Custom Visual Highlighting/Selection stops working

Hi  ,

Custom Visual: highlights/selection stop working when Table/Matrix gets big

You’re not imagining it. What you’re seeing is a mix of (a) how highlights are delivered to custom visuals, (b) data reduction/windowing, and (c) rows that don’t carry real identities (nulls/totals/rolled-up rows).

What’s actually happening
Highlights only arrive when your visual opted in
With "supportsHighlight": true, the host may send categorical.values[i].highlights (same length as values; non-selected rows are null). That array is only guaranteed for cross-visual highlight scenarios, not for your own selection, and not in all table/matrix states. Microsoft Learn

Your visual probably isn’t receiving the selected row because of data reduction
By default, custom visuals receive at most ~1000 rows per query window (top reduction). If the user selects a row that’s outside the window your visual requested, the host can’t line up the selected index → the highlights array is omitted (or doesn’t mark any of your current window rows). Use a bigger dataReductionAlgorithm count and/or implement fetchMoreData to page until the selected row falls into your window. Microsoft Learn+2GitHub+2

Some rows don’t have real identities
Table/Matrix can surface totals, blanks, or grouped rows. Those can show placeholders (or no identity at all), so your fallback on categorical.categories[0].identity[] won’t map back to a real selection. (This is why things work on “small/simple” tables but fail once you add columns, nulls, or groupings.) There isn’t a single doc line that calls it “placeholders,” but identity issues with table mapping and selection are a well-trodden pain point in the SDK/GitHub threads. coacervo+1

Practical fixes (what I’d change)
Raise your row window + implement paging

In capabilities.json, bump the window:

"dataViewMappings": [{
"categorical": {
"dataReductionAlgorithm": { "top": { "count": 30000 } }
}
}]

Handle fetchMoreData() when a selection occurs but your current window shows no highlighted rows. Keep appending until you either see the selected row or the host returns “no more data.” Microsoft Learn

Add a stable surrogate key and bind it in both visuals
Put a not-null RowKey (e.g., surrogate id) in the Table/Matrix and also bind the same field into your custom visual’s categories. This gives the engine a clean join path for highlights/identities even when the model grows, and avoids null/total rows breaking identity mapping. (This is the most reliable long-term pattern.)

Treat highlights as cross-visual only; own your selection via Selection Manager

Keep your “read highlights” path only when highlights exists.

For your own clicks, store/restore ISelectionIds with ISelectionManager so a re-update() doesn’t wipe your state. (Highlights are not the echo channel for your own selection.) Microsoft Learn+1

Defend against identity-less rows

If a selected Table/Matrix row has no identity (blank/total), show a friendly “cannot comment on totals/blank rows” message or require the RowKey field.

Optionally filter the user’s Table to exclude totals/blank GTM/keys to guarantee identities.

Consider table mapping if you truly work row-by-row
If your visual is logically “row” oriented, table dataViewMapping can be simpler to reason about than categorical when you start paging. (Still doesn’t fix identity for totals/nulls, but it makes row scanning straightforward.) coacervo

// On click in Table/Matrix (cross-visual): your visual receives update()
const hasHighlights = values?.some(v => Array.isArray((v as any).highlights));
if (!hasHighlights) {
// Selected row might be outside our window → try to page
if (await this.host.fetchMoreData()) return; // host will call update() again
}

// When we *do* have highlights, compute selected indices
const selectedIdx = rows.filter((r,i) => values.some(v => v.highlights?.[i] != null));

// If still none: either totals/blank identity or selection not in our data
// → fall back to RowKey (if you bound it) or show a friendly message.

Did I answer your question? Mark my post as a solution! Appreciate your Kudos !!