我认为错误来自displayBackground（）方法。我最近更改了代码，以从“ sunrise_sunset.dart”包中获取日出和日落。在此之前，我已经硬编码了日出和日落时间。
displayBackground（）-这将根据当前时间更改背景图像。
import 'pa
ckage:flutter/material.dart';
import 'package:intl/intl.dart';
import 'GetLocation.dart';
import 'package:http/http.dart' as http;
import 'dart:convert';
import 'package:sunrise_sunset/sunrise_sunset.dart';
void main() => runApp(WeatherApp());
class WeatherApp extends StatefulWidget {
@override
_WeatherAppState createState() => _WeatherAppState();
}
class _WeatherAppState extends State<WeatherApp> {
var apiKey = '5f10958d807d5c7e333ec2e54c4a5b16';
var description;
var temp;
var city;
var sunrise;
var sunRise;
var sunSet;
var sunRiseEnd;
var sunSetEnd;
var formattedSunRise;
var formattedSunSet;
var newsunRiseEnd;
var newsunSetEnd;
var sunRise_sunSet_time;
@override
Widget build(BuildContext context) {
return MaterialApp(
home: Container(
decoration: BoxDecoration(
image: DecorationImage(
image: AssetImage(displayBackground()),
),
),
child: Scaffold(
backgroundColor: Colors.transparent,
body: Column(
children: <Widget>[
Container(
margin: EdgeInsets.only(top: 80),
child: Text(
'Your Location',
style: TextStyle(fontSize: 20, color: Colors.white),
),
),
Container(
color: Colors.transparent,
margin: EdgeInsets.symmetric(horizontal: 50),
child: Row(
children: <Widget>[
Container(
child: Text(
'${city.toString()}',
style: TextStyle(fontSize: 30, color: Colors.white),
),
),
SizedBox(width: 50),
Container(
child: Padding(
padding: const EdgeInsets.all(16.0),
child: Icon(
Icons.location_on,
color: Colors.white,
),
),
),
],
),
),
Card(
color: Colors.transparent,
child: Padding(
padding: const EdgeInsets.all(8.0),
child: ListTile(
leading: Padding(
padding: const EdgeInsets.all(8.0),
child: Icon(
Icons.wb_sunny,
color: Colors.white,
),
),
title: Center(
child: Text(
'$temp',
style: TextStyle(fontSize: 20, color: Colors.white),
),
),
subtitle: Center(
child: Text(
'$description',
style: TextStyle(color: Colors.white),
),
),
),
),
),
Container(
child: Center(
child: FlatButton(
child: Text(
'Get Weather Info',
style: TextStyle(color: Colors.white),
),
color: Colors.blueGrey,
onPressed: () {
setState(() {
getLocation();
});
}),
),
),
],
),
),
),
);
}
// display background images based on current time
displayBackground() {
var now = DateTime.now();
print('im here...$formattedSunRise');
print(formattedSunSet);
if ((now.isAfter(sunRise)) || (now.isBefore(sunRiseEnd))) {
return 'images/Moon.png';
} else if ((now.isAfter(sunRiseEnd)) || (now.isBefore(sunSet))) {
return 'images/Sun.png';
} else if ((now.isAfter(sunSet)) || (now.isBefore(sunSetEnd))) {
return 'images/Moon.png';
} else if ((now.isAfter(sunSetEnd)) || (now.isBefore(sunRise))) {
return 'images/Blood.png';
}
return null;
}
//get location
void getLocation() async {
Getlocation getlocation = Getlocation();
await getlocation.getCurrentLocation();
print(getlocation.latitude);
print(getlocation.longitude);
print(getlocation.city);
city = getlocation.city;
getTemp(getlocation.latitude, getlocation.longitude);
}
//Get current temp
Future<void> getTemp(double lat, double lon) async {
http.Response response = await http.get(
'https://api.openweathermap.org/data/2.5/weather?lat=$lat&lon=$lon&appid=$apiKey&units=metric');
// print(response.body);
sunRise_sunSet_time = await SunriseSunset.getResults(
date: DateTime.now(), latitude: lat, longitude: lon);
sunRise = sunRise_sunSet_time.data.sunrise;
sunSet = sunRise_sunSet_time.data.sunset;
formattedSunRise = DateFormat.Hm().format(sunRise);
formattedSunSet = DateFormat.Hm().format(sunSet);
sunRiseEnd = sunRise.add(new Duration(hours: 1));
sunSetEnd = sunSet.add(new Duration(hours: 1));
var dataDecoded = jsonDecode(response.body);
setState(() {
description = dataDecoded['weather'][0]['description'];
temp = dataDecoded['main']['temp'];
sunrise = dataDecoded['sys']['sunrise'];
});
print(temp);
print(sunrise);
}
}
错误：
Performing hot reload...
Syncing files to device Android SDK built for x86...
I/flutter ( 9310): im here...null
I/flutter ( 9310): null
════════ Exception caught by widgets library ═══════════════════════════════════════════════════════
The following NoSuchMethodError was thrown building WeatherApp(dirty, state: _WeatherAppState#c4248):
The getter 'microsecondsSinceEpoch' was called on null.
Receiver: null
Tried calling: microsecondsSinceEpoch
The relevant error-causing widget was:
WeatherApp file:///C:/Users/aldo0/Desktop/Learn_Flutter/my_weather_app/lib/main.dart:8:23
When the exception was thrown, this was the stack:
#0 Object.noSuchMethod (dart:core-patch/object_patch.dart:53:5)
#1 DateTime.isAfter (dart:core-patch/date_patch.dart:87:50)
#2 _WeatherAppState.displayBackground (package:com/main.dart:135:15)
#3 _WeatherAppState.build (package:com/main.dart:40:31)
#4 StatefulElement.build (package:flutter/src/widgets/framework.dart:4619:28)
...
════════════════════════════════════════════════════════════════════════════════════════════════════
Reloaded 1 of 626 libraries in 383ms.
这里您正在发生错误
var dataDecoded = jsonDecode(response.body);
最有可能您的响应类型是字符串。
displayBackground功能不应为async。异步函数返回Future。通过不指定返回类型，它假定函数将返回Future<dynamic>。
将功能更改为此：
String displayBackground() {
var now = DateTime.now();
print('im here...$formattedSunRise');
print(formattedSunSet);
if ( (now.isAfter(sunRise)) || (now.isBefore(sunRiseEnd)) ){
return 'images/Moon.png';
} else if((now.isAfter(sunRiseEnd)) || (now.isBefore(sunSet))){
return 'images/Sun.png';
} else if((now.isAfter(sunSet)) || (now.isBefore(sunSetEnd))){
return 'images/Moon.png';
} else if((now.isAfter(sunSetEnd)) || (now.isBefore(sunRise))){
return 'images/Blood.png';
}
return null; // default return statement
}