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Generalize the math in vertical panel scrolling #755

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Merged
zonble merged 1 commit into from
Dec 5, 2025
Merged

Generalize the math in vertical panel scrolling #755

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43 changes: 23 additions & 20 deletions Packages/CandidateUI/Sources/CandidateUI/VerticalCandidateController.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -390,33 +390,36 @@ public class VerticalCandidateController: CandidateController {
guard let delegate = delegate else {
return
}
let selectedRow = tableView.selectedRow
let labelCount = keyLabels.count
let itemCount = delegate.candidateCountForController(self)

if newValue == UInt.max {
tableView.deselectAll(self)
return
}

if itemCount > labelCount {
var rowToScroll = Int(newValue)
// The cast is safe: at this point, newValue cannot be UInt.max.
let newRowIndex = Int(newValue)

if selectedRow != -1 && itemCount > 0 {
let firstVisibleRow = tableView.row(at: scrollView.documentVisibleRect.origin)
// If it's not single row movement, trigger forward page switching.
if newValue > selectedRow && (Int(newValue) - selectedRow) > 1 {
let lastVisibleRow = firstVisibleRow + labelCount - 1
rowToScroll = min(lastVisibleRow + labelCount, Int(itemCount) - 1)
}
// If it's not single row movement, trigger backward page switching.
if newValue < selectedRow && (selectedRow - Int(newValue)) > 1 {
rowToScroll = max(0, firstVisibleRow - labelCount)
}
}
let labelCount = keyLabels.count
let itemCount = delegate.candidateCountForController(self)

if rowToScroll < Int.max {
tableView.scrollRowToVisible(rowToScroll)
if itemCount > labelCount && labelCount > 0 {
let selectedRow = tableView.selectedRow
let pageIndex = newRowIndex / labelCount

if selectedRow == -1 || abs(newRowIndex - selectedRow) == 1 {
// Simply scroll to the row if never selected or if it's moving by one.
tableView.scrollRowToVisible(newRowIndex)
} else {
if newRowIndex > selectedRow {
// Moving forward: scroll to the last row of the page that contains newRowIndex.
let scrollTo = min((pageIndex + 1) * labelCount, Int(itemCount)) - 1
tableView.scrollRowToVisible(scrollTo)
} else if newRowIndex < selectedRow {
// Moving backward: scroll to the first row of the page that contains newRowIndex.
let scrollTo = pageIndex * labelCount
tableView.scrollRowToVisible(scrollTo)
} else {
// No change in the selected index; do nothing.
}
}
}
tableView.selectRowIndexes(
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