On clicking Hamberger icon navigation drawer doesn't open

Question

I am getting a weird problem since 3 days. I searched a lot but was unable to point out my problem.

This is my setup method inside navigatonDrawer class which I had called from the MainActivity.

    public void setUp(DrawerLayout navDrawer, final Toolbar toolbar) {
        mDrawerLayout = navDrawer;
        mDrawerToggle = new ActionBarDrawerToggle(getActivity(), navDrawer, R.string.open, R.string.close) {
        @Override
        public void onDrawerOpened(View drawerView) {
            super.onDrawerOpened(drawerView);
            title= (String) toolbar.getTitle();
            toolbar.setTitle("Menu");
            getActivity().invalidateOptionsMenu();
        }

        @Override
        public void onDrawerClosed(View drawerView) {
            super.onDrawerClosed(drawerView);
            if(toolbar.getTitle()=="Menu"){
                toolbar.setTitle(title);
            }
            getActivity().invalidateOptionsMenu();
        }

    };
    mDrawerLayout.setDrawerListener(mDrawerToggle);
    mDrawerLayout.post(new Runnable() {

        @Override
        public void run() {
            mDrawerToggle.syncState();
        }
    });
}

My hamburger icon runs with charming animation but on clicking the icon neither it opens the drawer nor it closes it when it's open.

Please guide me. Thanks in advance.