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タイプ「Future <dynamic>」は、フラッターデータベース作成のタイプ「Future <int>」例外のサブタイプではありません

私はフラッターアプリケーション開発に不慣れです。 Flutterアプリケーションでは、パスプロバイダープラグインとSQFLiteを使用してデータベースを作成します。しかし、それは機能していません。例外メッセージタイプ「Future」がタイプ「Future」のサブタイプではないことを示しています。

ここにコードを追加します

 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;
  }

私を助けてください。提案をお願いします。前もって感謝します。

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

これは私が取得したログです。

dartflutterflutter-dependencies
3
Rosemary

onCreate()関数は（voidではなく）Future型であり、asyncである必要があります。

1
Roya