我有一个使用 sqflite 数据库的颤振应用程序。它可以在 android 模拟器和设备上完美运行，也可以在 ios 模拟器上运行。在 ios 真实设备上它可以工作，但不能保存或检索数据，只是静态空 UI 我使用 xcode 10.1，在 iphone 6 上使用 ios 11.2.6，在 iphone 5s 上使用 ios 12.1.4。
import 'package:sqflite/sqflite.dart';
import 'dart:async';
import 'dart:io';
import 'package:path_provider/path_provider.dart';
import 'package:flutter_app/models/note.dart';
class DatabaseHelper {
static DatabaseHelper _databaseHelper; // Singleton DatabaseHelper
static Database _database; // Singleton Database
String noteTable = 'note_table';
String colId = 'id';
String colTitle = 'title';
String colDescription = 'description';
String colPriority = 'priority';
String colDate = 'date';
DatabaseHelper._createInstance(); // Named constructor to create instance of DatabaseHelper
factory DatabaseHelper() {
if (_databaseHelper == null) {
_databaseHelper = DatabaseHelper._createInstance(); // This is executed only once, singleton object
}
return _databaseHelper;
}
Future<Database> get database async {
if (_database == null) {
_database = await initializeDatabase();
}
return _database;
}
Future<Database> initializeDatabase() async {
// Get the directory path for both Android and iOS to store database.
Directory directory = await getApplicationDocumentsDirectory();
String path = directory.path + 'notes.db';
// Open/create the database at a given path
var notesDatabase = await openDatabase(path, version: 1, onCreate: _createDb);
return notesDatabase;
}
void _createDb(Database db, int newVersion) async {
await db.execute('CREATE TABLE $noteTable($colId INTEGER PRIMARY KEY AUTOINCREMENT, $colTitle TEXT, '
'$colDescription TEXT, $colPriority INTEGER, $colDate TEXT)');
}
// Fetch Operation: Get all note objects from database
Future<List<Map<String, dynamic>>> getNoteMapList() async {
Database db = await this.database;
// var result = await db.rawQuery('SELECT * FROM $noteTable order by $colPriority ASC');
var result = await db.query(noteTable, orderBy: '$colPriority ASC');
return result;
}
// Insert Operation: Insert a Note object to database
Future<int> insertNote(Note note) async {
Database db = await this.database;
var result = await db.insert(noteTable, note.toMap());
return result;
}
// Update Operation: Update a Note object and save it to database
Future<int> updateNote(Note note) async {
var db = await this.database;
var result = await db.update(noteTable, note.toMap(), where: '$colId = ?', whereArgs: [note.id]);
return result;
}
// Delete Operation: Delete a Note object from database
Future<int> deleteNote(int id) async {
var db = await this.database;
int result = await db.rawDelete('DELETE FROM $noteTable WHERE $colId = $id');
return result;
}
// Get number of Note objects in database
Future<int> getCount() async {
Database db = await this.database;
List<Map<String, dynamic>> x = await db.rawQuery('SELECT COUNT (*) from $noteTable');
int result = Sqflite.firstIntValue(x);
return result;
}
// Get the 'Map List' [ List<Map> ] and convert it to 'Note List' [ List<Note> ]
Future<List<Note>> getNoteList() async {
var noteMapList = await getNoteMapList(); // Get 'Map List' from database
int count = noteMapList.length; // Count the number of map entries in db table
List<Note> noteList = List<Note>();
// For loop to create a 'Note List' from a 'Map List'
for (int i = 0; i < count; i++) {
noteList.add(Note.fromMapObject(noteMapList[i]));
}
return noteList;
}
}
此代码是 youtube 上的教程，仅适用于 android 和 ios 模拟器