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Objects getting nulled when activity leaves foreground.


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#1 Funkyjive   Members   -  Reputation: 125

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Posted 05 March 2012 - 11:55 PM

I am new to Android development so be patient with me. I have got touch, physics, and rendering figured out but have hit my first huge problem.

The game starts up and runs fine. If I hit the home button the program leaves the foreground (as expected). If I navigate to a list of my applications and try to start it again it crashes with a null pointer.

I have looked into and done some googling at it looks like when an activity leaves the foreground it does not actually die. It looks like it may or may not but that is dependent upon the resources available for new starting apps. Long story short I was able to track down the issue. It appears that a variable (one of my objects) is coming back null when the program returns to the foreground. In my reasearch I have also discovered that an activity can save off basic variable types and later read them back in. My question is how would I do this for a non-primitive object?

Here is some relevant code to explain how I have my game setup (perhaps i have just made a flaw in the basic design of the activity.
public class Android_Main extends Activity {

/* Main program entry point. Create the main game framework that will create the game object. */
    public void onCreate(Bundle saved_instance_state) {
	 /* Not sure what happens in the super class but do it anyways (all the tutorials I have seen do it). */
	 super.onCreate(saved_instance_state);
	
	 /* These will give full screen. */
	 this.requestWindowFeature(Window.FEATURE_NO_TITLE);
	 getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN);
	
	 WindowManager window_manager = (WindowManager) getSystemService(WINDOW_SERVICE);
	 Display display = window_manager.getDefaultDisplay();
	
	 /* Create the opengl view which uses the game framework. */
	 game_framework = new Game_Framework(this, display);
	 gl_surface = new GLSurfaceView(this);
	 gl_surface.setRenderer(game_framework);
	 setContentView(gl_surface);
	
	 /* Register acceleration sensor to get gravity. The handler function is in game framework. */
	 SensorManager sensorManager = (SensorManager) this.getSystemService(SENSOR_SERVICE);  
	    sensorManager.registerListener(game_framework, sensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER), SensorManager.SENSOR_DELAY_FASTEST);
    }
   
    /* Automatically called when the application freezes. Let the opengl surface/game framework know. */
    protected void onPause() {
  super.onPause();
  gl_surface.onPause();
}
   
    /* Automatically called when the application unfreezes. Let the opengl surface/game framework know. */
    protected void onResume() {
  super.onResume();
  gl_surface.onResume();
}
   
//////OMMITED FOR SPACE
  
    /* OpenGL surface */
    private GLSurfaceView gl_surface;
   
    /* Game framework */
    Game_Framework game_framework;
}

Long story short, there is a static variable that I use to keep track of game state. (This static variable seems to hold its value across the gap between when the activity leaves the foreground and when it restarts. Since the game framework gets created new each time it starts and the game state variable says, yes we are past the loading of some objects go ahead and try to render them I hit the null pointer issue.
"I would rather be in the boat with a drink on the rocks, than in the drink with a boat on the rocks" -Unknown

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#2 Funkyjive   Members   -  Reputation: 125

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Posted 06 March 2012 - 12:37 AM

Ok looks like I solved the problem and the solution was much easier than I thought. My game framework class is a level of abstraction. In the onSurfaceCreated method I was creating a new instace of my game class. The onSurfaceCreated was being called each time the activity was taken back to the foreground thus nuking my game object with a new instance.
"I would rather be in the boat with a drink on the rocks, than in the drink with a boat on the rocks" -Unknown




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