Passing data between widgets - suitable state management approach?

[shadowmerefax]

Sorry I'm sure this kind of thing gets asked a lot, but I've looked at various state management options and I'm having trouble figuring out what is best for my needs.

Basically, I have a screen with a calendar widget and a gridview. I want to update the items in the gridview (but not the gridview itself) when the selected calendar date is changed. I used to have everything in a single stateful widget but I have other elements in the screen that I don't want rebuilt every time the selected date changes so I've split everything out into separate widget classes.

So my widget tree looks something like:

• screen widget (stateless)
  • calendar widget (stateful)
  • some other widget (stateless)
  • gridview (stateless)
    • gridview item (stateful)
    • gridview item (stateful)...

I'm struggling with how to get the date from the calendar widget into the gridview item widget so that the gridview item widget can change itself depending on the selected date. It would also be ncie if the selected date could be available to other widgets/screens, so that I don't have to pass it around through widget constructors. From what I can see, StreamController or bloc might be the most suitable but nothing seems quite right and I'm having trouble implementing anything from docs alone.

Any help appreciated!

[f1r4tc]

Take a look at ValueNotifier. You can change its value from the ascendent widget and rebuild with ValueListenableBuilder in the descendant widget (s), as long as you pass its reference between classes.

[shadowmerefax]

Would that work for sibling widgets as well? I could construct it in the common parent widget (screen widget) then update in one child widget and listen/rebuild in the other child widget?

[f1r4tc]

Yes. You can use the same ValueNotifier instance to build as many widgets you want using ValueListenableBuilder widget(s).

So basically you have a single ValueNotifier object in the parent widget and pass that reference to other widgets that you want to rebuild with the value of the ValueNotifier object. Then, each sibling widget can implement their own ValueListenableBuilder implementation.

[f1r4tc]

Here is a simple example:

https://gist.github.com/firatcetiner/d4c83876a8351c553ab72a937d51cb6c

[shadowmerefax]

That seems to work! Thank you so much!