Map as a function parameter in Flutter-CodePudding

Error: Non-nullable instance field id must be initialised.

Source: Picture.fromMap

import 'dart:typed_data'; // Uint8List

class Picture {
 int id;
 String title;
 Uint8List? picture;

 Picture({this.id = 0, this.title = "", this.picture });

 Picture.fromMap(Map map) {
   id = map[id];
   title = map[title];
   picture = map[picture];
 }

  Map<String, dynamic> toMap() => {
   "id": id,
   "title": title,
   "picture" : picture,
 };
}

What is the way to initialise Map when being passed to a function parameter, or how to solve this error?

CodePudding user response：

Use keyword late when you know that it will be initialized later. otherwise use int id=0; and similar for other non nullable fields as a default initialization

class Picture {
 late int id;
 late String title;
 Uint8List? picture;

 Picture({this.id = 0, this.title = "", this.picture });

 Picture.fromMap(Map map) {
   id = map[id];
   title = map[title];
   picture = map[picture];
 }

  Map<String, dynamic> toMap() => {
   "id": id,
   "title": title,
   "picture" : picture,
 };
}

CodePudding user response：

Because you init at the Picture.fromMap constructor function body. Try the below code.

import 'dart:typed_data'; // Uint8List

class Picture {
  int id;
  String title;
  Uint8List? picture;

  Picture({this.id = 0, this.title = "", this.picture});

  factory Picture.fromMap(Map map) {
    return Picture(
      id: map["id"],
      title: map["title"],
      picture: map["picture"],
    );
  }

  Map<String, dynamic> toMap() => {
        "id": id,
        "title": title,
        "picture": picture,
      };
}

import 'dart:typed_data'; // Uint8List

class Picture {
  int id;
  String title;
  Uint8List? picture;

  Picture({this.id = 0, this.title = "", this.picture});

  Picture.fromMap(Map map)
      : id = map["id"],
        title = map["title"],
        picture = map["picture"];

  Map<String, dynamic> toMap() => {
        "id": id,
        "title": title,
        "picture": picture,
      };
}

CodePudding user response：

In your code block, you didn't define variable nullable. You have to define all variables with null safety.

int? id;
String? title;
Uint8List? picture;