Allow accessing state (readonly) during lifecycle callbacks

[holzgeist]

Is your feature request related to a problem? Please describe.
Related to #4352. Use case: cleanup timers etc stored in state during onDispose

Describe the solution you'd like
I'd like a readonly view of state during lifecycle callbacks. Especially onDispose, but I guess onCancel and onResume would be interesting too for others.

I can think of two ways to implement this:

• allow readonly access to state during those callbacks (but prevent writes)
• pass current state as part of onDispose callback

Describe alternatives you've considered
The examples usually use final variables in build and access them during cleanup. In my scenario, the value can change over time, so this approach doesn't work.
All other ideas that I came up with are hacky at best and I didn't even verify if they would work (static variables, member variables that duplicate the relevant values of state etc)

Additional context
N/A

[rrousselGit]

The main issue is that we'd have to change the behavior specifically for those lifecycles.

Currently, reading state will rebuild the provider if need be.

[holzgeist]

Ok, in that case, my second idea would be better. Adding the last know state to lifecycle callbacks would only touch the correct code areas without meddling with state getter. It would also make clearer that one cannot update state, just read whatever is passed as parameter.

However, adding a parameter to a callback (even an optional one) is a breaking change. And you just did 3.0.
And adding onDisposeWithState etc. doesn't really make sense either IMHO

[rrousselGit]

Don't worry about versioning. I don't mind making breaking changes if that's warranted. And there are ways to introduce this change more softly.

There could be ways to do this. But for now, I'm not sure how much traction this would get. I think I'll leave this open for some time and see if it picks up 👍

[holzgeist]

Ok, let's see if the 👍 counter increases on the issue description

Meanwhile I have an idea to work around this (not verified yet):

• not only store the timer in state, but also the cancel function returned by onDispose.
• add a timer cancellation onDispose every time I update the timer