Android - How To Override the "Back" button so it doesn't Finish() my Activity?

Question

I currently have an Activity that when it gets displayed a Notification will also get displayed in the Notification bar.

This is so that when the User presses home and the Activity gets pushed to the background they can get back to the Activity via the Notification.

The problem arises when a User presses the back button, my Activity gets destroyed but the Notification remains as I want the user to be able to press back but still be able to get to the Activity via the Notification. But when a USER tries this I get Null Pointers as its trying to start a new activity rather than bringing back the old one.

So essentially I want the Back button to act the exact same as the Home button and here is how I have tried so far:

---

        @Override
        public boolean onKeyDown(int keyCode, KeyEvent event)  {
            if (Integer.parseInt(android.os.Build.VERSION.SDK) < 5
                    && keyCode == KeyEvent.KEYCODE_BACK
                    && event.getRepeatCount() == 0) {
                Log.d("CDA", "onKeyDown Called");
                onBackPressed();
            }

            return super.onKeyDown(keyCode, event);
        }

        public void onBackPressed() {
            Log.d("CDA", "onBackPressed Called");
            Intent setIntent = new Intent(Intent.ACTION_MAIN);
            setIntent.addCategory(Intent.CATEGORY_HOME);
            setIntent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
            startActivity(setIntent); 

            return;
        }   

---

However the above code still seems to allow my Activity to be destroyed, How can I stop my Activity from being destroyed when the back button is pressed?

Answer 1

I think what you want is not to override the back button (that just doesn't seem like a good idea - Android OS defines that behavior, why change it?), but to use the Activity Lifecycle and persist your settings/data in the onSaveInstanceState(Bundle) event.

@Override
onSaveInstanceState(Bundle frozenState) {
    frozenState.putSerializable("object_key",
        someSerializableClassYouWantToPersist);
    // etc. until you have everything important stored in the bundle
}

Then you use onCreate(Bundle) to get everything out of that persisted bundle and recreate your state.

@Override
onCreate(Bundle savedInstanceState) {
    mCustomObject = savedInstanceState.getSerializable("object_key");
    // etc. until you have reloaded everything you stored
}

Consider the above psuedo-code to point you in the right direction. Reading up on the Activity Lifecycle should help you determine the best way to accomplish what you're looking for.

Answer 2

remove your key listener or return true when you have KEY_BACK

you just need the following to catch back key (make sure not to call super)

Also, if you plan on having a service run in the background, make sure to look at startForeground() and make sure to have an ongoing notification or android will kill your service if it needs to free memory

@overide
public void onBackPressed() {
   Log.d("CDA", "onBackPressed Called");
   Intent setIntent = new Intent(Intent.ACTION_MAIN);
   setIntent.addCategory(Intent.CATEGORY_HOME);
   setIntent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
   startActivity(setIntent);
   return;
}