Flutter Errror with example database code: The argument type 'dynamic' can't be assig-CodePudding

In the flutter database example code: https://docs.flutter.dev/cookbook/persistence/sqlite

This block of code throws 3 errors:

 // Convert the List<Map<String, dynamic> into a List<Dog>.
return List.generate(maps.length, (i) {
  return Dog(
    id: maps[i]['id'],
    name: maps[i]['name'],
    age: maps[i]['age'],
  );
});

}

The errors are:

The argument type 'dynamic' can't be assigned to the parameter type 'int'.
The argument type 'dynamic' can't be assigned to the parameter type 'String'.
The argument type 'dynamic' can't be assigned to the parameter type 'int'.

and vscode highlights the "maps" section of the line (maps[i])

I dont know what version of flutter the guide was targeting, but my guess is that it's a problem maybe in newer flutter versions? I'm trying to learn flutter and how to use sqlite, so this has me stuck. Thanks in advance for any input!

For reference, here's the whole code block:

import 'dart:async';

import 'package:flutter/widgets.dart';
import 'package:path/path.dart';
import 'package:sqflite/sqflite.dart';

void main() async {
  // Avoid errors caused by flutter upgrade.
  // Importing 'package:flutter/widgets.dart' is required.
  WidgetsFlutterBinding.ensureInitialized();
  // Open the database and store the reference.
  final database = openDatabase(
    // Set the path to the database. Note: Using the `join` function from the
    // `path` package is best practice to ensure the path is correctly
    // constructed for each platform.
    join(await getDatabasesPath(), 'doggie_database.db'),
    // When the database is first created, create a table to store dogs.
    onCreate: (db, version) {
      // Run the CREATE TABLE statement on the database.
      return db.execute(
        'CREATE TABLE dogs(id INTEGER PRIMARY KEY, name TEXT, age INTEGER)',
      );
    },
    // Set the version. This executes the onCreate function and provides a
    // path to perform database upgrades and downgrades.
    version: 1,
  );

  // Define a function that inserts dogs into the database
  Future<void> insertDog(Dog dog) async {
    // Get a reference to the database.
    final db = await database;

    // Insert the Dog into the correct table. You might also specify the
    // `conflictAlgorithm` to use in case the same dog is inserted twice.
    //
    // In this case, replace any previous data.
    await db.insert(
      'dogs',
      dog.toMap(),
      conflictAlgorithm: ConflictAlgorithm.replace,
    );
  }

  // A method that retrieves all the dogs from the dogs table.
  Future<List<Dog>> dogs() async {
    // Get a reference to the database.
    final db = await database;

    // Query the table for all The Dogs.
    final List<Map<String, dynamic>> maps = await db.query('dogs');

    // Convert the List<Map<String, dynamic> into a List<Dog>.
    return List.generate(maps.length, (i) {
      return Dog(
        id: maps[i]['id'],
        name: maps[i]['name'],
        age: maps[i]['age'],
      );
    });
  }

  Future<void> updateDog(Dog dog) async {
    // Get a reference to the database.
    final db = await database;

    // Update the given Dog.
    await db.update(
      'dogs',
      dog.toMap(),
      // Ensure that the Dog has a matching id.
      where: 'id = ?',
      // Pass the Dog's id as a whereArg to prevent SQL injection.
      whereArgs: [dog.id],
    );
  }

  Future<void> deleteDog(int id) async {
    // Get a reference to the database.
    final db = await database;

    // Remove the Dog from the database.
    await db.delete(
      'dogs',
      // Use a `where` clause to delete a specific dog.
      where: 'id = ?',
      // Pass the Dog's id as a whereArg to prevent SQL injection.
      whereArgs: [id],
    );
  }

  // Create a Dog and add it to the dogs table
  var fido = const Dog(
    id: 0,
    name: 'Fido',
    age: 35,
  );

  await insertDog(fido);

  // Now, use the method above to retrieve all the dogs.
  print(await dogs()); // Prints a list that include Fido.

  // Update Fido's age and save it to the database.
  fido = Dog(
    id: fido.id,
    name: fido.name,
    age: fido.age   7,
  );
  await updateDog(fido);

  // Print the updated results.
  print(await dogs()); // Prints Fido with age 42.

  // Delete Fido from the database.
  await deleteDog(fido.id);

  // Print the list of dogs (empty).
  print(await dogs());
}

class Dog {
  const Dog({
    required this.id,
    required this.name,
    required this.age,
  });
  final int id;
  final String name;
  final int age;

  // Convert a Dog into a Map. The keys must correspond to the names of the
  // columns in the database.
  Map<String, dynamic> toMap() {
    return {
      'id': id,
      'name': name,
      'age': age,
    };
  }

  // Implement toString to make it easier to see information about
  // each dog when using the print statement.
  @override
  String toString() {
    return 'Dog{id: $id, name: $name, age: $age}';
  }
}

CodePudding user response：

Try doing this -

return List.generate(maps.length, (i) {
      return Dog(
        id: maps[i]['id'] as int,
        name: maps[i]['name'] as String,
        age: maps[i]['age'] as int,
      );
    });
    }

CodePudding user response：

Create below method in your Dog model

Dog.fromJson(Map<String, dynamic> json)
          : id = json['id'],
            name = json['name'],
            age = json['age'];

For usage:

return List.generate(maps.length, (i) {
      return Dog.fromJson(maps[i]);
    });
    }

I'd faced same error but this solution works for me, hope it works for you too