What is the equivalent of Android LiveData in Flutter? - flutter

Question

Android's LiveData allows to update the UI when the activity is in an active state. So if a background operation has finished while the activity is paused, the activity won't be notified and thus the app won't crush. Can Flutter perform the same behavior?

Answer 1

For people interested in an equivalent of LiveData for other scenarios, I present you StreamController:
class ExampleViewModel {
StreamController<bool> loggedInStream = StreamController<bool>();
logIn() { loggedInStream.add(true); }
}
class ExampleScreen extends StatefulWidget {
#override
State<StatefulWidget> createState() => ExampleScreenState();
}
class ExampleScreenState extends State<ExampleScreen> {
ExampleViewModel _viewModel;
BuildContext _ctx;
#override
void initState() {
super.initState();
_viewModel = ExampleViewModel()
_viewModel.loggedInStream.stream.listen( (loggedIn) {
if ( loggedIn != null && loggedIn ) {
Navigator.of(_ctx).pushReplacementNamed("/home");
}
});
}
#override
Widget build(BuildContext context) {
_ctx = context;
var loginBtn =
RaisedButton(
onPressed: _viewModel.logIn(true),
child: Text(
"LOGIN",
style: new TextStyle(
fontSize: 24.0,
)
),
color: Colors.green,
textColor: Colors.white,
);
return loginBtn;
}
#override
void dispose() {
super.dispose();
_viewModel.loggedInStream.close();
}
}
You can subscribe to it just like a LiveData, using:
loggedInStream.stream.listen( (data) { code } )
And you should clear the listeners in dispose to avoid memory leaks:
loggedInStream.close()
This code basically do the following things:
Creates a screen with a button.
Listen to a Stream (observe a LiveData).
When you click the button, it changes the value.
The listener (observer) is triggered.
Launches new screen.

Answer 2

You can use WidgetsBindingObserver to listen to the application state.
class AppLifecycleReactor extends StatefulWidget {
const AppLifecycleReactor({ Key key }) : super(key: key);
#override
_AppLifecycleReactorState createState() => new _AppLifecycleReactorState();
}
class _AppLifecycleReactorState extends State<AppLifecycleReactor> with WidgetsBindingObserver {
#override
void initState() {
super.initState();
WidgetsBinding.instance.addObserver(this);
}
#override
void dispose() {
WidgetsBinding.instance.removeObserver(this);
super.dispose();
}
AppLifecycleState _notification;
#override
void didChangeAppLifecycleState(AppLifecycleState state) {
setState(() { _notification = state; });
}
#override
Widget build(BuildContext context) {
return new Text('Last notification: $_notification');
}
}

Answer 3

Easy: Flutterx Live Data
There is no need to observe App lifecycle: widget are built only when the app is resumend
This library integrates perfectly LiveData concepts, also is well documented.
Is developed on Flutter 1.14.x-dev you need master flutter channel at the moment

Answer 4

Sorry to be late for the party,
My colleague and I have developed a library that mimics the live data of android, on flutter.
Check it out:
https://pub.dev/packages/stream_live_data