如何在dart flutter中从statefulwidget类变为state类？

Question

这是我的扑动代码

import 'package:flutter/material.dart';

class Navbar extends StatefulWidget {
  int tabIndex;
  Navbar(this.tabIndex);

  _NavbarState createState() => _NavbarState();
}

class _NavbarState extends State<Navbar> with SingleTickerProviderStateMixin {
// I need to get tabIndex here
}

我需要在第二堂课中获得tabIndex，非常感谢你的答案