尝试获取并将位置存储在本地数据库中时出现此错误 这是我的主页。飞镖
import 'package:attendance_app/local_database/database_helper.dart';
import 'package:flutter/material.dart';
import 'package:geolocator/geolocator.dart';
import 'package:intl/intl.dart';
import 'package:toast/toast.dart';
import 'package:attendance_app/local_database/database.dart';
class MyHomePage extends StatefulWidget {
MyHomePage({Key key, this.title}) : super(key: key);
final String title;
@override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
bool _buttonEnabled = true;
Position _currentPosition;
String _formattedDate;
DataBaseHelper helper;
@override
void initState() {
// TODO: implement initState
super.initState();
_getCurrentLocation();
}
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text(
widget.title,
style: TextStyle(color: Colors.white),
),
),
body: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Container(
height: 55.0,
width: 150.0,
color: Colors.lightGreen,
child: RaisedButton(
elevation: 0,
textColor: Colors.white,
splashColor: Colors.amber,
disabledColor: Colors.grey,
child: Text(
"Head start",
textScaleFactor: 1.6,
),
color: Colors.lightGreen,
onPressed: () async {
_getCurrentLocation();
_getDateTime();
_insertToDb(createDataBaseObj(
'IN',
_currentPosition.latitude.toString(),
_currentPosition.longitude.toString(),
_formattedDate));
Toast.show("$_currentPosition , $_formattedDate", context,
duration: Toast.LENGTH_LONG, gravity: Toast.BOTTOM);
},
),
),
SizedBox(
height: 20.0,
),
Container(
height: 55.0,
width: 150.0,
color: Colors.red[300],
child: RaisedButton(
elevation: 0,
textColor: Colors.white,
splashColor: Colors.amber,
disabledColor: Colors.grey,
child: Text(
"Check out",
textScaleFactor: 1.6,
),
color: Colors.red[300],
onPressed: () async {
_getCurrentLocation();
_getDateTime();
_insertToDb(createDataBaseObj(
'OUT',
_currentPosition.latitude.toString(),
_currentPosition.longitude.toString(),
_formattedDate));
Toast.show(
"$_currentPosition , $_formattedDate", context,
duration: Toast.LENGTH_LONG, gravity: Toast.BOTTOM);
},
)),
]),
),
bottomNavigationBar: Container(
height: 55.0,
color: _buttonEnabled ? Colors.green : Colors.grey,
child: RaisedButton(
elevation: 0,
textColor: Colors.white,
splashColor: Colors.amber,
disabledColor: Colors.grey,
child: Text(
"sync",
textScaleFactor: 1.6,
),
color: Colors.green,
onPressed: () async {},
)));
}
_getCurrentLocation() async {
final Geolocator geolocator = Geolocator()..forceAndroidLocationManager;
await geolocator
.getCurrentPosition(desiredAccuracy: LocationAccuracy.best)
.then((Position position) {
print(position);
setState(() {
_currentPosition = position;
});
}).catchError((e) {
print(e);
});
}
_getDateTime() {
DateTime now = DateTime.now();
String formattedDate = DateFormat('kk:mm:ss EEE d MMM').format(now);
setState(() {
_formattedDate = formattedDate;
});
}
DataBase createDataBaseObj(type, lat, long, time) {
DataBase result = DataBase(type, lat, long, time);
print('createDataBaseObj');
print(result.toMap());
return result;
}
void _insertToDb(DataBase dataBase) async {
var value = await helper.insertData(dataBase);
print(value);
}
void _delete(BuildContext context, DataBase dataBase) async {
await helper.deleteData(dataBase.id);
}
}
这是database_helper.dart文件
import 'package:sqflite/sqflite.dart';
import 'dart:async';
import 'dart:io';
import 'package:path_provider/path_provider.dart';
import 'database.dart';
class DataBaseHelper {
static DataBaseHelper _dataBaseHelper;
static Database _database;
String table = 'attendance';
String id = 'id';
String type = 'type';
String latitude = 'latitude';
String longitude = 'longitude';
String time = 'time_stamp';
DataBaseHelper._createInstance();
factory DataBaseHelper() {
if (_dataBaseHelper == null) {
_dataBaseHelper = DataBaseHelper._createInstance();
}
return _dataBaseHelper;
}
Future<Database> get database async{
if (_database == null){
_database = await initializeDatabase();
}
return _database;
}
Future<Database> initializeDatabase() async{
Directory directory = await getApplicationDocumentsDirectory();
String path = directory.path + 'attendance.db';
print(path);
var attendanceDb = await openDatabase(path,version: 1,onCreate: _createDb);
return attendanceDb;
}
// Create Table
void _createDb(Database db,int newVersion) async{
await db.execute('CREATE TABLE $table($id INTEGER PRIMARY KEY AUTOINCREMENT, $type TEXT,$latitude TEXT, $longitude TEXT, $time TEXT)');
}
// Fetch data from DB
Future<List<Map<String, String>>> getDatafromdb() async{
Database db = await this.database;
var result = await db.query(this.table);
return result;
}
// Insert data to DB
Future<int> insertData(DataBase dataBase) async{
var db = await this.database;
print('database');
print(db);
var result = await db.insert(this.table, dataBase.toMap());
return result;
}
// Delete data from DB
Future<int> deleteData(int Id) async{
var db = await this.database;
var result = await db.rawDelete('DELETE FROM $table WHERE $id = $Id');
return result;
}
}
错误
An Observatory debugger and profiler on CPH1853 is available at:
http://127.0.0.1:43427/vxgmPQJhR4E=/
For a more detailed help message, press "h". To detach, press "d"; to quit,
press "q".
