Using `notifyListeners()` inside `onDateChange` not working

[psygo]

Describe the bug

Whenever the user changes the calendar date, something should happen in my program. At least a class I created to store my screen's data should change. In order to do so, I'm calling a method that changes the internal data and then calling notifyListeners() to update other fields. However, if I use notifyListeners(), the selected date on the calendar doesn't change; the data does change, but not the selected rectangle on the screen.

To Reproduce

The code in my app is quite long, but I believe the following should suffice...

The DatePickerTimeline call:

DatePickerTimeline(
  DateTime.now(),
  onDateChange: (newDate){
    data.changeDay(date: newDate);
  }

The method to update the data is something like:

void changeDay({DateTime date}){
  this.day = date;
  notifyListeners();
}

Expected behavior

Why is the selected rectangle not being selected? I've also tried to refactor the code to use the Provider package instead of setState() but it didn't work either.

Desktop (please complete the following information):

• OS: Windows 10
• Browser: Firefox

Smartphone (please complete the following information):

• Device: Nexus 6
• OS: Android 9.0

[psygo]

I'm leaning more and more on blaming the interaction of setState and notifyListeners. After wrapping the Container from the DatePickerTimeline widget source code and replacing widget.currentDate by a Consumer<> with data.currentDate (and adding notifyListeners), everything seems to work fine.

[iamvivekkaushik]

I am not sure why this is happening. onDateChange is called after data has been changed which should change the background to respective date.

[iamvivekkaushik]

This seems to be working fine make sure you are implementing it correctly.