NullReference fix in ShellPageRendererTracker.UpdateTabBarVisibility()

[Marioo1357]

Description of Change

Check if Page and ViewController are not null in ShellPageRendererTracker.UpdateTabBarVisibility()

Issues Fixed

Fixes #26784

[dotnet-policy-service]

Hey there @Marioo1357! Thank you so much for your PR! Someone from the team will get assigned to your PR shortly and we'll get it reviewed.

[PureWeen]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 3 pipeline(s).

[mattleibow]

@PureWeen is this small change just hiding some sinister bug somewhere or is it expected that VC and Page may be null at this point? I see a few null checks in places, so I am not super afraid, but it is bugging me a bit.

Regardless, this change will stop a crash, but the possible nulls are causing me to think things.

[PureWeen]

It looks like the VC is GC-ing while this is still attached.
I'm curious why that's happening

I think that's not reason to block this PR as this PR should help somewhat.

Though I think this might just push the exception down to UpdateLeftToolbarItems which also references the VC.

It'd be good to have a followup PR where we check for VC going null in a couple more places.

[Marioo1357]

@mattleibow @PureWeen
We also catched one in other place in Shell. I Wonder why whole project is not nullabe friendly?
Isn't better to just remove #disable nullable and fix warrings by a null checks?

[PureWeen]

@mattleibow @PureWeen We also catched one in other place in Shell. I Wonder why whole project is not nullabe friendly? Isn't better to just remove #disable nullable and fix warrings by a null checks?

Ultimately yes, but just haven't scheduled this effort yet

We'll look at doing a sweep through on NET10

we can't change any of the nullability on public APIs during a service release so we fix these in waves as we have time during major releases.

I did what I could for now here
#27160

which should help

We also catched one in other place in Shell.

Can you create an issue?