Flutter 中带有未来构建器的可重新排序的 ListView

Question

我正在尝试将 Reorderable ListView 实现到 FutureBuilder 中，但目前我运行遇到错误并且不知道这意味着什么。我未来的小部件 'WidgetLook' 已经分配了一个键。

这是我的 Future Builder 代码：

child: FutureBuilder(
  future: getClassList(),
  builder: (BuildContext context, AsyncSnapshot<List> snapchot) {
    if (snapchot.hasData) {
      return ReorderableListView(
        onReorder: _onReorder,
        children: getList(snapchot.data),
      );
    } else
      return CircularProgressIndicator();
  }
)

“getClassList”函数如下所示：

Future<List> getClassList() async {
  final response = await http.get('http://.../classtitle');
  final decoded = json.decode(response.body) as Map<String, dynamic>;
  List classtitlesList = decoded['ClassTitles'];
  return classtitlesList;
}

“getList”函数如下所示：

List<Widget> getList(text) {
  list = [];
  for (int i = 0; i < text.length; i++) {
    list.add(WidgetLook(title: text[i], number: i));
  }
  return list;
}

Widget 本身是这样的：

class WidgetLook extends StatelessWidget {
  final String title;
  final number;
  WidgetLook({this.title, this.number});
  @override
  Widget build(BuildContext context) {
    return GestureDetector(
      key: ValueKey(title),
      onTap: () async {...
      },
      child: Container(...
        child: Align(...
        ),
      ),
    );
  }
}

报错信息是这样的：

All children of this widget must have a key.
'package:flutter/src/material/reorderable_list.dart':
Failed assertion: line 75 pos 10: 'children.every((Widget w) => w.key != null)'

The relevant error-causing widget was
FutureBuilder<List<dynamic>>

为什么会出现此错误，因为我已经为我的小部件分配了一个密钥？

Answer 1

您需要为小部件列表中的项目添加一个键。所以你应该在你的小部件中添加密钥：

class WidgetLook extends StatelessWidget {
  final String title;
  final number;

  const WidgetLook({Key key, this.title, this.number}) : super(key: key);
  
  @override
  Widget build(BuildContext context) {
    return GestureDetector(
      key: ValueKey(title),
      onTap: () async {
      },
      child: Container(
      child: Align(
      ),
    ),
    );
  }
}

现在您应该将键值添加到列表中的小部件：

List<Widget> getList(text) {
  list = [];
  for (int i = 0; i < text.length; i++) {
    list.add(WidgetLook(key: ValueKey(i), title: text[i], number: i));
  }
  return list;
}

Flutter 中带有未来构建器的可重新排序的 ListView

Reorderable ListView with future builder in Flutter

flutter

dart

flutter-listview

flutter-futurebuilder