Optimize TopTotalsCell to add rows only when the cell loads

TopTotalsCell was calling addRows on every configuration of cell which in turn created and added a hierarchy of UIStackView-based views.

Optimizing TopTotalsCell to only add rows once and then make manipulations on existing rows.

Author: staskus

WordPress/Classes/ViewRelated/Stats/Extensions/UITableViewCell+Stats.swift

@@ -71,3 +71,84 @@ extension UITableViewCell {
     }
 
 }
+
+ extension UITableViewCell {
+    struct StatsTotalRowConfiguration {
+        let limitRowsDisplayed: Bool
+        let rowDelegate: StatsTotalRowDelegate?
+        let referrerDelegate: StatsTotalRowReferrerDelegate?
+        let viewMoreDelegate: ViewMoreRowDelegate?
+    }
+
+    func addDefaultTotalRows(toStackView rowsStackView: UIStackView) {
+        for _ in 0..<StatsDataHelper.maxRowsToDisplay {
+            let row = StatsTotalRow.loadFromNib()
+            rowsStackView.addArrangedSubview(row)
+        }
+
+        let emptyRow = StatsNoDataRow.loadFromNib()
+        rowsStackView.addArrangedSubview(emptyRow)
+
+        let viewMoreRow = ViewMoreRow.loadFromNib()
+        rowsStackView.addArrangedSubview(viewMoreRow)
+    }
+
+     func configureTotalRows(_ dataRows: [StatsTotalRowData],
+                             inStackView rowsStackView: UIStackView,
+                             forType statType: StatType,
+                             configuration: StatsTotalRowConfiguration) {
+
+        guard !dataRows.isEmpty else {
+            configureForNoData(inStackView: rowsStackView, forType: statType)
+            return
+        }
+
+        let numberOfRowsToAdd = calculateNumberOfRowsToAdd(from: dataRows, withConfiguration: configuration)
+
+        rowsStackView.arrangedSubviews.enumerated().forEach { index, view in
+            configure(view: view, at: index, in: dataRows, numberOfRowsToAdd: numberOfRowsToAdd, configuration: configuration)
+        }
+    }
+
+    private func configureForNoData(inStackView rowsStackView: UIStackView, forType statType: StatType) {
+        rowsStackView.arrangedSubviews.forEach { view in
+            if let emptyRow = view as? StatsNoDataRow {
+                emptyRow.isHidden = false
+                emptyRow.configure(forType: statType)
+            } else {
+                view.isHidden = true
+            }
+        }
+    }
+
+     private func calculateNumberOfRowsToAdd(from dataRows: [StatsTotalRowData], withConfiguration configuration: StatsTotalRowConfiguration) -> Int {
+        if configuration.limitRowsDisplayed {
+            return min(dataRows.count, StatsDataHelper.maxRowsToDisplay)
+        }
+        return dataRows.count
+    }
+
+     private func configure(view: UIView, at index: Int, in dataRows: [StatsTotalRowData], numberOfRowsToAdd: Int, configuration: StatsTotalRowConfiguration) {
+        switch view {
+        case let view as StatsNoDataRow:
+            view.isHidden = true
+        case let view as ViewMoreRow:
+            configureViewMoreRow(view, at: index, in: dataRows, withConfiguration: configuration)
+        case let view as StatsTotalRow where index < dataRows.count:
+            view.isHidden = false
+            let dataRow = dataRows[index]
+            view.configure(rowData: dataRow, delegate: configuration.rowDelegate, referrerDelegate: configuration.referrerDelegate)
+            view.showSeparator = index != (numberOfRowsToAdd - 1)
+        default:
+            view.isHidden = true
+        }
+    }
+
+     private func configureViewMoreRow(_ viewMoreRow: ViewMoreRow, at index: Int, in dataRows: [StatsTotalRowData], withConfiguration configuration: StatsTotalRowConfiguration) {
+        let shouldShowViewMore = configuration.limitRowsDisplayed && dataRows.count > StatsDataHelper.maxRowsToDisplay
+        viewMoreRow.isHidden = !shouldShowViewMore
+        if shouldShowViewMore {
+            viewMoreRow.configure(statSection: dataRows.first?.statSection, delegate: configuration.viewMoreDelegate)
+        }
+    }
+}

WordPress/Classes/ViewRelated/Stats/Shared Views/TopTotalsCell.swift

@@ -42,6 +42,12 @@ class TopTotalsCell: StatsBaseCell, NibLoadable {
     private weak var postStatsDelegate: PostStatsDelegate?
     private typealias Style = WPStyleGuide.Stats
 
+    override func awakeFromNib() {
+        super.awakeFromNib()
+
+        addDefaultTotalRows(toStackView: rowsStackView)
+    }
+
     // MARK: - Configure
 
     func configure(itemSubtitle: String? = nil,
@@ -71,41 +77,30 @@ class TopTotalsCell: StatsBaseCell, NibLoadable {
         self.forDetails = forDetails
 
         if !forDetails {
-            addRows(dataRows,
-                    toStackView: rowsStackView,
-                    forType: siteStatsPeriodDelegate != nil ? .period : .insights,
+            if rowsStackView.arrangedSubviews.isEmpty {
+                addDefaultTotalRows(toStackView: rowsStackView)
+            }
+            configureTotalRows(
+                dataRows,
+                inStackView: rowsStackView,
+                forType: siteStatsPeriodDelegate != nil ? .period : .insights,
+                configuration: .init(
                     limitRowsDisplayed: limitRowsDisplayed,
                     rowDelegate: self,
                     referrerDelegate: self,
-                    viewMoreDelegate: self)
-
+                    viewMoreDelegate: self
+                )
+            )
             initChildRows()
+        } else {
+            rowsStackView.arrangedSubviews.forEach { $0.removeFromSuperview() }
         }
 
         setSubtitleVisibility()
         applyStyles()
         prepareForVoiceOver()
     }
 
-    override func prepareForReuse() {
-        super.prepareForReuse()
-
-        rowsStackView.arrangedSubviews.forEach { subview in
-
-            // Remove granchild rows
-            if let row = subview as? StatsTotalRow {
-                removeChildRowsForRow(row)
-            }
-
-            // Remove child rows
-            if let childView = subview as? StatsChildRowsView {
-                removeRowsFromStackView(childView.rowsStackView)
-            }
-        }
-
-        removeRowsFromStackView(rowsStackView)
-    }
-
     private enum Metrics {
         static let topAccessoryViewSpacing: CGFloat = 32.0
     }