如何在 Flutter 中过滤 Future 列表？

Question

我需要有关筛选列表的帮助。

我在 initState 中填充列表：

  Future _organisations;

  Future<void> readJson() async {
    final String response =
        await rootBundle.loadString('assets/organisations.json');
    final data = await json.decode(response);

    List<Organization> temp = [];

    for (var item in data) {
      Organization place = Organization(
        address: item['Address'],
        contactInfo: item['Contact info'],
        organization: item['Organization'],
        phoneNumber: item['Phone number'],
        shortDescription: item['Short description'],
        subject: item['Subject'],
        tags: item['Tags'],
      );

      temp.add(place);
    }

    temp.sort((a, b) => a.organization.compareTo(b.organization));

    return temp;
  }

  @override
  void initState() {
    super.initState();
    _organisations = readJson();
  }

然后我在列表上方有一个按钮，我想用它来使用 setState 过滤列表，但是它不起作用。如何过滤 Future 类型的列表？

Answer 1

首先你的方法 readJson() 有一个 return 类型的值 Future<void> 这意味着你将永远无法得到你的 List<Organization> return编辑

此外，您正在使用异步操作，这意味着您需要使用 await 或 then 来在某些时候获取您的值。

这是一个如何修复代码的示例：

List<Organization> _organisations;

// Simply change the return type to Future<List<Organization>>
Future<List<Organization>> readJson() async {
  final String response =
    await rootBundle.loadString('assets/organisations.json');
  final data = await json.decode(response);

  List<Organization> temp = [];

  for (var item in data) {
    Organization place = Organization(
      address: item['Address'],
      contactInfo: item['Contact info'],
      organization: item['Organization'],
      phoneNumber: item['Phone number'],
      shortDescription: item['Short description'],
      subject: item['Subject'],
      tags: item['Tags'],
    );
    temp.add(place);
  }

  /// Then you need to compare objects that are comparable.
  /// For example if you want to sort your items by their address :
  temp.sort((a, b) =>
    a.address.toLowerCase().compareTo(b.address.toLowerCase())
  );

  return temp;
}

@override
void initState() {
  super.initState();
  
  /// As you cannot use await in initState you can use then
  /// to perform an action once your asynchronous operation is
  /// done.
  ///
  /// In this case I am assigning the value to _organisations
  /// and causing a rebuild of the interface with setState.
  readJson().then((List<Organization> temp) {
    setState(() => _organisations = temp);
  });
}

Answer 2

Future<void> 没有 return 任何东西。如果你想让它成为 return 列表，它应该是 Future<List>。当您对列表中的项目进行排序时，您将它们与什么进行比较？项目[“组织”]是什么类型的？它需要是可比较的类型。

如何在 Flutter 中过滤 Future 列表？

How to filter Future List in Flutter?

future

list

filter

dart

flutter