white screen - Page 771

Android draw using SurfaceView and Thread

- by Morten Høgseth

I am trying to draw a ball to my screen using 3 classes. I have read a little about this and I found a code snippet that works using the 3 classes on one page, Playing with graphics in Android I altered the code so that I have a ball that is moving and shifts direction when hitting the wall like the picture below (this is using the code in the link). Now I like to separate the classes into 3 different pages for not making everything so crowded, everything is set up the same way. Here are the 3 classes I have. BallActivity.java Ball.java BallThread.java package com.brick.breaker; import android.app.Activity; import android.os.Bundle; import android.view.Window; import android.view.WindowManager; public class BallActivity extends Activity { private Ball ball; @Override protected void onCreate(Bundle savedInstanceState) { // TODO Auto-generated method stub super.onCreate(savedInstanceState); requestWindowFeature(Window.FEATURE_NO_TITLE); getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,WindowManager.LayoutParams.FLAG_FULLSCREEN); ball = new Ball(this); setContentView(ball); } @Override protected void onPause() { // TODO Auto-generated method stub super.onPause(); setContentView(null); ball = null; finish(); } } package com.brick.breaker; import android.content.Context; import android.graphics.Bitmap; import android.graphics.BitmapFactory; import android.graphics.Canvas; import android.view.SurfaceHolder; import android.view.SurfaceView; public class Ball extends SurfaceView implements SurfaceHolder.Callback { private BallThread ballThread = null; private Bitmap bitmap; private float x, y; private float vx, vy; public Ball(Context context) { super(context); // TODO Auto-generated constructor stub bitmap = BitmapFactory.decodeResource(getResources(), R.drawable.ball); x = 50.0f; y = 50.0f; vx = 10.0f; vy = 10.0f; getHolder().addCallback(this); ballThread = new BallThread(getHolder(), this); } protected void onDraw(Canvas canvas) { update(canvas); canvas.drawBitmap(bitmap, x, y, null); } public void update(Canvas canvas) { checkCollisions(canvas); x += vx; y += vy; } public void checkCollisions(Canvas canvas) { if(x - vx < 0) { vx = Math.abs(vx); } else if(x + vx > canvas.getWidth() - getBitmapWidth()) { vx = -Math.abs(vx); } if(y - vy < 0) { vy = Math.abs(vy); } else if(y + vy > canvas.getHeight() - getBitmapHeight()) { vy = -Math.abs(vy); } } public int getBitmapWidth() { if(bitmap != null) { return bitmap.getWidth(); } else { return 0; } } public int getBitmapHeight() { if(bitmap != null) { return bitmap.getHeight(); } else { return 0; } } public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) { // TODO Auto-generated method stub } public void surfaceCreated(SurfaceHolder holder) { // TODO Auto-generated method stub ballThread.setRunnable(true); ballThread.start(); } public void surfaceDestroyed(SurfaceHolder holder) { // TODO Auto-generated method stub boolean retry = true; ballThread.setRunnable(false); while(retry) { try { ballThread.join(); retry = false; } catch(InterruptedException ie) { //Try again and again and again } break; } ballThread = null; } } package com.brick.breaker; import android.graphics.Canvas; import android.view.SurfaceHolder; public class BallThread extends Thread { private SurfaceHolder sh; private Ball ball; private Canvas canvas; private boolean run = false; public BallThread(SurfaceHolder _holder,Ball _ball) { sh = _holder; ball = _ball; } public void setRunnable(boolean _run) { run = _run; } public void run() { while(run) { canvas = null; try { canvas = sh.lockCanvas(null); synchronized(sh) { ball.onDraw(canvas); } } finally { if(canvas != null) { sh.unlockCanvasAndPost(canvas); } } } } public Canvas getCanvas() { if(canvas != null) { return canvas; } else { return null; } } } Here is a picture that shows the outcome of these classes. I've tried to figure this out but since I am pretty new to Android development I thought I could ask for help. Does any one know what is causing the ball to be draw like that? The code is pretty much the same as the one in the link and I have tried to experiment to find a solution but no luck. Thx in advance for any help=)

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