Added accessibility for Bubble charts. (ChartsOrg#1060)

Updated BubbleChartRenderer to mirror LineChartRenderer's nested
use of accessibilityOrderedElements to populate accessibleChartElements.
Minor updates to comments in LineChartRenderer.

Source/Charts/Renderers/BubbleChartRenderer.swift

@@ -19,6 +19,9 @@ import CoreGraphics
 
 open class BubbleChartRenderer: BarLineScatterCandleBubbleRenderer
 {
+    /// A nested array of elements ordered logically (i.e not in visual/drawing order) for use with VoiceOver.
+    private lazy var accessibilityOrderedElements: [[NSUIAccessibilityElement]] = accessibilityCreateEmptyOrderedElements()
+
     @objc open weak var dataProvider: BubbleChartDataProvider?
 
     @objc public init(dataProvider: BubbleChartDataProvider, animator: Animator, viewPortHandler: ViewPortHandler)
@@ -35,10 +38,32 @@ open class BubbleChartRenderer: BarLineScatterCandleBubbleRenderer
             let bubbleData = dataProvider.bubbleData
             else { return }
 
-        for set in bubbleData.dataSets as! [IBubbleChartDataSet] where set.isVisible
+        // If we redraw the data, remove and repopulate accessible elements to update label values and frames
+        accessibleChartElements.removeAll()
+        accessibilityOrderedElements = accessibilityCreateEmptyOrderedElements()
+
+        // Make the chart header the first element in the accessible elements array
+        if let chart = dataProvider as? BubbleChartView {
+            let chartDescriptionText = chart.chartDescription?.text ?? ""
+            let dataSetDescriptions = bubbleData.dataSets.map { $0.label ?? "" }
+            let dataSetDescriptionText = dataSetDescriptions.joined(separator: ", ")
+            let dataSetCount = bubbleData.dataSets.count
+            let
+            element = NSUIAccessibilityElement(accessibilityContainer: chart)
+            element.accessibilityLabel = chartDescriptionText + ". \(dataSetCount) dataset\(dataSetCount == 1 ? "" : "s"). \(dataSetDescriptionText)"
+            element.accessibilityFrame = chart.bounds
+            element.isHeader = true
+            accessibleChartElements.append(element)
+        }
+
+        for (i, set) in (bubbleData.dataSets as! [IBubbleChartDataSet]).enumerated() where set.isVisible
         {
-            drawDataSet(context: context, dataSet: set)
+            drawDataSet(context: context, dataSet: set, dataSetIndex: i)
         }
+
+        // Merge nested ordered arrays into the single accessibleChartElements.
+        accessibleChartElements.append(contentsOf: accessibilityOrderedElements.flatMap { $0 } )
+        accessibilityPostLayoutChangedNotification()
     }
 
     private func getShapeSize(
@@ -57,7 +82,7 @@ open class BubbleChartRenderer: BarLineScatterCandleBubbleRenderer
     private var _pointBuffer = CGPoint()
     private var _sizeBuffer = [CGPoint](repeating: CGPoint(), count: 2)
 
-    @objc open func drawDataSet(context: CGContext, dataSet: IBubbleChartDataSet)
+    @objc open func drawDataSet(context: CGContext, dataSet: IBubbleChartDataSet, dataSetIndex: Int)
     {
         guard let dataProvider = dataProvider else { return }
 
@@ -116,6 +141,20 @@ open class BubbleChartRenderer: BarLineScatterCandleBubbleRenderer
 
             context.setFillColor(color.cgColor)
             context.fillEllipse(in: rect)
+
+            // Create and append the corresponding accessibility element to accessibilityOrderedElements
+            if let chart = dataProvider as? BubbleChartView
+            {
+                let element = createAccessibleElement(withIndex: j,
+                                                      container: chart,
+                                                      dataSet: dataSet,
+                                                      dataSetIndex: dataSetIndex)
+                { (element) in
+                    element.accessibilityFrame = rect
+                }
+
+                accessibilityOrderedElements[dataSetIndex].append(element)
+            }
         }
     }
 
@@ -282,4 +321,51 @@ open class BubbleChartRenderer: BarLineScatterCandleBubbleRenderer
             high.setDraw(x: _pointBuffer.x, y: _pointBuffer.y)
         }
     }
+
+    /// Creates a nested array of empty subarrays each of which will be populated with NSUIAccessibilityElements.
+    /// This is marked internal to support HorizontalBarChartRenderer as well.
+    private func accessibilityCreateEmptyOrderedElements() -> [[NSUIAccessibilityElement]]
+    {
+        guard let chart = dataProvider as? BubbleChartView else { return [] }
+
+        let maxEntryCount = chart.data?.maxEntryCountSet?.entryCount ?? 0
+
+        return Array(repeating: [NSUIAccessibilityElement](),
+                     count: maxEntryCount)
+    }
+
+    /// Creates an NSUIAccessibleElement representing the smallest meaningful bar of the chart
+    /// i.e. in case of a stacked chart, this returns each stack, not the combined bar.
+    /// Note that it is marked internal to support subclass modification in the HorizontalBarChart.
+    private func createAccessibleElement(withIndex idx: Int,
+                                         container: BubbleChartView,
+                                         dataSet: IBubbleChartDataSet,
+                                         dataSetIndex: Int,
+                                         modifier: (NSUIAccessibilityElement) -> ()) -> NSUIAccessibilityElement
+    {
+        let element = NSUIAccessibilityElement(accessibilityContainer: container)
+        let xAxis = container.xAxis
+
+        guard let e = dataSet.entryForIndex(idx) else { return element }
+        guard let dataProvider = dataProvider else { return element }
+
+        // NOTE: The formatter can cause issues when the x-axis labels are consecutive ints.
+        // i.e. due to the Double conversion, if there are more than one data set that are grouped,
+        // there is the possibility of some labels being rounded up. A floor() might fix this, but seems to be a brute force solution.
+        let label = xAxis.valueFormatter?.stringForValue(e.x, axis: xAxis) ?? "\(e.x)"
+
+        let elementValueText = dataSet.valueFormatter?.stringForValue(e.y,
+                                                                      entry: e,
+                                                                      dataSetIndex: dataSetIndex,
+                                                                      viewPortHandler: viewPortHandler) ?? "\(e.y)"
+
+        let dataSetCount = dataProvider.bubbleData?.dataSetCount ?? -1
+        let doesContainMultipleDataSets = dataSetCount > 1
+
+        element.accessibilityLabel = "\(doesContainMultipleDataSets ? (dataSet.label ?? "")  + ", " : "") \(label): \(elementValueText)"
+
+        modifier(element)
+
+        return element
+    }
 }

Source/Charts/Renderers/LineChartRenderer.swift

@@ -674,7 +674,7 @@ open class LineChartRenderer: LineRadarRenderer
                     continue
                 }
 
-                // ---------------
+                // Accessibility element geometry
                 let scaleFactor: CGFloat = 3
                 let accessibilityRect = CGRect(x: pt.x - (scaleFactor * circleRadius),
                                                y: pt.y - (scaleFactor * circleRadius),
@@ -693,7 +693,6 @@ open class LineChartRenderer: LineRadarRenderer
 
                     accessibilityOrderedElements[i].append(element)
                 }
-                // ---------------
 
                 if !dataSet.isDrawCirclesEnabled
                 {