core/src/in/srain/cube/app/CubeFragmentActivity.java
@Override
    public void onBackPressed() {

        // process back for fragment
        if (processBackPressed()) {
            return;
        }

        // process back for fragment
        boolean enableBackPressed = true;
        if (mCurrentFragment != null) {
            enableBackPressed = !mCurrentFragment.processBackPressed();
        }
        if (enableBackPressed) {
            int cnt = getSupportFragmentManager().getBackStackEntryCount();
            if (cnt <= 1 && isTaskRoot()) {
                String closeWarningHint = getCloseWarning();
                if (!mCloseWarned && !TextUtils.isEmpty(closeWarningHint)) {
                    Toast toast = Toast.makeText(this, closeWarningHint, Toast.LENGTH_SHORT);
                    toast.show();
                    mCloseWarned = true;
                } else {
                    doReturnBack();
                }
            } else {
                mCloseWarned = false;
                doReturnBack();
            }
        }
    }
@Override
    public void onBackPressed() {

        // process back for fragment
        if (processBackPressed()) {
            return;
        }

        // process back for fragment
        boolean enableBackPressed = true;
        if (mCurrentFragment != null) {
            enableBackPressed = !mCurrentFragment.processBackPressed();
        }
        if (enableBackPressed) {
            int cnt = getSupportFragmentManager().getBackStackEntryCount();
            if (cnt <= 1 && isTaskRoot()) {
                String closeWarningHint = getCloseWarning();
                if (!mCloseWarned && !TextUtils.isEmpty(closeWarningHint)) {
                    Toast toast = Toast.makeText(this, closeWarningHint, Toast.LENGTH_SHORT);
                    toast.show();
                    mCloseWarned = true;
                } else {
                    doReturnBack();
                }
            } else {
                mCloseWarned = false;
                doReturnBack();
            }
        }
    }
process back pressed