DropdownButtonFormField断言在DropdownButtonHideUnderline不存在的地方失败

本文介绍了DropdownButtonFormField断言在DropdownButtonHideUnderline不存在的地方失败的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

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() ?? [], ), ], ), )); } }