Summary:
VirtualizedList_EXPERIMENTAL has a different flow signature from VirtualizedList. This does not cause an error in unit tests, which are untyped, but prevents injecting VirtualizedList_EXPERIMENTAL via the current API from flowtype. This diff updates the injection interface to allow a more relaxed type, validating safety at runtime.
Changelog:
[Internal][Changed] - Allow injecting looser VirtualizedList
Reviewed By: javache
Differential Revision: D38143682
fbshipit-source-id: 054bbc5092823f4e4413d69d3d72a7ecdd71a6a2
Summary:
# This Change
https://github.com/react-native-community/discussions-and-proposals/pull/335 discussed a set of problems with VirtualizedList and focus. These were seen as severe externally for a11y on desktop. The issues center on users of keyboard and accessibility tools, where users expect to be able to move focus in an uninterrupted loop.
The design and implementation evolved to be a bit more general, and without any API-surface behavior changes. It was implemented and rolled out externally as a series of changes. The remaining changes that were not upstreamed into RN are rolled into https://github.com/facebook/react-native/pull/32646
This diff brings this change into the repo, as a separate copy of VirtualizedList, to measure its impact to guardrail metrics, without yet making it the default implementation. The intention is for this to be temporary, until there is confidence the implementation is correct.
## List Implementation (more on GitHub)
This change makes it possible to synchronously move native focus to arbitrary items in a VirtualizedList. This is implemented by switching component state to a sparse bitset. This was previously implemented and upstreamed as `CellRenderMask`.
A usage of this is added, to keep the last focused item rendered. This allows the focus loop to remain unbroken, when scrolling away, or tab loops which leave/re-enter the list.
VirtualizedList tracks the last focused cell through the capture phase of `onFocus`. It will keep the cell, and a viewport above and below the last focused cell rendered, to allow movement to it without blanking (without using too much memory).
## Experimentation Implementation
A mechanism is added to gate the change via VirtualizedListInjection, mirroring the approach taken for Switch with D27381306 (https://github.com/facebook/react-native/commit/683b825b327e7fa71e87e3d613cb9acd37c24288).
It allows VirtualizedList to delegate to a global override. It has a slight penalty to needing to import both modules, but means code which imports VirtualizedList directly is affected the changes.
Changelog:
[Internal][Added] - Add VirtualizedList_EXPERIMENTAL (CellRenderMask Usage)
Reviewed By: lunaleaps
Differential Revision: D38020408
fbshipit-source-id: ad0aaa6791f3f4455e3068502a2841f3ffb40b41
Summary:
This diff forces a remeasure of the children of VirtualizedLists everytime the VirtualizedList is measured.
The goal is to ensure that nested VirtualizedList has the correct "scroll information" all the time, scroll information information is used by ViewabilityHelper.computeViewableItems method to determine if Items of the list are visible to the user.
This new code is controlled by the MC: rn_core:enable_virtualizedlist_remeasure_children_if_needed.
changelog: [internal] internal
// I used an internal changelog because this is under a MC
Reviewed By: lunaleaps
Differential Revision: D27003249
fbshipit-source-id: f9452ceb27683b0f595dd4bffdcced0ecf6bb0b5
Nick Gerleman
David Vacca