隐藏导航栏

    /**
     * 隐藏虚拟按键，并且全屏
     */
    public static void hideBottomNav(Activity activity) {
       View decorView = activity.getWindow().getDecorView();
        decorView.setSystemUiVisibility(0);
        int uiOptions = View.SYSTEM_UI_FLAG_HIDE_NAVIGATION
                | View.SYSTEM_UI_FLAG_IMMERSIVE_STICKY | View.SYSTEM_UI_FLAG_FULLSCREEN | 
        View.SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN;
        decorView.setSystemUiVisibility(uiOptions);
    }

显示导航栏

     /**
      * 重新显示导航栏和状态栏
      */
    public static void showBottomNav(Activity activity) {
       View decorView = activity.getWindow().getDecorView();
        decorView.setSystemUiVisibility(0);
    }

沉浸式状态下显示导航栏

     /**
      *沉浸式全屏状态下，显示导航栏和状态栏
      */
    public static void showBottomNav(Activity activity) {
       View decorView = activity.getWindow().getDecorView();
        decorView.setSystemUiVisibility(0);
        decorView .setSystemUiVisibility(View.SYSTEM_UI_FLAG_LAYOUT_STABLE | 
        View.SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN);
    }