Removed ambiguity of _dataNotSet (Fixes #585)

We can just check for _data being null,
knowing that this is the situation defined as "no data"

Charts/Classes/Charts/BarChartView.swift

@@ -63,7 +63,7 @@ public class BarChartView: BarLineChartViewBase, BarChartDataProvider
     /// - returns: the Highlight object (contains x-index and DataSet index) of the selected value at the given touch point inside the BarChart.
     public override func getHighlightByTouchPoint(pt: CGPoint) -> ChartHighlight?
     {
-        if (_dataNotSet || _data === nil)
+        if _data === nil
         {
             print("Can't select by touch. No data set.", terminator: "\n")
             return nil

Charts/Classes/Charts/BarLineChartViewBase.swift

@@ -134,7 +134,7 @@ public class BarLineChartViewBase: ChartViewBase, BarLineScatterCandleBubbleChar
     {
         super.drawRect(rect)
 
-        if (_dataNotSet)
+        if _data === nil
         {
             return
         }
@@ -261,7 +261,7 @@ public class BarLineChartViewBase: ChartViewBase, BarLineScatterCandleBubbleChar
 
     public override func notifyDataSetChanged()
     {
-        if (_dataNotSet)
+        if _data === nil
         {
             return
         }
@@ -614,7 +614,7 @@ public class BarLineChartViewBase: ChartViewBase, BarLineScatterCandleBubbleChar
 
     @objc private func tapGestureRecognized(recognizer: UITapGestureRecognizer)
     {
-        if (_dataNotSet)
+        if _data === nil
         {
             return
         }
@@ -640,14 +640,14 @@ public class BarLineChartViewBase: ChartViewBase, BarLineScatterCandleBubbleChar
 
     @objc private func doubleTapGestureRecognized(recognizer: UITapGestureRecognizer)
     {
-        if (_dataNotSet)
+        if _data === nil
         {
             return
         }
 
         if (recognizer.state == UIGestureRecognizerState.Ended)
         {
-            if (!_dataNotSet && _doubleTapToZoomEnabled)
+            if _data !== nil && _doubleTapToZoomEnabled
             {
                 var location = recognizer.locationInView(self)
                 location.x = location.x - _viewPortHandler.offsetLeft
@@ -673,7 +673,7 @@ public class BarLineChartViewBase: ChartViewBase, BarLineScatterCandleBubbleChar
         {
             stopDeceleration()
 
-            if (!_dataNotSet && (_pinchZoomEnabled || _scaleXEnabled || _scaleYEnabled))
+            if _data !== nil && (_pinchZoomEnabled || _scaleXEnabled || _scaleYEnabled)
             {
                 _isScaling = true
 
@@ -763,7 +763,7 @@ public class BarLineChartViewBase: ChartViewBase, BarLineScatterCandleBubbleChar
         {
             stopDeceleration()
 
-            if _dataNotSet
+            if _data === nil
             { // If we have no data, we have nothing to pan and no data to highlight
                 return;
             }
@@ -943,7 +943,7 @@ public class BarLineChartViewBase: ChartViewBase, BarLineScatterCandleBubbleChar
 
         if (gestureRecognizer == _panGestureRecognizer)
         {
-            if _dataNotSet || !_dragEnabled ||
+            if _data === nil || !_dragEnabled ||
                 (self.hasNoDragOffset && self.isFullyZoomedOut && !self.isHighlightPerDragEnabled)
             {
                 return false
@@ -954,7 +954,7 @@ public class BarLineChartViewBase: ChartViewBase, BarLineScatterCandleBubbleChar
             #if !os(tvOS)
                 if (gestureRecognizer == _pinchGestureRecognizer)
                 {
-                    if (_dataNotSet || (!_pinchZoomEnabled && !_scaleXEnabled && !_scaleYEnabled))
+                    if _data === nil || (!_pinchZoomEnabled && !_scaleXEnabled && !_scaleYEnabled)
                     {
                         return false
                     }
@@ -1387,7 +1387,7 @@ public class BarLineChartViewBase: ChartViewBase, BarLineScatterCandleBubbleChar
     /// - returns: the Highlight object (contains x-index and DataSet index) of the selected value at the given touch point inside the Line-, Scatter-, or CandleStick-Chart.
     public func getHighlightByTouchPoint(pt: CGPoint) -> ChartHighlight?
     {
-        if (_dataNotSet || _data === nil)
+        if _data === nil
         {
             print("Can't select by touch. No data set.", terminator: "\n")
             return nil

Charts/Classes/Charts/ChartViewBase.swift

@@ -73,9 +73,6 @@ public class ChartViewBase: UIView, ChartDataProvider, ChartAnimatorDelegate
     /// description text that appears in the bottom right corner of the chart
     public var descriptionText = "Description"
 
-    /// flag that indicates if the chart has been fed with data yet
-    internal var _dataNotSet = true
-
     /// if true, units are drawn next to the values in the chart
     internal var _drawUnitInChart = false
 
@@ -197,7 +194,6 @@ public class ChartViewBase: UIView, ChartDataProvider, ChartAnimatorDelegate
                 return
             }
 
-            _dataNotSet = false
             _offsetsCalculated = false
             _data = newValue
 
@@ -212,7 +208,6 @@ public class ChartViewBase: UIView, ChartDataProvider, ChartAnimatorDelegate
     public func clear()
     {
         _data = nil
-        _dataNotSet = true
         _indicesToHighlight.removeAll()
         setNeedsDisplay()
     }
@@ -297,8 +292,8 @@ public class ChartViewBase: UIView, ChartDataProvider, ChartAnimatorDelegate
 
         let frame = self.bounds
 
-        if (_dataNotSet || _data === nil || _data.yValCount == 0)
-        { // check if there is data
+        if _data === nil
+        {
 
             CGContextSaveGState(context)
 

Charts/Classes/Charts/HorizontalBarChartView.swift

@@ -175,7 +175,7 @@ public class HorizontalBarChartView: BarChartView
 
     public override func getHighlightByTouchPoint(pt: CGPoint) -> ChartHighlight?
     {
-        if (_dataNotSet || _data === nil)
+        if _data === nil
         {
             print("Can't select by touch. No data set.", terminator: "\n")
             return nil

Charts/Classes/Charts/PieChartView.swift

@@ -50,7 +50,7 @@ public class PieChartView: PieRadarChartViewBase
     {
         super.drawRect(rect)
 
-        if (_dataNotSet)
+        if _data === nil
         {
             return
         }
@@ -81,7 +81,7 @@ public class PieChartView: PieRadarChartViewBase
         super.calculateOffsets()
 
         // prevent nullpointer when no data set
-        if (_dataNotSet)
+        if _data === nil
         {
             return
         }

Charts/Classes/Charts/PieRadarChartViewBase.swift

@@ -74,7 +74,7 @@ public class PieRadarChartViewBase: ChartViewBase
 
     public override func notifyDataSetChanged()
     {
-        if (_dataNotSet)
+        if _data === nil
         {
             return
         }

Charts/Classes/Charts/RadarChartView.swift

@@ -138,7 +138,7 @@ public class RadarChartView: PieRadarChartViewBase
 
     public override func notifyDataSetChanged()
     {
-        if (_dataNotSet)
+        if _data === nil
         {
             return
         }
@@ -164,7 +164,7 @@ public class RadarChartView: PieRadarChartViewBase
     {
         super.drawRect(rect)
 
-        if (_dataNotSet)
+        if _data === nil
         {
             return
         }