I/flutter (27382): createDataBaseObj
I/flutter (27382): {type: IN, latitude: 11.1115482, longitude: 77.3637584, timeStamp: 12:09:29 Thu 2 Jan}
E/flutter (27382): [ERROR:flutter/lib/ui/ui_dart_state.cc(157)] Unhandled Exception: NoSuchMethodError: The method 'insertData' was called on null.
E/flutter (27382): Receiver: null
E/flutter (27382): Tried calling: insertData(Instance of 'DataBase')
E/flutter (27382): #0 Object.noSuchMethod (dart:core-patch/object_patch.dart:53:5)
E/flutter (27382): #1 _MyHomePageState._insertToDb (package:attendance_app/screens/homepage.dart:147:30)
E/flutter (27382): #2 _MyHomePageState.build.<anonymous closure> (package:attendance_app/screens/homepage.dart:58:23)
E/flutter (27382): #3 _AsyncAwaitCompleter.start (dart:async-patch/async_patch.dart:45:6)
E/flutter (27382): #4 _MyHomePageState.build.<anonymous closure> (package:attendance_app/screens/homepage.dart:55:32)
E/flutter (27382): #5 _InkResponseState._handleTap (package:flutter/src/material/ink_well.dart:706:14)
E/flutter (27382): #6 _InkResponseState.build.<anonymous closure> (package:flutter/src/material/ink_well.dart:789:36)
E/flutter (27382): #7 GestureRecognizer.invokeCallback (package:flutter/src/gestures/recognizer.dart:182:24)
E/flutter (27382): #8 TapGestureRecognizer.handleTapUp (package:flutter/src/gestures/tap.dart:486:11)
E/flutter (27382): #9 BaseTapGestureRecognizer._checkUp (package:flutter/src/gestures/tap.dart:264:5)
E/flutter (27382): #10 BaseTapGestureRecognizer.handlePrimaryPointer (package:flutter/src/gestures/tap.dart:199:7)
E/flutter (27382): #11 PrimaryPointerGestureRecognizer.handleEvent (package:flutter/src/gestures/recognizer.dart:467:9)
E/flutter (27382): #12 PointerRouter._dispatch (package:flutter/src/gestures/pointer_router.dart:76:12)
E/flutter (27382): #13 PointerRouter._dispatchEventToRoutes.<anonymous closure> (package:flutter/src/gestures/pointer_router.dart:117:9)
E/flutter (27382): #14 _LinkedHashMapMixin.forEach (dart:collection-patch/compact_hash.dart:379:8)
E/flutter (27382): #15 PointerRouter._dispatchEventToRoutes (package:flutter/src/gestures/pointer_router.dart:115:18)
E/flutter (27382): #16 PointerRouter.route (package:flutter/src/gestures/pointer_router.dart:101:7)
E/flutter (27382): #17 GestureBinding.handleEvent (package:flutter/src/gestures/binding.dart:218:19)
E/flutter (27382): #18 GestureBinding.dispatchEvent (package:flutter/src/gestures/binding.dart:198:22)
E/flutter (27382): #19 GestureBinding._handlePointerEvent (package:flutter/src/gestures/binding.dart:156:7)
E/flutter (27382): #20 GestureBinding._flushPointerEventQueue (package:flutter/src/gestures/binding.dart:102:7)
E/flutter (27382): #21 GestureBinding._handlePointerDataPacket (package:flutter/src/gestures/binding.dart:86:7)
E/flutter (27382): #22 _rootRunUnary (dart:async/zone.dart:1138:13)
E/flutter (27382): #23 _CustomZone.runUnary (dart:async/zone.dart:1031:19)
E/flutter (27382): #24 _CustomZone.runUnaryGuarded (dart:async/zone.dart:933:7)
E/flutter (27382): #25 _invoke1 (dart:ui/hooks.dart:273:10)
E/flutter (27382): #26 _dispatchPointerDataPacket (dart:ui/hooks.dart:182:5)
E/flutter (27382):
I/flutter (27382): Lat: 11.1115482, Long: 77.3637584
Application finished.
答案 0 :(得分：1)
您可能需要在 MyHomePage 中初始化DataBaseHelper。
helper = DataBaseHelper();