'Future<dynamic>' 类型不是 'List<Application>?' 类型的子类型

Question

我正在尝试在颤振中创建一个搜索小部件，对于列表，我使用了 device_apps (https://pub.dev/packages/device_apps) 的应用程序列表。但我得到一个错误“类型'未来'不是类型'列表的子类型？'”。为了创建搜索小部件，我使用了来自 this link 的帮助。

这是我的代码：

import 'dart:async';

import 'package:device_apps/device_apps.dart';
import 'package:flutter/material.dart';


class SearchWidget extends StatelessWidget {
  SearchWidget({Key key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return SingleChildScrollView(
      child: Column(
        children: <Widget>[
          TextField(onChanged: _filter),
          StreamBuilder<List<Application>>(
            initialData: lelist(),
            stream: _stream,
            builder:
                    (BuildContext context, AsyncSnapshot<List<Application>> snapshot) {
                  print(snapshot.data);
                  return ListView.builder(
                    shrinkWrap: true,
                    itemCount: snapshot.data.length,
                    itemBuilder: (BuildContext context, int index) {
                      return Text(snapshot.data[index].appName);
                    },
                  );
                },
              )


        ],
      ),
    );
  }
}

StreamController<List<Application>> _streamController = StreamController<List<Application>>();
Stream<List<Application>> get _stream => _streamController.stream;
_filter(String searchQuery) {
  List<Application> _filteredList = lelist()
      .where((Application app) => app.appName.toLowerCase().contains(searchQuery.toLowerCase()))
      .toList();
  _streamController.sink.add(_filteredList);
}

lelist() async {
  List<Application> _dataFromQuerySnapShot = await DeviceApps.getInstalledApplications(includeAppIcons: true);
  _dataFromQuerySnapShot.sort((a, b) {
    return a.appName.toString().toLowerCase().compareTo(b.appName.toString().toLowerCase());
  });
  return _dataFromQuerySnapShot;
}

Answer 1

我认为没有必要在每次击键时加载和排序已安装的应用程序，因此将所有这些逻辑放入 initState。这也使您的 _filter 函数同步。

import 'dart:async';

import 'package:device_apps/device_apps.dart';
import 'package:flutter/material.dart';

class SearchWidget extends StatefulWidget {
  SearchWidget({Key key}) : super(key: key);

  @override
  _SearchWidgetState createState() => _SearchWidgetState();
}

class _SearchWidgetState extends State<SearchWidget> {
  final _streamController = StreamController<List<Application>>();
  List<Application> _dataFromQuerySnapShot;

  Stream<List<Application>> get _stream => _streamController.stream;

  @override
  void initState() {
    DeviceApps.getInstalledApplications(includeAppIcons: true)
        .then((List<Application> apps) {
      _dataFromQuerySnapShot = apps;
      _dataFromQuerySnapShot.sort((a, b) {
        return a.appName
            .toString()
            .toLowerCase()
            .compareTo(b.appName.toString().toLowerCase());
      });
      _streamController.sink.add(_dataFromQuerySnapShot);
    });
    super.initState();
  }

  @override
  void dispose() {
    _streamController.close();
    super.dispose();
  }

  _filter(String searchQuery) {
    final filteredApplications = _dataFromQuerySnapShot
        .where((Application app) =>
            app.appName.toLowerCase().contains(searchQuery.toLowerCase()))
        .toList();
    _streamController.sink.add(filteredApplications);
  }

  @override
  Widget build(BuildContext context) {
    return SingleChildScrollView(
      child: Column(
        children: <Widget>[
          TextField(onChanged: _filter),
          StreamBuilder<List<Application>>(
            stream: _stream,
            builder: (BuildContext context,
                AsyncSnapshot<List<Application>> snapshot) {
              if (!snapshot.hasData) {
                return Center(child: CircularProgressIndicator());
              }
              return snapshot.data.isEmpty
                  ? Center(child: Text('Empty'))
                  : ListView.builder(
                      shrinkWrap: true,
                      itemCount: snapshot.data.length,
                      itemBuilder: (BuildContext context, int index) {
                        return Text(snapshot.data[index].appName);
                      },
                    );
            },
          )
        ],
      ),
    );
  }
}

Answer 2

我认为你需要在调用你的未来之后添加 asList。

lelist() async {
 List<Application> _dataFromQuerySnapShot = await 
   DeviceApps.getInstalledApplications(includeAppIcons: true);
    _dataFromQuerySnapShot.sort((a, b) {
    return 
    a.appName.toString().toLowerCase().compareTo(b.appName.toString().toLowerCase());
 }) as List;
 return _dataFromQuerySnapShot;

}