android surfaceview crashes when go to background

Question

my app get crashed when the surfaceview goes to background by recieving call or exit and return to the app. i read that surfacedestroyed doesnt get call on these situations but the solutions that were given didnt work for me. i will be gratefull if someone can help me with my code. thanks

public GameLoopThread(GameView view)
{

this.view=view;
}
public void setRunning (boolean run)
{
    running=run;
}
@Override
public void run() {

    long ticksPerSecond=1000/FPS;
    long startTime;
    long sleepTime;
    while (running)
    {
        Canvas c=null;
        startTime=System.currentTimeMillis();
        try {
        c=view.getHolder().lockCanvas();
        synchronized (view.getHolder()) {
            view.onDraw(c);
        }

        } catch (Exception e) {
            // TODO: handle exception
        }
        finally{
            if(c!=null)
            view.getHolder().unlockCanvasAndPost(c);
        }
        sleepTime=ticksPerSecond-(System.currentTimeMillis()-startTime);
        try
        {if(sleepTime>0)
            sleep(sleepTime);
        else
            sleep(10);

        }
        catch(Exception e){}

        synchronized (mPauseLock) {
            while (!running) {
                try {
                    mPauseLock.wait();
                } catch (InterruptedException e) {
                }
            }
        }
    }

and in the surfaceview:
 public void surfaceDestroyed(SurfaceHolder holder) {
 if(gameLoopThread.isAlive())
            {
                boolean retry = true;
                gameLoopThread.setRunning(false);
                while (retry) {
                    try {
                        gameLoopThread.join();
                        retry = false;
                    } catch (InterruptedException e) {
                    }
                }
            }
            }

            @Override
            public void surfaceCreated(SurfaceHolder holder) {
                if(!gameLoopThread.isAlive())
                    {           

                     gameLoopThread.setRunning(true);
                     gameLoopThread.start();

                    }
            }

---

maybe the logcat will help:

10-22 09:35:06.310: DEBUG/Buddies--------------------------->(10985): Service:OnReceive ACTION_HOME_RESUME called 10-22 09:35:06.315: DEBUG/AndroidRuntime(3275): Shutting down VM 10-22 09:35:06.315: WARN/dalvikvm(3275): threadid=1: thread exiting with uncaught exception (group=0x4001e578) 10-22 09:35:06.315: ERROR/AndroidRuntime(3275): FATAL EXCEPTION: main 10-22 09:35:06.315: ERROR/AndroidRuntime(3275): java.lang.NullPointerException 10-22 09:35:06.315: ERROR/AndroidRuntime(3275): at tomer.idunku3.GameView$1.surfaceDestroyed(GameView.java:126) 10-22 09:35:06.315: ERROR/AndroidRuntime(3275): at android.view.SurfaceView.reportSurfaceDestroyed(SurfaceView.java:613) 10-22 09:35:06.315: ERROR/AndroidRuntime(3275): at android.view.SurfaceView.updateWindow(SurfaceView.java:498) 10-22 09:35:06.315: ERROR/AndroidRuntime(3275): at android.view.SurfaceView.updateWindow(SurfaceView.java:407) 10-22 09:35:06.315: ERROR/AndroidRuntime(3275): at android.view.SurfaceView.onWindowVisibilityChanged(SurfaceView.java:217) 10-22 09:35:06.315: ERROR/AndroidRuntime(3275): at android.view.View.dispatchWindowVisibilityChanged(View.java:4080) 10-22 09:35:06.315: ERROR/AndroidRuntime(3275): at android.view.ViewGroup.dispatchWindowVisibilityChanged(ViewGroup.java:720) 10-22 09:35:06.315: ERROR/AndroidRuntime(3275): at android.view.ViewGroup.dispatchWindowVisibilityChanged(ViewGroup.java:720) 10-22 09:35:06.315: ERROR/AndroidRuntime(3275): at android.view.ViewRoot.performTraversals(ViewRoot.java:790) 10-22 09:35:06.315: ERROR/AndroidRuntime(3275): at android.view.ViewRoot.handleMessage(ViewRoot.java:1868) 10-22 09:35:06.315: ERROR/AndroidRuntime(3275): at android.os.Handler.dispatchMessage(Handler.java:99) 10-22 09:35:06.315: ERROR/AndroidRuntime(3275): at android.os.Looper.loop(Looper.java:123) 10-22 09:35:06.315: ERROR/AndroidRuntime(3275): at android.app.ActivityThread.main(ActivityThread.java:3691) 10-22 09:35:06.315: ERROR/AndroidRuntime(3275): at java.lang.reflect.Method.invokeNative(Native Method) 10-22 09:35:06.315: ERROR/AndroidRuntime(3275): at java.lang.reflect.Method.invoke(Method.java:507) 10-22 09:35:06.315: ERROR/AndroidRuntime(3275): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:847) 10-22 09:35:06.315: ERROR/AndroidRuntime(3275): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:605) 10-22 09:35:06.315: ERROR/AndroidRuntime(3275): at dalvik.system.NativeStart.main(Native Method) 10-22 09:35:06.320: ERROR/(18080): Dumpstate > /data/log/dumpstate_app_error

Answer 1

My application randomly (pretty often) crashed when returning to previous activity. Turns out the "try" statement is not working as expected as Canvas c can be null still after the getHolder() method.

while (running) {
    Canvas c=null;
    startTime=System.currentTimeMillis();
    try {
        c=view.getHolder().lockCanvas();
        if(c!=null){ // <- this is the line of code I had to add to make it work
            synchronized (view.getHolder()) {
                view.onDraw(c);
            }
        }
    } catch (Exception e) {}
    finally{
        if(c!=null)
        view.getHolder().unlockCanvasAndPost(c);
    }
    //...
}

Answer 2

I dont think this part is necessary:

synchronized (mPauseLock) {
        while (!running) {
            try {
                mPauseLock.wait();
            } catch (InterruptedException e) {
            }
        }
    }

If you use this, you'll need to notify in order to release the lock on wait(); But try using the same code, with out the synchronized(mPauseLock)

EDIT:

The solution for your problem when you press on the Home button, the application crashes, do this:

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    gameView = new GameView(this);
    setContentView(gameView); 
}

@Override
public void onPause(){
    super.onPause();
    gameView.gameLoopThread.setRunning(false);
    finish();
}

And in GameView (SurfaceView) create the constructor:

public GameLoopThread gameLoopThread;

public GameView(Context context) {
    super(context);
    gameLoopThread = new GameLoopThread(this);
}