DrawColumns allocated four fresh IReadOnlyList<T>?[] sidecar arrays and
ColumnLayout allocated a fresh (float,float)[] EVERY draw call; worse,
OnEventColumns re-invoked every column's source Func a SECOND time (via
UiMarkupListColumn.RowCount()) just to recompute the same row count
DrawColumns had already materialized, and called ColumnLayout a second
time to recompute the same layout — on every single click/scroll event.
Columns is now a property with a custom setter that (re)sizes seven
instance-field caches to Columns.Count exactly once per assignment:
_cachedTextRows/_cachedColorRows/_cachedCheckRows/_cachedIconRows (the
per-column sidecar arrays), _cachedLayout (the column x/width array),
and _scratchIsAuto/_scratchFixedWidth (ComputeColumnLayout's own working
arrays, previously freshly allocated on every layout computation too).
DrawColumns writes into these caches instead of local arrays and records
_cachedRowCount; ComputeColumnLayout (the renamed, now-instance
ColumnLayout) writes into _cachedLayout in place instead of returning a
new array. OnEventColumns reads _cachedRowCount/_cachedLayout/the
per-column cached row arrays instead of re-invoking anything — this also
completes fix item 3's row-bound guard without a second RowCount() call.
UiMarkupListColumn.RowCount() stays as public API (still asserted by an
existing test) but is no longer called from UiMarkupList internally,
which is the "single row-count definition" the fix round asked for.
This does make OnEvent depend on at least one prior Draw call for
correct row/layout data (mirrors real frame order: draw every frame,
then handle input) — the four hit-test click tests that previously
fired OnEvent with no preceding Draw now draw once first, matching what
Scroll_OffsetIsRespectedBySubsequentHitTests already did.
New test: each column source Func increments its own call counter; one
Draw call invokes each exactly once, and five rounds of subsequent
click events invoke none of them again — shown to fail first (16 calls
instead of 1, from OnEventColumns's old RowCount()-per-column-per-event
re-invocation) before the caching change.
Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
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