Question

I don’t know why , i can’t override back button: I tried everything I know to override my back button.

And fragment.addToBackStack(null) don’t work .

Any one have an explanation?

I am using android 3.0, and i have activity containing 4 frameLayout where i associate fragments.

@Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {
        if (keyCode == KeyEvent.KEYCODE_BACK) {

            return false;
        }
        return super.onKeyDown(keyCode, event);
    }

Answer 1

You should return true if you have handled the key event, this will stop any callbacks to propagate to the android os for handling of the event.
http://developer.android.com/reference/android/view/View.html#onKeyDown(int, android.view.KeyEvent)
So change from return false; to return true; and you should be good.
And do put some logging in there to make it clear what path is being executed 🙂