我如何实时查看下拉按钮

问题描述

我的问题是我无法实时看到我选择的实时字符串。 例如，如果我从下拉项目中选择一个字符串，那么我看不到它。如果我想看到它，首先我必须返回并再次打开表格。我该如何解决这个问题？ （顺便说一句，它有效，提交按钮没有问题。我只是想看看用户选择了什么。

我的问题：

我的代码：

Widget dropdownButton(BuildContext context) {
    String constantValue = "League Of Legends";
    return DropdownButton(
        value: context.read<PostProvider>().postCategory ?? constantValue,onChanged: (newValue) {
          context.read<PostProvider>().postCategory = newValue;
     
        },items: <String>["League Of Legends","Steam","Csgo"]
            .map<DropdownMenuItem<String>>((String value) {
          return DropdownMenuItem<String>(
            onTap: () => context.read<PostProvider>().postCategory,value: value,child: Text(value),);
        }).toList());
  }






String get postCategory => _postCategory;

  set postCategory(String value) {
    _postCategory = value;
    notifyListeners();
  }

还有 PostProvider 扩展了 changenotifier:

String get postCategory => _postCategory;

  set postCategory(String value) {
    _postCategory = value;
    notifyListeners();
  }

主页：

Scaffold(
        floatingActionButton: CreatePostButton(),appBar: AppBar(
          title: Row(
            mainAxisAlignment: MainAxisAlignment.spaceBetween,children: [
              Text("Home Page"),IconButton(
                  onpressed: () {
                    provider.logout();
                  },icon: FaIcon(FontAwesomeIcons.poo))
            ],),body: HomePageWidget())

创建帖子按钮：

class CreatePostButton extends StatelessWidget {
  static final _formKey = GlobalKey<FormState>(debugLabel: '_formKey');
  static final _scaffoldKey = GlobalKey<ScaffoldState>();
  @override
  Widget build(BuildContext context) => Padding(
        padding: const EdgeInsets.only(right: 13.0,bottom: 13.0),child: FloatingActionButton(
            child: FaIcon(FontAwesomeIcons.plus),onpressed: () {
              showDialog(context: context,child: builDalertDialog(context));
            }),);

  Widget builDalertDialog(BuildContext context) {
    final provider = Provider.of<PostProvider>(context,listen: false);
    return AlertDialog(
      content: Form(
        key: _formKey,child: SingleChildScrollView(
          child: Column(
            mainAxisSize: MainAxisSize.min,children: <Widget>[
              Padding(
                  padding: EdgeInsets.all(8.0),child: TextFormField(
                      autocorrect: true,textCapitalization: TextCapitalization.words,enableSuggestions: false,validator: (value) {
                        if (value.isEmpty || value.length <= 4) {
                          return 'Please enter at least 4 characters';
                        } else {
                          return null;
                        }
                      },decoration: Inputdecoration(labelText: 'Post Title'),onChanged: (postTitle) {
                        provider.postTitle = postTitle;
                      })),Padding(
                  padding: EdgeInsets.all(8.0),validator: (value) {
                        if (value.isEmpty || value.length <= 25) {
                          return 'Please enter at least 25 characters';
                        } else {
                          return null;
                        }
                      },decoration:
                          Inputdecoration(labelText: 'Write a post details'),onChanged: (postDetails) {
                        provider.postDetails = postDetails;
                      })),child: TextFormField(
                      enableSuggestions: false,inputFormatters: <TextInputFormatter>[
                        FilteringTextInputFormatter.digitsOnly
                      ],keyboardType: TextInputType.number,validator: (value) {
                        if (value.isEmpty || value.length >= 4) {
                          return 'Please enter a valid value';
                        } else {
                          return null;
                        }
                      },decoration: Inputdecoration(labelText: 'Enter the Price'),onChanged: (gamePrice) {
                        provider.gamePrice = gamePrice;
                      })),dropdownButton(context),Padding(
                padding: const EdgeInsets.all(8.0),child: RaisedButton(
                    child: Text("Submit"),onpressed: () => submitNewPost(context)),],);
  }

  Future submitNewPost(BuildContext context) async {
    final provider = Provider.of<PostProvider>(context,listen: false);
    final isValid = _formKey.currentState.validate();
    FocusScope.of(context).unfocus();
    if (isValid) {
      _formKey.currentState.save();

      final isSuccess = await provider.createNewPost();

      if (isSuccess) {
        Navigator.of(context).pop();
      } else {
        final message = 'An error occurred,please check your inputs!';

        Center(child: Text(message),);
      }
    }
  }

  Widget dropdownButton(BuildContext context) {
    String constantValue = "League Of Legends";
    return DropdownButton(
        value: context.read<PostProvider>().postCategory ?? constantValue,);
        }).toList());
  }
}

解决方法

用消费者包装您的下拉按钮以更新小部件：

    Widget dropdownButton(BuildContext context) {
                String constantValue = "League Of Legends";
                
    
       return Consumer<PostProvider>(builder: (_context,_postprovider,_widget) { 
             return DropdownButton(
                    value: _postprovider.postCategory  ?? constantValue,onChanged: (newValue) {
                      _postprovider.postCategory = newValue;
                 
                    },items: <String>["League Of Legends","Steam","Csgo"]
                        .map<DropdownMenuItem<String>>((String value) {
                      return DropdownMenuItem<String>(
                        onTap: () => context.read<PostProvider>().postCategory,value: value ?? constantValue,child: Text(value ?? constantValue),);
                    }).toList());
              });
      }

在这里添加：

 Future submitNewPost(BuildContext context) async {
    final provider = Provider.of<PostProvider>(context,listen: false);
    final isValid = _formKey.currentState.validate();
    FocusScope.of(context).unfocus();
    if (isValid) {
       if( provider.postCategory == null || provider.postCategory.isEmpty){
         provider.postCategory = "League Of Legends";
       } 

      _formKey.currentState.save();

      final isSuccess = await provider.createNewPost();

      if (isSuccess) {
        Navigator.of(context).pop();
      } else {
        final message = 'An error occurred,please check your inputs!';

        Center(child: Text(message),);
      }
    }
  }