Flutter AppBar示例一

import 'package:flutter/material.dart';

class DidiSample extends StatefulWidget{
  @override
  _DidiSampleState createState() => new _DidiSampleState();
}
class _DidiSampleState extends State<DidiSample>{
  Choice _selectedChoice = choices[0];

  void _select(Choice choice){
    setState(() {
      _selectedChoice = choice;
    });
  }

  @override
  Widget build(BuildContext context) {
    // TODO: implement build
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: const Text("滴滴出行"),
          actions: <Widget>[
            IconButton(
              icon: Icon(choices[0].icon),
              onPressed: (){
                _select(choices[0]);
              },
            ),
            IconButton(
              icon: Icon(choices[1].icon),
              onPressed: (){
              _select(choices[1]);
              },
            ),
            PopupMenuButton<Choice>(
              onSelected: _select,
              itemBuilder: (BuildContext context){
                return choices.skip(2).map<PopupMenuItem<Choice>>((Choice choice){
                  return PopupMenuItem<Choice>(
                    value:choice,
                    child: Text(choice.title),
                  );
                }).toList();

              },
            )
          ],
        ),
        body: Padding(
          padding: EdgeInsets.all(20),
          child: ChoiceDidi(choice: _selectedChoice,),
        ),
      ),
    );
  }
}
class Choice{
  final String title;
  final IconData icon;
  const Choice({this.title, this.icon});
}
const List<Choice> choices = <Choice>[
  Choice(title: '自驾', icon:Icons.directions_car),
  Choice(title: '乘般', icon:Icons.directions_boat),
  Choice(title: '自行车',icon: Icons.directions_bike),
  Choice(title: '飞机', icon:Icons.directions_bus),
  Choice(title: '火车', icon:Icons.directions_railway)

];
class ChoiceDidi extends StatelessWidget{
  const ChoiceDidi({Key key, this.choice}):super(key:key);
  final Choice choice;
  @override
  Widget build(BuildContext context) {
    // TODO: implement build
    final TextStyle textStyle = Theme.of(context).textTheme.display1;
    return Center(
      child: Card(
        color: Colors.white,
        child: Column(
          children: <Widget>[
            Icon(choice.icon, size: 128.0, color: textStyle.color,),
            Text(choice.title, style: textStyle,)
          ],
        ),
      ),
    );
  }
}
void main(){
  runApp(DidiSample());
}