dart - 如何在 flutter 中获取下拉按钮的选定索引

Question

如何在flutter中获取下拉列表的selectedIndex，

在下拉按钮中没有获取选定索引的属性，如果有如何获取选定索引，我的代码如下所示:

new DropdownButton( hint:new Text("Select a users"),value: selectedUser,

              onChanged: (String newValue) {
                setState(() {
                  selectedUser = newValue;
                });
              },
              items: userInfoToMap.map((ListOfUsers value) {
                return new DropdownMenuItem<String>(
                    value: value.name,
                    child:new Text(value.name,style: new TextStyle(color: Colors.black))
                );
              })
                  .toList(),
            ),

          ),),

Answer 1

您可能应该使用自定义模型对象(例如 User)作为 DropdownButton 的类型。

import 'package:flutter/material.dart';

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

class User {
  const User(this.name);    
  final String name;
}

class MyApp extends StatefulWidget {
  State createState() => new MyAppState();
}

class MyAppState extends State<MyApp> {
  User selectedUser;
  List<User> users = <User>[User('Foo'), User('Bar')];    
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      home: new Scaffold(
        body: new Center(
          child: new DropdownButton<User>(
            hint: new Text("Select a user"),
            value: selectedUser,
            onChanged: (User newValue) {
              setState(() {
                selectedUser = newValue;
              });
            },
            items: users.map((User user) {
              return new DropdownMenuItem<User>(
                value: user,
                child: new Text(
                  user.name,
                  style: new TextStyle(color: Colors.black),
                ),
              );
            }).toList(),
          ),
        ),
      ),
    );
  }
}