传递version至onCreate方法并使用int类型ID查询数据库时遇'int isn't a type'错误

Let's break down the problems in your code and fix them step by step:

1. Root Cause: Method Name Conflict with Built-in Type #

The main issue throwing the "int isn't a type" error is that you named a method int()—this directly conflicts with Dart's built-in int type. When you try to use int as a type in the onCreate callback parameter, Dart gets confused and thinks you're referring to your method instead of the integer type.

Fix: Rename the method to something valid like initDatabase() or openDb().

2. Invalid whereArgs Type #

In your fetchItem method, whereArgs expects a List of values, but you're passing a Set ({id}). This will trigger a type mismatch error when you run the query.

Fix: Change {id} to [id] to use a List instead of a Set.

3. Incomplete CREATE TABLE Statement #

Your CREATE TABLE query is empty—you need to define at least one column (like the id you're using in fetchItem). Without columns, the database table creation will fail immediately.

Fix: Add columns to the table definition, e.g., id INTEGER PRIMARY KEY AUTOINCREMENT (adjust based on your actual data needs).

Corrected Code #

Here's the fully fixed version of your class with all these adjustments:

import 'dart:io';
import 'package:path/path.dart';
import 'package:sqflite/sqflite.dart';
import 'package:path_provider/path_provider.dart';

class NewsDbProvider {
  Database? db; // Mark as nullable to comply with Dart null safety

  // Renamed from int() to initDatabase() to avoid type conflict
  Future<void> initDatabase() async {
    Directory documentsDirectory = await getApplicationDocumentsDirectory();
    final path = join(documentsDirectory.path, "items.db");
    db = await openDatabase(
      path,
      version: 1,
      onCreate: (Database newDb, int version) {
        newDb.execute("""
          CREATE TABLE Items (
            id INTEGER PRIMARY KEY AUTOINCREMENT,
            -- Add your custom columns here, for example:
            title TEXT NOT NULL,
            content TEXT
          )
        """);
      },
    );
  }

  Future<List<Map<String, dynamic>>?> fetchItem(int id) async {
    if (db == null) return null; // Guard clause for uninitialized database
    return db!.query(
      "Items",
      columns: null, // Fetches all columns
      where: 'id = ?',
      whereArgs: [id], // Fixed to use a List
    );
  }
}

Additional Notes #

• I added a nullable type (Database?) for db since it's initialized asynchronously—this prevents null safety errors in Dart.
• The guard clause in fetchItem handles cases where the database hasn't been initialized yet (you should always call initDatabase() before using any database operations).

内容的提问来源于stack exchange，提问作者user8273163