【发布时间】：2019-01-25 12:36:40
【问题描述】：
您好，我正在尝试在 Flutter 中制作应用程序，但很难找出问题所在。当您单击一个按钮时，我试图将其添加到 sqflite 数据库中，但无论我尝试什么似乎都不起作用。该值等于写入的东西，但我得到一个空错误。
这是一个将您可以选择的硬币放入列表的页面。它可以工作，但我正在尝试添加，当您单击 Listtile 时，它会将名称添加到数据库中。
import 'package:flutter/widgets.dart';
import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;
import 'dart:convert';
import 'dart:async';
import 'package:nodemarketcap/database.dart';
import 'package:sqflite/sqflite.dart';
class AddCoinPage extends StatefulWidget {
final DatabaseClient databaseClient;
AddCoinPage({Key key, @required this.databaseClient}) : super(key: key);
@override
_AddCoinPageState createState() => new _AddCoinPageState();
}
class _AddCoinPageState extends State<AddCoinPage> {
TextEditingController controller = new TextEditingController();
String coin;
addCoin(coinname) async {
setState(() {
coin = coinname;
});
return widget.databaseClient.addCoin(coin);
}
// Get json result and convert it to model. Then add
Future<Null> getUserDetails() async {
final response = await http.get(url);
final responseJson = json.decode(response.body);
setState(() {
_userDetails.clear();
for (Map user in responseJson) {
_userDetails.add(UserDetails.fromJson(user));
}
});
}
@override
void initState() {
super.initState();
getUserDetails();
}
@override
Widget build(BuildContext context) {
return new Scaffold(
appBar: new AppBar(
title: new Text('Add Coin'),
backgroundColor: new Color(0xFF090909),
elevation: 0.0,
),
body: new Column(
children: <Widget>[
new Container(
color: Colors.white,
child: new Padding(
padding: const EdgeInsets.all(8.0),
child: new Card(
child: new ListTile(
leading: new Icon(Icons.search),
title: new TextField(
controller: controller,
decoration: new InputDecoration(
hintText: 'Search', border: InputBorder.none),
onChanged: onSearchTextChanged,
),
trailing: new IconButton(icon: new Icon(Icons.cancel), onPressed: () {
controller.clear();
onSearchTextChanged('');
},),
),
),
),
),
new Expanded(
child: _searchResult.length != 0 || controller.text.isNotEmpty
? new ListView.builder(
itemCount: _searchResult.length,
itemBuilder: (context, i) {
return new Card(
child: new ListTile(
title: new Text(_searchResult[i].name),
onTap: () {addCoin((_searchResult[i].name).toString());}
),
margin: const EdgeInsets.all(0.0),
);
},
)
: new ListView.builder(
itemCount: _userDetails.length,
itemBuilder: (context, index) {
return new Card(
child: new ListTile(
title: new Text(_userDetails[index].name),
onTap: () {addCoin(_userDetails[index].name);}
),
margin: const EdgeInsets.all(0.0),
);
},
),
),
],
),
);
}
onSearchTextChanged(String text) async {
_searchResult.clear();
if (text.isEmpty) {
setState(() {});
return;
}
_userDetails.forEach((userDetail) {
if (userDetail.name.contains(text))
_searchResult.add(userDetail);
});
setState(() {});
}
}
List<UserDetails> _searchResult = [];
List<UserDetails> _userDetails = [];
final String url = 'https://nodemarketcap.com/api/api';
class UserDetails {
final String name;
UserDetails({this.name});
factory UserDetails.fromJson(Map<String, dynamic> json) {
return new UserDetails(
name: json['name'],
);
}
}
这是数据库类文件夹。我只使用其中的第一堂课；第二个是一次失败的尝试，而不是我想要的方式，但我保留了它以防我需要重复使用某些东西。
import 'dart:async';
import 'dart:io';
