在子小部件方法中访问提供程序变量

Question

我正在尝试访问 branchSelected，一个在我的脚手架子窗口小部件中的代码顶部声明的提供程序。当我在原始小部件中使用 branchSelected.branchDropdownValue 时，它起作用了。但是，当我进入子小部件方法时，特别是

ElevatedButton(
        onPressed: () {
          branchSelected.branchChange;
          /*
          refreshBranchData();
          refreshProjectData();
          */
        },
        child: Icon(Icons.refresh))

，我收到错误“未定义名称 'branchSelected'”。查看其他文档，我认为所有的子部件都应该能够访问提供者；但是，这里似乎并非如此。有任何想法吗？我在下面附上了我的代码：

@override
Widget build(BuildContext context) {
final branchSelected = Provider.of<branchListChanges>(context);
return Scaffold(
  appBar: AppBar(
    title: Text('Build Launcher'),
  ),
  body: Padding(
    padding: const EdgeInsets.all(8.0),
    child: Column(
      children: [
        _buildTopRow(),
        Consumer<branchListChanges>(builder: (context, data, child) {
          return Text(
              'Current Branch: ${branchSelected.branchDropdownValue}');
        }),
        _buildList(),
      ],
    ),
  ),
  backgroundColor: Colors.grey[200],
);
}

Expanded _buildList() {
// Sets which branch to view for the list runs

return Expanded(
  child: RunList(branches, "main"),
);
}

Row _buildTopRow() {
return Row(
  children: [
    Text("Project:"),
    SizedBox(width: 6),
    ProjectDropdown(packages),
    SizedBox(width: 6),
    Text("Branch:"),
    SizedBox(width: 6),
    BranchDropdown(branchNames),
    SizedBox(width: 6),
    Checkbox(
      checkColor: Colors.white,
      fillColor: MaterialStateProperty.all<Color>(Colors.blue),
      value: onlyLatestPerDay,
      onChanged: (bool? value) {
        setState(() {
          onlyLatestPerDay = value!;
        });
      },
    ),
    SizedBox(width: 3),
    Text("Only latest per-day"),
    SizedBox(width: 6),
    Checkbox(
      checkColor: Colors.white,
      fillColor: MaterialStateProperty.all<Color>(Colors.blue),
      value: onlyInstalled,
      onChanged: (bool? value) {
        setState(() {
          onlyInstalled = value!;
        });
      },
    ),
    SizedBox(width: 3),
    Text("Only installed"),
    SizedBox(width: 6),
    ElevatedButton(
        onPressed: () {
          branchSelected.branchChange;
          /*
          refreshBranchData();
          refreshProjectData();
          */
        },
        child: Icon(Icons.refresh))
  ],
);
}
}

我在下面的 main.dart 中创建了我的提供商：

class HomePageState extends State<HomePage> {
@override
Widget build(BuildContext context) {
  return MaterialApp(
    title: 'cornerCan',
    theme: ThemeData(
      primarySwatch: Colors.blue,
  ),
  // EFFECTS: runs mainPage function in main_page.dart
  home: ChangeNotifierProvider<branchListChanges>(
    create: (context) => branchListChanges(),
    child: mainPage(),
  ),
);
}
}

Answer 1

您的 branchSelected 变量的范围仅在构建函数内。您需要在构建函数之外声明它才能访问它。
您也可以将其作为参数传递给_buildTopRow()函数例如_buildTopRow(branchSelected)

在子小部件方法中访问提供程序变量

Access Provider variable in child widget methods

flutter

dart