Force close on resuming an app using SurfaceView

First, note that exactly the same thing happens with the LunarLander example. Anyways, this works great until I leave the app and try to return to it, whereupon I get a force close (IllegalThreadStateException).

MainGameActivity:

package com.tests.testgame1;

import android.app.Activity;
import android.os.Bundle;
import android.util.Log;

public class MainGameActivity extends Activity {

    private static MainGameView mainGameView;
    //private static Thread mainGameThread;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        mainGameView = new MainGameView(getApplicationContext());
        //mainGameThread = mainGameView.getThread();


//        if (savedInstanceState == null) {
//            // we were just launched: set up a new game
//          mainGameThread.setState(mainGameThread.STATE_READY);
//            Log.w(this.getClass().getName(), "SIS is null");
//        } else {
//            // we are being restored: resume a previous game
//        开发者_JS百科  mainGameThread.restoreState(savedInstanceState);
//            Log.w(this.getClass().getName(), "SIS is nonnull");
//        }

        setContentView(mainGameView);
    }

    @Override
    protected void onStart() {
        super.onStart();
        // The activity is about to become visible.
    }

    @Override
    protected void onResume() {
        super.onResume();
        mainGameView.unpauseGame();
        // The activity has become visible (it is now "resumed").
    }

    @Override
    protected void onPause() {
        super.onPause();
        mainGameView.pauseGame();
        // Another activity is taking focus (this activity is about to be "paused").
    }

    @Override
    protected void onStop() {
        super.onStop();
        // The activity is no longer visible (it is now "stopped")
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        // The activity is about to be destroyed.
    }





    @Override
    protected void onSaveInstanceState(Bundle outState) {
        // just have the View's thread save its state into our Bundle
        super.onSaveInstanceState(outState);
//        mainGameThread.saveState(outState);
        Log.w(this.getClass().getName(), "SIS called");
    }

}

MainGameView:

package com.tests.testgame1;



import android.content.Context;
import android.util.Log;
import android.view.SurfaceHolder;
import android.view.SurfaceHolder.Callback;
import android.view.SurfaceView;


public class MainGameView extends SurfaceView implements SurfaceHolder.Callback {

    private static final String TAG = "MainGameView"; //
    MainGameThread mainGameThread; //
    SurfaceHolder mainSurfaceHolder;
    Context mainContext;

    public MainGameView(Context context) {
        super(context);
        mainSurfaceHolder = getHolder();
        mainSurfaceHolder.addCallback(this);
        mainContext = context;
        mainGameThread = new MainGameThread(this, mainSurfaceHolder, mainContext);



        Log.d(TAG, "View created");



    }

    public Thread getThread() {
        return mainGameThread;
    }

    public void pauseGame() {
        mainGameThread.pauseGame();
    }


    public void unpauseGame() {
        //mainGameThread.start();
        mainGameThread.unpauseGame();
    }
    // 



    @Override
    public void onWindowFocusChanged(boolean hasWindowFocus) {
        if (!hasWindowFocus) mainGameThread.pauseGame();
    }


    public void onDraw()
    {

    }

    @Override
    public void surfaceChanged(SurfaceHolder arg0, int arg1, int arg2, int arg3) {
        // TODO Auto-generated method stub

    }

    @Override
    public void surfaceCreated(SurfaceHolder arg0) {

        mainGameThread.setRunning(true);
        mainGameThread.start();

    }

    @Override
    public void surfaceDestroyed(SurfaceHolder arg0) {

        // we have to tell thread to shut down & wait for it to finish, or else
        // it might touch the Surface after we return and explode
        boolean retry = true;
        mainGameThread.setRunning(false);
        while (retry) {
            try {
                mainGameThread.join();
                retry = false;
            } catch (InterruptedException e) {
            }
        }

    }

}

MainGameThread:

package com.tests.testgame1;

import android.content.Context;
import android.content.res.Resources;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Color;
import android.util.Log;
import android.view.SurfaceHolder;
import android.view.View;

class MainGameThread extends Thread {

    enum GameStates
    {
        GameStateRunning,
        GameStatePaused
    }

    private boolean running;
    private GameStates gameMode;
    private View view;
    private Context context;
    private SurfaceHolder surfaceHolder;

