这适用于DropdownButtonHideUnderline,但不适用于DropdownButtonFormField。我想要通过DropdownButtonFormField获得的inputDecoration,但是当我更改项目时此代码在运行时失败。
This works with DropdownButtonHideUnderline, but does not work with DropdownButtonFormField. I want the inputDecoration that I get with DropdownButtonFormField, but this code fails at runtime when I change the project.
我需要修复它以便与DropdownButtonFormField一起运行,或者我应该找到一种方法得到inputDecoration添加到DropdownButtonHideUnderline;
I either need to fix it to run with DropdownButtonFormField or I should find a way to get the inputDecoration added to the DropdownButtonHideUnderline;
在运行时出现的错误是:
At runtime the error that comes out is:
Either zero or 2 or more [DropdownMenuItem]s were detected with the same value 'package:flutter/src/material/dropdown.dart': Failed assertion: line 827 pos 15: 'items == null || items.isEmpty || value == null || items.where((DropdownMenuItem<T> item) { return item.value == value; }).length == 1'import 'package:flutter/material.dart'; void main() { runApp(MyApp()); } class MyApp extends StatelessWidget { @override Widget build(BuildContext context) { return MaterialApp( title: 'Flutter Demo', theme: ThemeData( primarySwatch: Colors.blue, visualDensity: VisualDensity.adaptivePlatformDensity, ), home: MyHomePage(title: 'Flutter Demo Home Page'), ); } } class MyHomePage extends StatefulWidget { MyHomePage({Key key, this.title}) : super(key: key); final String title; @override _MyHomePageState createState() => _MyHomePageState(); } Map data = { 'Project 1': ['Entrance', 'Main Hallway', 'Kitchen'], 'Project 2': ['Patio', 'Dining Room'], }; class _MyHomePageState extends State<MyHomePage> { String _project; String _room; List<String> _roomList = []; @override Widget build(BuildContext context) { return Scaffold( appBar: AppBar( title: Text(widget.title), ), body: Center( child: Column( children: <Widget>[ DropdownButtonFormField( decoration: InputDecoration(labelText: 'Project'), value: _project, onChanged: (value) { setState(() { _project = value; _room = null; _roomList = data[_project]; }); }, items: data.keys.map((item) { return DropdownMenuItem( child: Text(item), value: item, ); })?.toList() ?? [], ), DropdownButtonFormField( decoration: InputDecoration(labelText: 'Room'), value: _room, onChanged: (value) { setState(() { _room = value; print(_project); print(_room); }); }, items: _roomList.map((item) { return DropdownMenuItem( child: Text(item), value: item, ); })?.toList() ?? [], ), ], ), )); } }
推荐答案
您可以在 下面复制粘贴运行完整代码 当下拉列表数据完全不同时,将触发此错误 对于房间 DropdownButtonFormField 您可以使用 key:UniqueKey(),小部件将重新创建
You can copy paste run full code below When Dropdown list data is totally different will trigger this error For Room DropdownButtonFormField You can use key: UniqueKey() and widget will recreate
代码段
DropdownButtonFormField( key: UniqueKey(), decoration: InputDecoration(labelText: 'Room'),工作演示
完整代码
import 'package:flutter/material.dart'; void main() { runApp(MyApp()); } class MyApp extends StatelessWidget { @override Widget build(BuildContext context) { return MaterialApp( title: 'Flutter Demo', theme: ThemeData( primarySwatch: Colors.blue, visualDensity: VisualDensity.adaptivePlatformDensity, ), home: MyHomePage(title: 'Flutter Demo Home Page'), ); } } class MyHomePage extends StatefulWidget { MyHomePage({Key key, this.title}) : super(key: key); final String title; @override _MyHomePageState createState() => _MyHomePageState(); } Map data = { 'Project 1': ['Entrance', 'Main Hallway', 'Kitchen'], 'Project 2': ['Patio', 'Dining Room'], }; class _MyHomePageState extends State<MyHomePage> { String _project; String _room; List<String> _roomList = []; @override Widget build(BuildContext context) { return Scaffold( appBar: AppBar( title: Text(widget.title), ), body: Center( child: Column( children: <Widget>[ DropdownButtonFormField( decoration: InputDecoration(labelText: 'Project'), value: _project, onChanged: (value) { setState(() { _project = value; _room = null; _roomList = data[_project]; }); }, items: data.keys.map((item) { return DropdownMenuItem( child: Text(item), value: item, ); })?.toList() ?? [], ), DropdownButtonFormField( key: UniqueKey(), decoration: InputDecoration(labelText: 'Room'), value: _room, onChanged: (value) { setState(() { _room = value; print(_project); print(_room); }); }, items: _roomList.map((item) { return DropdownMenuItem( child: Text(item), value: item, ); })?.toList() ?? [], ), ], ), )); } }更多推荐
DropdownButtonFormField断言在DropdownButtonHideUnderline不存在的地方失败
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