Exit App on Back Button Press not working

Question

I would like my application to quit if the user presses back at a certain activity. The following is the code for that activity.

public class MainActivity extends FragmentActivity implements DenkoListFragment.ListSelectListener {

    private SlidingMenu menu;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        displayView(0);

        menu = new SlidingMenu(this);
        menu.setTouchModeAbove(SlidingMenu.TOUCHMODE_FULLSCREEN);
        menu.setShadowWidthRes(R.dimen.shadow_width);
        menu.setShadowDrawable(R.drawable.shadow);
        menu.setBehindOffsetRes(R.dimen.slidingmenu_offset);
        menu.setFadeDegree(0.35f);
        menu.attachToActivity(this, SlidingMenu.SLIDING_CONTENT);
        menu.setMenu(R.layout.menu_frame);

        menu.setSelected(true);

        getSupportFragmentManager()
                .beginTransaction()
                .replace(R.id.menu_frame, new DenkoListFragment())
                .commit();
    }

    private void displayView(int position) {

        Fragment fragment = null;
        switch (position) {
            case 0:
                fragment = new MainViewFragment();
                break;
            case 1:
                fragment = new StationViewFragment();
                break;
            case 2:
                fragment = new MapViewFragment();
                break;

            default:
                break;
        }

        if (fragment != null) {
            FragmentManager fragmentManager = getSupportFragmentManager();
            fragmentManager.beginTransaction()
                    .replace(R.id.content_frame, fragment).commit();
        } else {

        }
    }

    @Override
    public void select(int index) {
        displayView(index);
        menu.showContent();
    }

    @Override
    public void onBackPressed() {
        if (menu.isMenuShowing()) {
            menu.showContent();
        } else {
            new AlertDialog.Builder(this).setIcon(android.R.drawable.ic_dialog_alert).setTitle("Exit")
                    .setMessage("Are you sure you want to exit?")
                    .setPositiveButton("Yes", new DialogInterface.OnClickListener() {
                        @Override
                        public void onClick(DialogInterface dialog, int which) {
                            finish();
                            System.exit(0);
                        }
                    }).setNegativeButton("No", null).show();
        }
    }

}

It takes the app two back presses (and two confirmations) to exit. What explains this behaviour and is there any way to resolve this?

Answer 1

Remove below snippet from onBackPress() Method. It will handle by SlideMenu only.

if (menu.isMenuShowing()) {
     menu.showContent();
}

Code from SlidingFragmentActivity call onBackPress :

@Override
public boolean onKeyUp(int keyCode, KeyEvent event) {
    boolean b = mHelper.onKeyUp(keyCode, event);
    if (b) return b;
    return super.onKeyUp(keyCode, event);
} 

mHelper.onKeyUp(keyCode, event) will call a Method of SlidingActivityHelper :

public boolean onKeyUp(int keyCode, KeyEvent event) {
    if (keyCode == KeyEvent.KEYCODE_BACK && mSlidingMenu.isMenuShowing()) {
        showContent();   //Close the SlidingMenu and show the content view.
        return true;
    }
    return false;
}

Answer 2

super.onBackPressed(); will do what ever you want,just include super.onBackPressed(); instead of System.exit(0); ,because it will call the onBackpressed method of Activity .So, onDestroy method get call properly.

 new AlertDialog.Builder(this).setIcon(android.R.drawable.ic_dialog_alert).setTitle("Exit")
                            .setMessage("Are you sure you want to exit?")
                            .setPositiveButton("Yes", new DialogInterface.OnClickListener() {
                                @Override
                                public void onClick(DialogInterface dialog, int which) {
                                    finish();
                                    super.onBackPressed();
                                }
                            }).setNegativeButton("No", null).show();