import 'package:path/path.dart';
import 'package:sqflite/sqflite.dart';
import 'package:path_provider/path_provider.dart';
import 'dart:convert';
class DatabaseClient {
Database database;
Future create() async {
Directory path = await getApplicationDocumentsDirectory();
String dbPath = join(path.path, "database.db");
database = await openDatabase(dbPath, version: 1,
onCreate: this._create);
}
Future _create(Database db, int version) async {
await db.execute("""
CREATE TABLE coins (
id INTEGER PRIMARY KEY,
name VARCHAR(60) NOT NULL,
nameb VARCHAR(60) NOT NULL,
tickerCap VARCHAR(60) NOT NULL,
roi DECIMAL(8, 2) NOT NULL,
usdvalue DECIMAL(20, 6) NOT NULL,
changep DECIMAL(6, 2) NOT NULL,
mnCost BIGINT UNSIGNED NOT NULL,
mncount BIGINT UNSIGNED NOT NULL,
mnpriceusd DECIMAL(20, 2) NOT NULL,
usdvol DECIMAL(30, 2) NOT NULL,
dailyUSD DECIMAL(20, 4) NOT NULL,
dailyBTC DECIMAL(20, 8) NOT NULL,
monthlyUSD DECIMAL(20, 4) NOT NULL,
monthlyBTC DECIMAL(20, 8) NOT NULL,
yearlyUSD DECIMAL(20, 4) NOT NULL,
yearlyBTC DECIMAL(20, 8) NOT NULL,
btcval DECIMAL(20, 8) NOT NULL,
usdMarketCap DECIMAL(20, 2) NOT NULL,
btcMarketCap DECIMAL(20, 2) NOT NULL,
btcvol DECIMAL(20, 8) NOT NULL
)""");
}
addCoin (String name) async {
await database.transaction((txn) async {
int id1 = await txn.rawInsert(
'INSERT INTO coins(name, nameb, tickerCap, roi, usdvalue, changep, mnCost, mncount, mnpriceusd, usdvol, dailyUSD, dailyBTC, monthlyUSD, monthlyBTC, yearlyUSD, yearlyBTC, btcval, usdMarketCap, btcMarketCap, btcvol) VALUES(name, "refresh", "refresh", 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0)');
print("insertedcoin: $id1");
});
}
updateCoin (name, nameb, tickerCap, roi, usdvalue, changep, mnCost, mncount, mnpriceusd, usdvol, dailyUSD, dailyBTC, monthlyUSD, monthlyBTC, yearlyUSD, yearlyBTC, btcval, usdMarketCap, btcMarketCap, btcvol) async {
int update = await database.rawUpdate(
'UPDATE coins SET nameb = ?, tickerCap = ?, roi = ?, usdvalue = ?, changep = ?, mnCost = ?, mncount = ?, mnpriceusd = ?, usdvol = ?, dailyUSD = ?, dailyBTC = ?, monthlyUSD = ?, monthlyBTC = ?, yearlyUSD = ?, yearlyBTC = ?, btcval = ?, usdMarketCap = ?, btcMarketCap = ?, btcvol = ? WHERE name = ?',
[nameb, tickerCap, roi, usdvalue, changep, mnCost, mncount, mnpriceusd, usdvol, dailyUSD, dailyBTC, monthlyUSD, monthlyBTC, yearlyUSD, yearlyBTC, btcval, usdMarketCap, btcMarketCap, btcvol, name]);
print("updated: $update");
}
getTest () async {
List<Map> list = await database.rawQuery('SELECT * FROM coins');
print(list);
}
}
class Coins {
Coins();
int id;
String name;
String nameb;
String tickerCap;
double roi;
double usdvalue;
double changep;
int mnCost;
int mncount;
double mnpriceusd;
double usdvol;
double dailyUSD;
double dailyBTC;
double monthlyUSD;
double monthlyBTC;
double yearlyUSD;
double yearlyBTC;
double btcval;
double usdMarketCap;
double btcMarketCap;
double btcvol;
static final columns = ["id", "name", "nameb", "tickerCap", "roi", "usdvalue", "changep", "mnCost", "mncount", "mnpriceusd", "usdvol", "dailyUSD", "dailyBTC", "monthlyUSD", "monthlyBTC", "yearlyUSD", "yearlyBTC", "btcval", "usdMarketCap", "btcMarketCap", "btcvol"];
Map toMap() {
Map map = {
"name": name,
"nameb": nameb,
"tickerCap": tickerCap,
