如何使用Riverpod Notifier创建drowdownbutton按钮？

Question

我想在Riverpod中用changenotifierProvider创建DropDownButton，但是我不能很好地编写我的代码。请帮帮我。我想，我只是写了“watch”方法，但我不知道如何阅读它。所以，它应该显示所选择的项目，也应该是与provider.Category更新。

我的DropDownButton代码如下：

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

这是我的DropDownButton图像：(当我选择列表中的任何项目时，它都不能正常工作。它总是选择第一个(它选择“英雄联盟”)。

​

我选择steam但卡片目录显示为英雄联盟

​

Answer 1

final postProvider =
    ChangeNotifierProvider<PostProvider>((ref) => PostProvider());

class PostProvider extends ChangeNotifier {
  String _postCategory;

  String get postCategory => _postCategory;

  categoryOnChanged(String value) {
    if (value.isEmpty) {
      return _postCategory;
    }
    _postCategory = value;
    print(_postCategory);
    return notifyListeners();
  }
}

class DropDownPage extends StatefulWidget {
  @override
  _DropDownPageState createState() => _DropDownPageState();
}

class _DropDownPageState extends State<DropDownPage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("Dropdown Riverpod issue"),
      ),
      body: Container(
        height: MediaQuery.of(context).size.height,
        width: MediaQuery.of(context).size.width,
        child: Center(
          child: _DropDownWidgetConsumer(),
        ),
      ),
    );
  }
}

class _DropDownWidgetConsumer extends ConsumerWidget {
  @override
  Widget build(BuildContext context, ScopedReader watch) {
    final category = watch(postProvider).postCategory;
    return DropdownButton(
      hint: Text("Choose category"),
      value: category,
      items: <String>["League Of Legends", "Steam", "Csgo"]
          .map((e) => DropdownMenuItem<String>(
        
                onTap: () => e,
                value: e ?? category,
                child: Text(e ?? "$category"),
              ))
          .toList(),
      onChanged: (value) {
        context.read(postProvider).categoryOnChanged(value);
      },
    );
  }
}