flutter 2.0 : How to create a model class for firestore snapshot

Question

如何为flutter 2.0的firestore快照构建flutter类
我试过这样的事情:

import 'package:cloud_firestore/cloud_firestore.dart';

class Post {
  final String pid;
  final String description;

  final DocumentReference reference;

  Post.fromMap(Map<String, dynamic> map, this.pid, this.description, {required this.reference})

  Post.fromSnapshot(DocumentSnapshot snapshot)
      : this.fromMap(snapshot.data(), reference: snapshot.reference);

  @override
  String toString() => "Post<$pid:$description>";
}

但是有一个错误说需要 3 个位置参数，但找到了 1 个。
任何帮助将不胜感激。

Answer 1

你没有通过 pid和 description (这是位置参数)。您可以使它们成为可选的命名参数或显式传递它们。
解决方案1(使参数可选):

class Post {
  final String pid;
  final String description;
  final DocumentReference reference;

  Post.fromSnapshot(DocumentSnapshot snapshot)
      : this.fromMap(
          snapshot.data() as Map<String, dynamic>,
          reference: snapshot.reference,
        );

  Post.fromMap(
    Map<String, dynamic> map, {
    required this.reference,
    this.pid = 'dummyID',
    this.description = 'dummyDesc',
  });

  @override
  String toString() => 'Post<$pid:$description>';
}

方案二(传参数):

class Post {
  final String pid;
  final String description;
  final DocumentReference reference;

  Post.fromSnapshot(DocumentSnapshot snapshot)
      : this.fromMap(
          snapshot.data() as Map<String, dynamic>,
          'pid',
          'description',
          reference: snapshot.reference,
        );

  Post.fromMap(
    Map<String, dynamic> map,
    this.pid,
    this.description, {
    required this.reference,
  });

  @override
  String toString() => 'Post<$pid:$description>';
}