DartPad -如何为切换标签时移动的TabBar创建自定义指示器-我有一个Flutter示例

import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: DefaultTabController(
        length: 3,
        child: Scaffold(
          appBar: AppBar(
            bottom: TabBar(
              tabs: [
                Tab(icon: Icon(Icons.directions_car)),
                Tab(icon: Icon(Icons.directions_transit)),
                Tab(icon: Icon(Icons.directions_bike)),
              ],
              indicator: BoxDecoration(
                color: Colors.blue,
                borderRadius: BorderRadius.circular(5.0),
              ),
              indicatorSize: IndicatorSize.tab,
            ),
          ),
          body: TabBarView(
            children: [
              Center(child: Text('Cars')),
              Center(child: Text('Transit')),
              Center(child: Text('Bikes')),
            ],
          ),
        ),
      ),
    );
  }
}