    Bitmap backgroundImage;

    public MainGameThread(View _view, SurfaceHolder _surfaceHolder, Context _context)
    {
        this.view = _view;
        this.surfaceHolder = _surfaceHolder;
        this.context = _context;
        this.running = true;
        this.gameMode = GameStates.GameStateRunning;

        Resources res = context.getResources();
        backgroundImage = BitmapFactory.decodeResource(res, R.drawable.background);
    }
    public void setRunning(boolean b) {
        running = b;
    }

    @Override
    public void run() {


        while (running) {
            if (gameMode == GameStates.GameStateRunning)
                    doStep();

            Canvas c = null;
            try {
                c = surfaceHolder.lockCanvas(null);
                synchronized (surfaceHolder) {

                    doDraw(c);
                }
            } finally {
                // do this in a finally so that if an exception is thrown
                // during the above, we don't leave the Surface in an
                // inconsistent state
                if (c != null) {
                    synchronized (surfaceHolder) {
                    surfaceHolder.unlockCanvasAndPost(c);
                    }  
                }
            }

        }


    }

    private void doDraw(Canvas canvas) {
        canvas.drawBitmap(backgroundImage, 0, 0, null);
        //canvas.drawColor(Color.BLUE);

    }

    private void doStep() {

    }

    public void pauseGame()
    { //
        synchronized (surfaceHolder) {
            if (gameMode == GameStates.GameStateRunning){
                gameMode = GameStates.GameStatePaused;
            }

        }
    }

    public void unpauseGame() {
        synchronized (surfaceHolder) {
            if (gameMode == GameStates.GameStatePaused){
                gameMode = GameStates.GameStateRunning;
            }

        }
    }


}

Stack trace:

Test Game [Android Application] 
    DalvikVM[localhost:8625]    
        Thread [<1> main] (Suspended (exception IllegalThreadStateException))   
            MainGameView(SurfaceView).updateWindow(boolean) line: 545   
            MainGameView(SurfaceView).onWindowVisibilityChanged(int) line: 206  
            MainGameView(View).dispatchWindowVisibilityChanged(int) line: 3891  
            FrameLayout(ViewGroup).dispatchWindowVisibilityChanged(int) line: 719   
            LinearLayout(ViewGroup).dispatchWindowVisibilityChanged(int) line: 719  
            PhoneWindow$DecorView(ViewGroup).dispatchWindowVisibilityChanged(int) line: 719 
            ViewRoot.performTraversals() line: 744  
            ViewRoot.handleMessage(Message) line: 1727  
            ViewRoot(Handler).dispatchMessage(Message) line: 99 
            Looper.loop() line: 123 
            ActivityThread.main(String[]) line: 4627    
            Method.invokeNative(Object, Object[], Class, Class[], Class, int, boolean) line: not available [native method]  
            Method.invoke(Object, Object...) line: 521  
            ZygoteInit$MethodAndArgsCaller.run() line: 868  
            ZygoteInit.main(String[]) line: 626 
            NativeStart.main(String[]) line: not available [native method]  
        Thread [<6> Binder Thread #2] (Running) 
        Thread [<5> Binder Thread #1] (Running) 
        Thread [<7> Binder Thread #3] (Running) 

Think you are having an issue in your surfaceCreated Method. When you are exiting the thread it is being terminated. Once this has occurred you can not call

mainGameThread.start();

Instead, inside surfaceCreated, first query the state of the thread first, then if it has been terminated, start a new one as you did in MainGameView,

if (mainGameThread .getState() == Thread.State.TERMINATED)
{

    mainGameThread = new MainGameThread(this, mainSurfaceHolder, mainContext);  
    mainGameThread.setRunning(true);
    mainGameThread.start();
}
else
{
    mainGameThread.setRunning(true);
    mainGameThread.start();
}