类型"未来"<dynamic>不是类型"列表"的子类型<Application>？

Question

我正试图在flutter中创建一个搜索小部件，对于列表，我使用了device_apps的应用程序列表(https://pub.dev/packages/device_apps)。但是我犯了一个错误；类型"Future"不是类型"List？"的子类型&"。为了创建搜索小部件，我使用了这个链接的帮助。

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功能同步。

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

我认为您需要在调用future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;

}