我在州管理领域完全迷失了。尝试了多个教程，文章，甚至查看了Github的类似项目。不知道如何在我的Weather应用中实现提供商。
class WeatherMainScreen extends StatelessWidget {
@override
Widget build(BuildContext context) {
return Container(
color: kBackgroundColor,
child: SafeArea(
child: ChangeNotifierProvider<WeatherModel>(
create: (context) => ApiCall().getWeather('New York'),
child: Column(
mainAxisAlignment: MainAxisAlignment.spaceBetween,
children: <Widget>[
Container(
margin: EdgeInsets.only(
bottom: 30,
top: 15,
left: 30,
right: 30,
),
child: Column(
children: <Widget>[
Row(
mainAxisAlignment: MainAxisAlignment.spaceBetween,
children: <Widget>[
Text(
'Today 28. apr',
style: TextStyle(
color: kAccentColor,
fontSize: 18,
fontWeight: FontWeight.w400,
),
),
Row(
mainAxisAlignment: MainAxisAlignment.end,
children: <Widget>[
MenuSearchButton(
boxSize: 60,
onPressed: () => print('search prssed'),
content: Icon(
Icons.search,
color: Colors.white,
size: 30,
),
),
MenuSearchButton(
boxSize: 60,
onPressed: () => print('menu pressed'),
content: Icon(
Icons.menu,
color: Colors.white,
size: 30,
),
),
],
),
],
),
Container(
padding: EdgeInsets.symmetric(vertical: 20.0),
child: Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: <Widget>[
Text(
'12',
style: TextStyle(
color: Colors.white,
fontSize: 100,
),
),
Container(
padding: EdgeInsets.only(left: 10.0),
child: Row(
children: <Widget>[
Icon(
Icons.cloud,
color: Colors.white,
size: 25.0,
),
SizedBox(width: 15.0),
Text(
'Raining',
style: TextStyle(
color: Colors.white,
fontSize: 18,
),
),
],
),
),
],
),
),
],
),
),
Column(
children: <Widget>[
Container(
margin: EdgeInsets.only(
bottom: 30,
top: 15,
left: 60,
right: 60,
),
child: Text(
'Put on your coat, and don\'t forget the umbrella.',
textAlign: TextAlign.center,
style: TextStyle(
color: Colors.white,
fontSize: 25,
),
),
),
Divider(
color: kAccentColor,
),
Container(
margin: EdgeInsets.only(
bottom: 30,
top: 15,
left: 30,
right: 30,
),
child: Row(
mainAxisAlignment: MainAxisAlignment.spaceEvenly,
children: <Widget>[
DetailedCard(
header: 'HUMIDITY',
headerColor: kAccentColor,
text: '87%',
textColor: Colors.white,
),
DetailedCard(
header: 'WIND M/S',
headerColor: kAccentColor,
text: '4,1',
textColor: Colors.white,
),
DetailedCard(
header: 'FEELS LIKE',
headerColor: kAccentColor,
text: '18',
textColor: Colors.white,
),
],
),
),
],
),
],
),
),
),
);
}
}
所以我有一个模型类WeatherModel，它基本上是空的，仅包含天气信息的构造函数。 ApiCall类是所有联网的地方，它返回填充了数据的WeatherModel对象。但是使用这样的ChangeNotifier我得到了错误： “返回类型'Future'不是由匿名闭包定义的'WeatherModel'。
我读到ChangeNotifierProvider应该在创建时只接收一个Object，而我正在传递给它一个函数。但是我不知道该在哪里调用getWeather函数？完全迷路了。
编辑：
ApiCall.dart
class ApiCall extends ChangeNotifier{
Future<WeatherModel> getWeather(String cityName) async {
String url =
'https://api.openweathermap.org/data/2.5/weather?q=$cityName&appid=$apikey';
http.Response response = await http.get(url);
if (response.statusCode == 200) {
var weatherData = jsonDecode(response.body);
return WeatherModel(
temp: weatherData['main']['temp'] - 273.15,
feelsLike: weatherData['main']['temp'] - 273.15,
condition: weatherData['weather'][0]['main'],
humidity: weatherData['main']['humidity'],
windSpeed: weatherData['wind']['speed'],
);
} else {
throw Exception('Ooops something went wrong');
}
}
}
WeatherModel.dart
class WeatherModel{
final double temp;
final double windSpeed;
final int feelsLike;
final int humidity;
final String condition;
WeatherModel({
this.temp,
this.windSpeed,
this.feelsLike,
this.humidity,
this.condition,
});
}
答案 0 :(得分：0)
您应该对代码进行一些更改。
更改下一行
child: ChangeNotifierProvider<WeatherModel>(
收件人
child: ChangeNotifierProvider< ApiCall >(
您必须提供扩展ChangeNotifier的类名。
您必须在方法末尾调用notifyListeners（），要在其上更改数据。
else {
throw Exception('Ooops something went wrong');
}
notifyListeners(); // added line
}
getWeather不应返回任何值。取而代之的是，您可以在ApiCall类中创建任何WeatherModel对象，并在该方法中对其进行更新，并在想要使用该数据的任何位置访问该对象。
更新：
child: ChangeNotifierProvider<ApiCalll>( create: (context) => ApiCall()
您可以通过以下方式调用此方法。
Provider.of<ApiCall>(context).getWeather('New York');