TreeView<TItem> handled only Enter/Space on the chevron; the tree itself was
unreachable by keyboard. Implements the WAI-ARIA tree pattern:
- Roving tabindex on li[role=treeitem] — exactly one node is tabbable, so the
whole tree is a single Tab stop. Target resolved per render: last-focused node
while still visible -> SelectedKey -> first visible node. Browser focus follows
via a per-node ElementReference + FocusAsync in OnAfterRenderAsync, guarded by
the same JSException/JSDisconnectedException/InvalidOperationException triple
the context-menu focus already used (a no-op under bUnit).
- ArrowDown/ArrowUp move between VISIBLE nodes; ArrowRight expands a collapsed
branch else moves to first child; ArrowLeft collapses an expanded branch else
moves to parent; Home/End jump to first/last; Enter/Space activate through the
SAME path a click takes (OnContentClick / OnCheckboxToggle) so selection
semantics never diverge between input modes.
- ARIA: aria-level, aria-posinset, aria-setsize added; aria-selected now renders
true/false on selectable+checkbox trees and stays absent on non-selectable ones.
- Event scoping: @onkeydown:stopPropagation on the li, chevron, checkbox and
content slot, so nested nodes do not double-handle and consumer controls inside
NodeContent keep their own key handling. Browser scroll-on-Space/Arrow is
suppressed by a minimal NATIVE inline onkeydown on the root ul, targeted at
treeitems only — Blazor's preventDefault directive is all-or-nothing per
element, so on the li it would trap Tab and cancel Enter/Space on consumer
buttons. No CSP is configured, so the inline handler runs.
BuildVisibleNodes() mirrors RenderNode's visibility rules and must stay in step.
Tests: 31 new bUnit tests in TreeViewKeyboardNavigationTests; the 47 existing
TreeView tests are unchanged and still green. Docs: new keyboard/a11y section in
docs/components/TreeView.md.
Joseph Doherty