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

Question

我是 Flutter 新手，正在尝试编写手游代码。到目前为止，我已经能够解决之前在论坛、youtube 教程和示例应用程序上提出的问题。但是我遇到了我无法解决的问题。

我的 UI 中的许多功能应该根据用户行为而改变，但不会更新，我使用这个 DropdownButton 作为我的例子，但这是我在代码其他地方遇到的问题出色地。当用户从 DropdownButton 中进行选择时，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有状态性或缺乏状态有关。我发现了一些建议使用 StatefulBuilder 的类似问题，但是当我尝试实现它时，代码有错误或者复制了我的整个 ListTile 组。我还看到了关于创建有状态小部件的建议，但是这些说明太模糊了，我无法遵循和实施而不会出错。我包括下面的代码片段，我犹豫要不要粘贴整个代码，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，将问题区域添加到新的小部件中，然后 post 在此处添加。

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

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

Answer 2

下面的问题有帮助我找到答案的信息。不同的问题，但解决方案适用。谢谢 user:4576996 斯文。基本上我需要重新格式化，从在 void _fight 中构建到一个新的有状态页面。这对于使用入门教程作为框架来构建其应用程序的其他人可能有用。

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

Flutter: setState((){} fails to redraw DropdownButton value

stateful

setstate

dart

flutter