What should I do to pass events from provider to view?

[tbm98]

What should I do to pass events from provider to view? For example from the provider I want to pass an event that displays a dialog or a snackbar.

[rrousselGit]

Could you expand on this? I don't understand the question.

[tbm98]

In a real world example, when the user clicks the login button, I will call the login (username, password) function of the provider. and provider after processing will display the result of success or failure, View will display a dialog message to the user. But in this case, the provider cannot directly display the dialog message.

[rrousselGit]

It is not the role of providers to display dialogs.

Make your provider return the result, and have the UI process that result to display things

[tbm98]

I think if you do that, the view will have to handle a bit of logic. As with MVP architecture, View will only provide an interface to the presenter and the View will not implement any logic.

[rrousselGit]

Showing a modal is not business logic but UI logic.
The business logic is to set the error message.

[tbm98]

in some special cases, an intermittent process and it needs to show the message while it has not finished running. For example, the process of loading my data consists of 5 parts, and after the download is complete, each part will display a message and continue to download the next part, if processed in View, there will need 5 separate functions or At least logic view will have to call at 5 times.
like this

void loadDataClicked() async{
 final aResult = await notifier.load(a);
 if(aResult.isSuccess()){
   showDialog(aResult);
 }else{
 return;
 }

 final bResult = await notifier.load(b);
 if(bResult.isSuccess()){
   showDialog(bResult);
 }else{
 return;
 }

 final cResult = await notifier.load(c);
 if(cResult.isSuccess()){
   showDialog(cResult);
 }else{
 return;
 }

 final dResult = await notifier.load(d);
 if(dResult.isSuccess()){
   showDialog(dResult);
 }else{
 return;
 }

 final eResult = await notifier.load(e);
 if(eResult.isSuccess()){
   showDialog(eResult);
 }else{
 return;
 }
}

[tbm98]

It would be simpler to write like this:

  void showDialog(...){
    // notifier will call it or notifier send event to View => View call it
  }

  void loadDataClicked() {
    notifier.load(a,b,c,d,e);
  }

[rrousselGit]

Maybe expose a Stream and have the UI listen to it to call showDialog.

[tbm98]

but how can I listen stream (for user not use hook)?

  @override
  Widget build(BuildContext context) {
    Consumer((_, read) {
      print('state is ${read(counterProvider).state}'); //not work
    });
  .....

  @override
  Widget build(BuildContext context) {
    print('state is ${counterProvider.read(context).state}'); // can't read in build 
    ......

[rrousselGit]

stream.listen(...) or StreamBuilder

[tbm98]

Can you write a simple example about listen stream from View ?

[rrousselGit]

myProvider.read(context).myStream.listen(...)

[tbm98]

But it throw Exception when use in build.
where should I put it into if I use stateless ?

[rrousselGit]

You need a StatefulWidget for this, or hooks. You cannot listen to an object inside StatelessWidgets.

[tbm98]

You need a StatefulWidget for this, or hooks. You cannot listen to an object inside StatelessWidgets.

I think it is a best option for now.