How to give a default value to a textfield when using bloc framework

You can give your behaviorSubject a seed value that will be used as its initial value by doing this.

final nameStreamController = BehaviorSubject<String>.seeded('InitialName');  

for older versions of rxDart, use

final nameStreamController = BehaviorSubject<String>(seedValue:'InitialName'); 

Without knowing what you want to do with the name field, there are a few routes you can go.

You could supply a hintText to the InputDecoration (InputDecoration(hintText: 'name')).

You could set an initial value on the StreamBuilder:

StreamBuilder(  stream: bloc.nameStream,  initialData: 'Initial Name',    builder: (context, snapshot) {      return TextField(        onChanged: bloc.nameChangedStream,        decoration: InputDecoration(labelText: 'Enter name' ),      );    }  ),

Though, that won't persist that value in the stream, so if the user doesn't change the text field, 'Initial Name' won't be in your nameStreamController's stream.

As @nonybrighto mentioned, you can seed your nameStreamController with the initial value.

If you cannot use a seeded value, you could also add an initial value to your stream during the bloc's init:

class Bloc {  final nameStreamController = BehaviorSubject<String>();  Stream<String> get nameStream => nameStreamController.stream;  Function(String) get nameChangedStream => nameStreamController.sink.add;  Bloc() {    String initialValue = _getInitialValue();    nameStreamController.add(initialValue);  }}

Here's a more full, real-world example: we found this authentication and login BLoC example in which we followed a lot of the stuff laid out here: Didier Boelens BloC Example. It shows you how can use BLoC, reactive programming, and streams to set up a registration form and auth.