Flutter: type 'List<dynamic>' is not a subtype of type 'Map<String, dynamic>' in type cast

Question

Im trying to make a list ti json for firestore, and have the following code:

  static Map<String, dynamic> toJson(Message? message) => {
        'id': message?.id,
        'senderId': message?.senderId,
        'receiverId': message?.receiverId,
        'message': message?.message,
        'dateTime': message?.dateTime,
        'timeString': message?.timeString,
        'likes': message?.likes,
        'chatId': message?.chatId,
        'commentCount': message?.commentCount,
        'userIdsWhoLiked': message?.userIdsWhoLiked,
      };

  static Map<String, dynamic> messageListToJson(List<Message?> messages) {
    Map<String, dynamic> messageList = [] as Map<String, dynamic>;
    for (Message? message in messages) {
      messageList.addAll(Message.toJson(message));
    }
    return messageList;
  }

The error is "type 'List' is not a subtype of type 'Map<String, dynamic>' in type cast". For some reason, this is the part throwing the error:

Map<String, dynamic> messageList = [] as Map<String, dynamic>;

Its weird because i have a similar piece of code that works despite being nearly identical. Any idea whats causing this?

To avoid such problems, you can generate models from YAML descriptions. And you will have built-in methods List<Model> Model.fromJsonList(List json), List<Map<String, dynamic>> Model.toJsonList(List<Model> list). stackoverflow.com/a/73091698/1737201 stackoverflow.com/a/66464998/1737201 — mezoni
– mezoni, Commented Jul 24, 2022 at 14:42

Kaushik Chandru · Accepted Answer · 2022-07-23 04:47:06Z

1

You are trying to assign a list to a map

Map<String, dynamic> messageList = []

Here [] is an empty list.

You can try this

List<Map<String, dynamic>> messageList = [];

You can try this

Map<String, dynamic> messageList;

edited Jul 23, 2022 at 4:47

answered Jul 23, 2022 at 4:13

Kaushik Chandru

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1 Comment

Ruder Buster Over a year ago

Id like this output to be a single Map of multiple entries if possible, rather than a list of Maps.

Abubakar shaikh · Accepted Answer · 2022-07-23 08:01:01Z

1

[] can't be used as Map. Because it is List.

Map<String, dynamic> messageList = [] as Map<String, dynamic>;

Use this {}.

Map<String, dynamic> messageList = {} as Map<String, dynamic>;

I hope it could help.

answered Jul 23, 2022 at 8:01

Abubakar shaikh

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1 Comment

Randal Schwartz Over a year ago

{} as Map<String, dynamic> is better written as Map<String,dynamic>{}

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