Toolbar NavigationIcon正确的使用姿势

转一篇文章，非常有用

Toolbar里左侧收缩菜单的NavigationIcon更换步骤很奇怪，一不小心就会失效，只有按照固定步骤才能修改成功

Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);
    drawer = (DrawerLayout)findViewById(R.id.drawer_layout);
    ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
            this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
    drawer.setDrawerListener(toggle);
    toggle.syncState();
    toolbar.setNavigationIcon(R.mipmap.nav_bar_menu);