类型 'Future<dynamic>' 不是 Flutter 数据库创建中的“Future<int>”类型异常的子类型
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【中文标题】类型 \'Future<dynamic>\' 不是 Flutter 数据库创建中的“Future<int>”类型异常的子类型【英文标题】:type 'Future<dynamic>' is not a subtype of type 'Future<int>' exception in flutter database creation类型 'Future<dynamic>' 不是 Flutter 数据库创建中的“Future<int>”类型异常的子类型 【发布时间】:2018-12-31 15:17:42 【问题描述】:我是 Flutter 应用程序开发的新手。在我的颤振应用程序中,我使用路径提供程序插件和 SQFLite 创建了一个数据库。但它不起作用,它显示一条异常消息 “未来”类型不是“未来”类型的子类型
我在这里添加我的代码
static final DatabaseHelper _instance = new DatabaseHelper.internal();
factory DatabaseHelper() => _instance;
static Database _db;
Future<Database> get db async
if (_db != null)
return _db;
_db = await initDb();
return _db;
DatabaseHelper.internal();
initDb() async
Directory documentDirectory = await getApplicationDocumentsDirectory();
String path = join(documentDirectory.path, "tododatabase.db");
var ourDb = await openDatabase(path, version: 1, onCreate: _onCreate);
return ourDb;
Future _onCreate(Database db, int version) async
await db.execute(
"CREATE TABLE TodoList(id INTEGER PRIMARY KEY, todoText TEXT)");
// print("Table is created");
//insertion
Future<int> saveTodo(Todo todo) async
var dbClient = await db;
int res = await dbClient.insert(" TodoList", todo.toMap());
return res;
请帮助我。请给个建议。提前致谢。
0631/com.stunntech.fluttertodoapp E/flutter: [ERROR:topaz/lib/tonic/logging/dart_error.cc(16)] Unhandled exception:
type '(Database, int) => void' is not a subtype of type '(Database, int) => Future<dynamic>'
#0 DatabaseHelper.initDb (package:flutter_todo_app/database/database.dart:29:64)
<asynchronous suspension>
#1 DatabaseHelper.db (package:flutter_todo_app/database/database.dart:20:17)
<asynchronous suspension>
#2 DatabaseHelper.saveTodo (package:flutter_todo_app/database/database.dart:40:26)
<asynchronous suspension>
#3 _MyTodoListState._submitTodo (package:flutter_todo_app/todo_list.dart:144:30)
<asynchronous suspension>
#4 _MyTodoListState._showAlert.<anonymous closure> (package:flutter_todo_app/todo_list.dart:97:19)
#5 GestureRecognizer.invokeCallback (package:flutter/src/gestures/recognizer.dart:102:24)
#6 TapGestureRecognizer._checkUp (package:flutter/src/gestures/tap.dart:161:9)
#7 TapGestureRecognizer.handlePrimaryPointer (package:flutter/src/gestures/tap.dart:94:7)
#8 PrimaryPointerGestureRecognizer.handleEvent (package:flutter/src/gestures/recognizer.dart:315:9)
#9 PointerRouter._dispatch (package:flutter/src/gestures/pointer_router.dart:73:12)
#10 PointerRouter.route (package:flutter/src/gestures/pointer_router.dart:101:11)
#11 _WidgetsFlutterBinding&BindingBase&GestureBinding.handleEvent (package:flutter/src/gestures/binding.dart:143:19)
#12 _WidgetsFlutterBinding&BindingBase&GestureBinding.dispatchEvent (package:flutter/src/gestures/binding.dart:121:22)
#13 _WidgetsFlutterBinding&BindingBase&GestureBinding._handlePointerEvent (package:flutter/src/gestures/binding.dart:101:7)
#14 _WidgetsFlutterBinding&BindingBase&GestureBinding._flushPointerEventQueue (package:flutter/src/gestures/binding.dart:64:7)
#15 _WidgetsFlutterBinding&BindingBase&GestureBinding._handlePointerDataPacket (package:flutter/src/gestures/binding.dart:48:7)
#16 _invoke1 (dart:ui/hooks.dart:134:13)
#17 _dispatchPointerDataPacket (dart:ui/hooks.dart:91:5)enter code here
这是我得到的日志。
【问题讨论】:
哪一行导致错误? var ourDb = await openDatabase(path, version: 1, onCreate: _onCreate);openDatabase()
来自哪里?
它来自数据库类
问题可能出在那儿。
【参考方案1】:
您的onCreate()
函数应该是void
类型(而不是Future
)并且应该是async
!
【讨论】:
【参考方案2】:您需要有一个 Future 为您的 initDB() 方法返回类型数据库:
Future<Database> initDB() async
var databasesPath = await getDatabasesPath();
String path = join(databasesPath, "event.db");
var theDatabase = await openDatabase(path, version: 1, onCreate: _onCreate);
return theDatabase;
这里有一个完整的例子:
https://github.com/dazza5000/austin-feeds-me-flutter/blob/master/lib/data/event_database.dart
class EventsDatabase
static const EVENT_TABLE_NAME = "event";
static final EventsDatabase _instance = EventsDatabase._internal();
factory EventsDatabase() => _instance;
static Database _db;
Future<Database> get db async
if (_db != null)
return _db;
_db = await initDB();
return _db;
EventsDatabase._internal();
Future<Database> initDB() async
var databasesPath = await getDatabasesPath();
String path = join(databasesPath, "event.db");
var theDatabase = await openDatabase(path, version: 1, onCreate: _onCreate);
return theDatabase;
void _onCreate(Database db, int version) async
await db.execute("CREATE TABLE " + EVENT_TABLE_NAME + " ("
"id STRING PRIMARY KEY, "
"name TEXT, "
"time INTEGER, "
"description TEXT, "
"url TEXT, "
"photo TEXT, "
"lat DOUBLE, "
"lng DOUBLE)");
Future closeDb() async
var dbClient = await db;
return dbClient.close();
【讨论】:
如您所说更改了我的代码。但同样的错误再次出现。 请发布日志、确切的异常和行号。您的问题可能在插入语句中。 我添加了我在问题中得到的日志。你能检查一下吗? 如果您更改了代码,请将更新后的代码也放入。谢谢。 能否更新 onCreate 以返回 void "void _onCreate(Database db, int version) async"以上是关于类型 'Future<dynamic>' 不是 Flutter 数据库创建中的“Future<int>”类型异常的子类型的主要内容,如果未能解决你的问题,请参考以下文章
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