Flutter: How do I add data to the list?

Question

I have a code that makes a chat list from json data

      final jsonItems = (json.decode(jsonResponse.body))['messages'].cast<Map<String, dynamic>>();

      List<Messages> usersList = jsonItems.map<Messages>((json) {
        return Messages.fromJson(json);
      }).toList();

I use websockets to get a json array:

{
  "type": 13,
  "msg": {
    "id": "1",
    "ownerName": "name",
    "createdAt": "2020-06-23T21:39:46.427Z",
    "type": 1,
    "body": "Message",
  }
}

Here is my builder for displaying chat messages

FutureBuilder<List<Messages>>(
                    future: fetchJSONData(),
                    builder: (context, snapshot) {
                      if (snapshot.hasData) {
                        List<Messages> data = snapshot.data;
                        return _messagesListView(data);
                      } else if (snapshot.hasError) {
                        return Text("${snapshot.error}");
                      }

This my Map

enum MessageType {sent, received}
class Messages {
  MessageType status;
  String contactName;
  String message;
  String time;

  Messages({ this.status, this.message, this.contactName, this.time});

  factory Messages.fromJson(Map<String, dynamic> json) {
    return Messages(
        contactName: json['ownerName'],
        message: json['body'],
        time: json['createdAt'],
        status: MessageType.received
    );
  }
}

I have already done getting data from websockets, but how can I add a new message to the list that I received from websockets, and that the message would appear on the screen

Omer Gamliel · Accepted Answer · 2020-06-23 22:16:23Z

1

You need to use ConnectionState inside your builder. Look at this code template: (Currently your builder return Text Widget without waiting for the future to complete)

return FutureBuilder<List<Messages>>(
     future: fetchJSONData(),
    builder: (context, snapshot) {
      if (snapshot.connectionState == ConnectionState.done) {
        // future complete
        // if error or data is false return error widget
        if (snapshot.hasError || !snapshot.hasData) {
          return Text("${snapshot.error}");
        }

        // return data widget
         List<Messages> data = snapshot.data;
         return _messagesListView(data);

        // return loading widget while connection state is active
      } else
        return Center(
        child: CircularProgressIndicator());
             
    },
  );

edited Jun 23, 2020 at 22:16

answered Jun 23, 2020 at 22:04

Omer Gamliel

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6 Comments

ike13 Over a year ago

Until I do something on the screen, the message doesn't appear

Omer Gamliel Over a year ago

what do you mean by do something on the screen?

ike13 Over a year ago

Let's say that until I click anywhere in the app, the message doesn't appear

ike13 Over a year ago

Same. Maybe need use StreamBuilder? I'm beginner in flutter

Omer Gamliel Over a year ago

StreamBuilder used for changes in the displayed data. In your case, FutureBuilder is fine. Did you copy my code snippet and the Text widget is not showing?

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