection()' on a null object reference
at com.example.swapnil.new1.GamePanel.update(GamePanel.java:89)
at com.example.swapnil.new1.MainThread.run(MainThread.java:32)
I have added the Speed class which I think is responsible for this exception. Suggest any updates.
Speed class has the getxDirection method which is causing the exception.
package com.example.swapnil.new1.model.conmponents;
public class Speed {
public static final int DIRECTION_RIGHT = 1;
public static final int DIRECTION_LEFT = -1;
public static final int DIRECTION_UP = -1;
public static final int DIRECTION_DOWN = 1;
private float xv = 1; // speed in x
private float yv = 1; // speed in y
private int xDirection = DIRECTION_RIGHT;
private int yDirection = DIRECTION_DOWN;
public Speed() {
this.xv = 1;
this.yv = 1;
}
public Speed(float xv, float yv) {
this.xv = xv;
this.yv = yv;
}
public float getXv() {
return xv;
}
public void setXv(float xv) {
this.xv = xv;
}
public float getYv() {
return yv;
}
public void setYv(float yv) {
this.yv = yv;
}
public int getxDirection() {
return xDirection;
}
public void setxDirection(int xDirection) {
this.xDirection = xDirection;
}
public int getyDirection() {
return yDirection;
}
public void setyDirection(int yDirection) {
this.yDirection = yDirection;
}
public void toggleXDirection() {
xDirection = xDirection * -1;
}
public void toggleYDirection() {
yDirection = yDirection * -1;
}
}
The MainThread class:
package com.example.swapnil.new1;
import android.graphics.Canvas;
import android.util.Log;
import android.view.SurfaceHolder;
public class MainThread extends Thread {
private static final String TAG = MainThread.class.getSimpleName();
private boolean running;
private SurfaceHolder surfaceHolder;
private GamePanel gamePanel;
public MainThread(SurfaceHolder surfaceHolder , GamePanel gamePanel) {
super();
this.surfaceHolder = surfaceHolder;
this.gamePanel = gamePanel;
}
public void setRunning(boolean running) {
this.running = running;
}
@Override
public void run() {
Canvas canvas;
Log.d(TAG , "Starting game loop");
while(running) {
canvas = null;
try {
canvas = this.surfaceHolder.lockCanvas();
synchronized (surfaceHolder) {
this.gamePanel.render(canvas);
this.gamePanel.update();
}
} finally {
if(canvas != null) {
surfaceHolder.unlockCanvasAndPost(canvas);
}
}
}
}
}
The GamePanel class:
import android.app.Activity;
import android.content.Context;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Color;
import android.util.Log;
import android.view.MotionEvent;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
import com.example.swapnil.new1.model.Droid;
import com.example.swapnil.new1.model.conmponents.Speed;
public class GamePanel extends SurfaceView implements
SurfaceHolder.Callback {
private static final String TAG = GamePanel.class.getSimpleName();
private MainThread thread;
private Droid droid;
public GamePanel(Context context) {
super(context);
getHolder().addCallback(this);
droid = new Droid(BitmapFactory.decodeResource(getResources(),R.drawable.droid_1),50,50);
thread = new MainThread(getHolder() , this);
setFocusable(true);
}
@Override
public void surfaceCreated(SurfaceHolder holder) {
thread.setRunning(true);
thread.start();
}
@Override
public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {
}
@Override
public void surfaceDestroyed(SurfaceHolder holder) {
boolean retry = true;
while (retry) {
try {
thread.join();
retry = false;
}catch (InterruptedException e) {
}
}
}
@Override
public boolean onTouchEvent(MotionEvent event) {
if (event.getAction() == MotionEvent.ACTION_DOWN) {
droid.handleActionDown((int)event.getX(),(int)event.getY());
if (event.getY() > getHeight() - 50) {
thread.setRunning(false);
((Activity)getContext()).finish();
} else {
Log.d(TAG , "Coords : x = " + event.getX() + ",y = " + event.getY());
}
}
if (event.getAction() == MotionEvent.ACTION_MOVE) {
if (droid.isTouched()) {
droid.setX((int)event.getX());
droid.setY((int) event.getY());
}
}
if (event.getAction() == MotionEvent.ACTION_UP) {
if (droid.isTouched()) {
droid.setTouched(false);
}
}
return true;
}
// changed protected to public
protected void render(Canvas canvas) {
canvas.drawColor(Color.BLACK);
droid.draw(canvas);
}
public void update() {
// collision with right
if (droid.getSpeed().getxDirection() == Speed.DIRECTION_RIGHT &&
droid.getX() + droid.getBitmap().getWidth()/2 >= getWidth()) {
droid.getSpeed().toggleXDirection();
}
//collision with left
if (droid.getSpeed().getxDirection() == Speed.DIRECTION_LEFT &&
droid.getX() - droid.getBitmap().getWidth()/2 <= 0) {
droid.getSpeed().toggleXDirection();
}
// collision with down
if (droid.getSpeed().getyDirection() == Speed.DIRECTION_DOWN &&
droid.getY() + droid.getBitmap().getHeight()/2 >= getHeight()) {
droid.getSpeed().toggleYDirection();
}
//collision with up
if (droid.getSpeed().getyDirection() == Speed.DIRECTION_UP &&
droid.getY() - droid.getBitmap().getHeight()/2 <= 0) {
droid.getSpeed().toggleYDirection();
}
droid.update();
}
}
