I have a Provider model such as provider_model.dart:

import 'package:flutter/material.dart';

class ProviderModel extends ChangeNotifier {
  final List<String> _myList = [];

  List<String> get myList => [..._myList];

  void addItem(String item) {
    _myList.add(item);
    notifyListeners();
  }
}

Now, Flutter documentation Now, when I click on the send button, it calls _sendMessage() (code above). And then since the StreamBuilder() hasData it runs this line (code above):

provider.addItem('I was added');

However, this is where my error appears, I am getting the following error:

The following assertion was thrown while dispatching notifications for ProviderModel:
setState() or markNeedsBuild() called during build.

• Why am I getting this error? Where is the widget rebuilding? See this answer to Flutter Provider setState() or markNeedsBuild() called during build

CodePudding user response：

You can take help from addPostFrameCallback, but the cost is it will keep rebuilding on every frame, to control this behavior you can use a bool on state class.

  bool isDone = false;

  void addItemH() {
    if (!isDone) {
      WidgetsBinding.instance.addPostFrameCallback((timeStamp) {
        Provider.of<ProviderModel>(context, listen: false)
            .addItem('I was added');
        isDone = true;
      });
    }
  }

And builder

 builder: (context, snapshot) {
                if (snapshot.hasData) {
                  addItemH();
                  return Text("Item added");

And to control the next insertaion.

  void _sendMessage() {
    if (_controller.text.isNotEmpty) {
      isDone = false;
      _channel.sink.add(_controller.text);
      print('done');
    }
  }
}

If you just want to add data only single time, it is better to do inside inside initState.