qt: introduce `FocusReasonForwarder`

This is useful for getting rid of setCurrentItemFocus() for good. If delegate or a leaf item does not get the focus reason, we can manually forward using this. Currently, Qt does not expose the last focus reason in QQuickItem, unlike QQuickControl.

Request review @chub.

added MRStatus::Reviewable label

changed milestone to %4.0

added Component::Interface: Qt label

requested review from @chub

added MRStatus::WaitingForReviewerFeedback label and removed MRStatus::Reviewable label

Could you apply this in a place or two in our codebase (I don't ask you convert the whole project) so we can see places where this could replace setCurrentItemFocus?

My understanding is that this could help reduce cases where we have some Navigation.leftAction: myItem.setCurrentItemFocus(reason), I guess we still need some manual code for page switching

Do you know if Qt 6.2 already fixed this problem? If I remember correctly, the problem in Qt 5 was that:

ListView {
  // This is a focus scope
  delegate: Control {
    focus: (index === 0)
  }  
}

When we forceActiveFocus(TabReason) the focus scope (which is Navigation.item or KeyNavigation.item behavior), Control delegate instance that requests focus (focus: true) did not have its focusReason adjusted even though it gets the active focus.

hum, you can't put raw controls directly in a list, you're supposed to use ItemDelegate or this causes focus & navigation issues (but that may be a misuse in your sample).

When I tested the HomePage MR, I tried to remove the KeyNavigation.action and it was working fine for lists, getting initial focus was not working properly with GridView but I assume that's an implementation issue that could be fixed on our side (grid item was getting focus but didn't get the focusReason).

to be taken with a grain of salt, I only briefly checked this

hum, you can't put raw controls directly in a list, you're supposed to use ItemDelegate or this causes focus & navigation issues (but that may be a misuse in your sample).

I don't know what makes ItemDelegate different from Control in this regard. If ItemDelegate fixes this issue, then we can use it instead in delegate and not proceed with this merge request, but then I would ask why setCurrentItemFocus() was brought then.

that's an implementation issue that could be fixed on our side (grid item was getting focus but didn't get the focusReason)

My idea was to use this like this to get the focus reason of the view:

GridDelegate {
  // This derives from Control
  Binding on focusReason {
    value: view.FocusReasonForwarder.focusReason
  }
}

This means we get rid of setCurrentItemFocus(), but rather simply focus the view. This is a focus scope, the delegate instance that had the focus last time would retain its focus even when it loses its active focus. When the view gets the active focus, the same item would also get the active focus. So we should not need to set focus to true or call forceActiveFocus() in the delegate instance.

My idea was to use this like this to get the focus reason of the view

One problem with this approach is that, the delegate may have different focus reason from the view (navigating within the view?). So maybe an all-time binding is not a good idea. Or maybe focus reason must be the same in all active focus items (ancestors)?

added MRStatus::InReview label and removed MRStatus::WaitingForReviewerFeedback label