Flutter：setState((){} 无法重绘 DropdownButton 值

Question

我是 Flutter 新手，正在尝试编写手机游戏代码。到目前为止，我已经能够通过论坛、youtube 教程和示例应用程序上的先前问题进行管理。但是我遇到了我无法解决的墙。

我的 UI 中的许多功能都应该根据用户行为进行更改，但不会更新，我使用此 DropdownButton 作为示例，但这也是我在代码中其他地方遇到的问题。当用户从 DropdownButton 进行选择时，它应该更新按钮的值，但只显示提示。我已经能够通过打印语句确定选择已注册。

根据我目前所了解的情况，我怀疑这个问题与我的小部件的状态或缺乏状态有关。我发现了一些类似的问题，建议使用 StatefulBuilder，但是当我尝试实现它时，代码有错误，或者重复了我的整个 ListTile 组。我还看到了有关创建有状态小部件的建议，但这些说明对我来说太模糊了，无法毫无错误地遵循和实施。我包括下面代码的 sn-ps，我犹豫要粘贴整个内容，因为此时该应用程序将近 2000 行。如果需要任何进一步的信息或代码，请告诉我。 这是有问题的代码，请参阅下面的上下文代码。

        DropdownButton(
          value: skillChoice,
          items: listDrop,
          hint: Text("Choose Skill"),
          onChanged: (value) {
            setState(() {
              skillChoice = value;
            });
          },
        ),

void main() => runApp(MyApp());
class MyApp extends StatelessWidget {

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Hunters Guild',
      theme: ThemeData(
        primaryColor: Colors.grey,
      ),
      home: Main(),
    );
  }
}
final List<Combatant> _combatants = List<Combatant>(); 
//combatant is a class that holds stats like HP which may change during a battle
//they also have a Fighter and a Monster and one of those will be null and the other useful
//depending if faction = "good" or "evil
//I am aware that this may not be the most elegant implementation but that is a problem for another day.

class MainState extends State<Main> {
  final List<Fighter> _squad = List<Fighter>(); 
//Fighter is a class which stores info like HP, name, skills, etc for game character,
//this List is populated in the page previous to _fight 
//where the user picks which characters they are using in a given battle
void _fight(Quest theQuest){
    for(Fighter guy in _squad){
      _combatants.add(Combatant("good", guy, null));
    }
    _combatants.add(Combatant("evil", null, theQuest.boss)); 
//quests are a class which store a boss Monster, later on I will add other things like rewards and prerequisites
final tiles = _combatants.map((Combatant comba){ //this structure is from the build your first app codelab
      List<DropdownMenuItem<String>> listDrop = [];
      String skillChoice = null;
      if (comba.faction == "good"){
        for (Skill skill in comba.guy.skills){
          listDrop.add((DropdownMenuItem(child: Text(skill.name), value: skill.name)));
        }
      }
      else if (comba.faction == "evil"){
        for (Skill skill in comba.boss.skills){
          listDrop.add((DropdownMenuItem(child: Text(skill.name), value: skill.name)));
        }
      }
//^this code populates each ListTile (one for each combatant) with a drop down button of all their combat skills
      return ListTile(

        leading: comba.port,
        title: Text(comba.info),
        onTap: () {
          if(comba.faction == "good"){
            _fighterFightInfo(comba.guy, theQuest.boss); //separate page with more detailed info, not finished
          }
          else{
            _monsterFightInfo(theQuest.boss); //same but for monsters
          }
        },
        trailing: Row(
          mainAxisSize: MainAxisSize.min,
          children: [

            DropdownButton( //HERE IS WHERE THE ERROR LIES
              value: skillChoice,
              items: listDrop,
              hint: Text("Choose Skill"),
              onChanged: (value) {
                setState(() {
                  skillChoice = value;
                });
              },
            ),
            IconButton(icon: Icon(Icons.check), onPressed: (){
//eventually this button will be used to execute the user's skill choice
            })
          ],
        ),
        subtitle: Text(comba.hp.toString()),
      );
    },
    );
    Navigator.of(context).push(
      MaterialPageRoute<void>(
        builder: (BuildContext context) {
//I have tried moving most of the above code into here, 
//and also implementing StatelessBuilders here and other places in the below code to no effect
          final divided = ListTile.divideTiles(
            context: context,
            tiles: tiles,
          ).toList();
          return Scaffold(
            appBar: AppBar(
              title: Text("Slay "+theQuest.boss.name+"  "+theQuest.boss.level.toString()+"  "+theQuest.boss.type.name, style: TextStyle(fontSize: 14),),
              leading: IconButton(icon: Icon(Icons.arrow_back), onPressed: () {
                _squadSelect(theQuest);
              }),
            ),
            body: ListView(children: divided),
          );
        },
      ),
    );
  }
//there are a lot more methods here which I haven't included
 @override

  Widget build(BuildContext context) {
//I can show this if you need it but there's a lot of UI building on the main page
//Also might not be the most efficiently implemented
//what you need to know is that there are buttons which call _fight and go to that page
}
class Main extends StatefulWidget {
  @override
  MainState createState() => MainState();
}

感谢您提供的任何帮助或建议。

Answer 1

有点难以理解这里发生了什么，所以如果可能的话，将问题区域添加到一个新的小部件中并将其发布在这里。

无论如何，目前看来您的 SkillShare 变量是本地的，因此每次设置状态时它都不会更新。试试这样的：

class MainState extends State<Main> {
String skillShare = ""; //i.e make skillShare a global variable
final List<Fighter> _squad = List<Fighter>(); 

Answer 2

以下问题提供了帮助我找到答案的信息。不同的问题，但解决方案适用。感谢用户：4576996 斯文。基本上我需要从在 void _fight 中进行构建重新格式化为新的有状态页面。这对于使用入门教程作为框架来构建他们的应用程序的其他人可能很有用。

flutter delete item from listview