"roi": roi,
"usdvalue": usdvalue,
"changep": changep,
"mnCost": mnCost,
"mncount": mncount,
"mnpriceusd": mnpriceusd,
"usdvol": usdvol,
"dailyUSD": dailyUSD,
"dailyBTC": dailyBTC,
"monthlyUSD": monthlyUSD,
"monthlyBTC": monthlyBTC,
"yearlyUSD": yearlyUSD,
"yearlyBTC": yearlyBTC,
"btcval": btcval,
"usdMarketCap": usdMarketCap,
"btcMarketCap": btcMarketCap,
"btcvol": btcvol
};
if (id != null) {
map["id"] = id;
}
return map;
}
static fromMap(Map map) {
Coins coins = new Coins();
coins.id = map["id"];
coins.name = map["name"];
coins.nameb = map["nameb"];
coins.tickerCap = map["tickerCap"];
coins.roi = map["roi"];
coins.usdvalue = map["usdvalue"];
coins.changep = map["changep"];
coins.mnCost = map["mnCost"];
coins.mncount = map["mncount"];
coins.mnpriceusd = map["mnpriceusd"];
coins.usdvol = map["usdvol"];
coins.dailyUSD = map["dailyUSD"];
coins.dailyBTC = map["dailyBTC"];
coins.monthlyUSD = map["monthlyUSD"];
coins.yearlyUSD = map["yearlyUSD"];
coins.yearlyBTC = map["yearlyBTC"];
coins.btcval = map["btcval"];
coins.usdMarketCap = map["usdMarketCap"];
coins.btcMarketCap = map["btcMarketCap"];
coins.btcvol = map["btcvol"];
return coins;
}
}
这是我得到的错误
08-18 15:06:20.845 19017-19136/com.nodemarketcap.nodemarketcap E/flutter: [ERROR:topaz/lib/tonic/logging/dart_error.cc(16)] Unhandled exception:
NoSuchMethodError: The method 'transaction' was called on null.
Receiver: null
Tried calling: transaction<Null>(Closure: (Transaction) => Future<Null>)
#0 Object.noSuchMethod (dart:core/runtime/libobject_patch.dart:46:5)
#1 DatabaseClient.addCoin (package:nodemarketcap/database.dart:46:20)
<asynchronous suspension>
#2 _AddCoinPageState.addCoin (package:nodemarketcap/add_coin_page.dart:26:34)
<asynchronous suspension>
#3 _AddCoinPageState.build.<anonymous closure>.<anonymous closure> (package:nodemarketcap/add_coin_page.dart:100:32)
#4 _InkResponseState._handleTap (package:flutter/src/material/ink_well.dart:494:14)
#5 _InkResponseState.build.<anonymous closure> (package:flutter/src/material/ink_well.dart:549:30)
#6 GestureRecognizer.invokeCallback (package:flutter/src/gestures/recognizer.dart:102:24)
#7 TapGestureRecognizer._checkUp (package:flutter/src/gestures/tap.dart:161:9)
#8 TapGestureRecognizer.acceptGesture (package:flutter/src/gestures/tap.dart:123:7)
#9 GestureArenaManager.sweep (package:flutter/src/gestures/arena.dart:156:27)
#10 _WidgetsFlutterBinding&BindingBase&GestureBinding.handleEvent (package:flutter/src/gestures/binding.dart:147:20)
#11 _WidgetsFlutterBinding&BindingBase&GestureBinding.dispatchEvent (package:flutter/src/gestures/binding.dart:121:22)
#12 _WidgetsFlutterBinding&BindingBase&GestureBinding._handlePointerEvent (package:flutter/src/gestures/binding.dart:101:7)
#13 _WidgetsFlutterBinding&BindingBase&GestureBinding._flushPointerEventQueue (package:flutter/src/gestures/binding.dart:64:7)
#14 _WidgetsFlutterBinding&BindingBase&GestureBinding._handlePointerDataPacket (package:flutter/src/gestures/binding.dart:48:7)
#15 _invoke1 (dart:ui/hooks.dart:134:13)
#16 _dispatchPointerDataPacket (dart:ui/hooks.dart:91:5)
所以我试图让这个工作，但我的头。我可能在做一些愚蠢的事情，所以如果有人可以告诉我我做错了什么并且可以告诉我可以改进的地方。 :P IDK，谢谢。
【问题讨论】：
-
create() 永远不会被调用 :)
-
哦，好的：我会调查一下，谢谢@diegoveloper