The following exception is thrown when using enabling a Trackball with a CategoryAxis x-axis.

════════ Exception caught by gesture library ═══════════════════════════════════
The following RangeError was thrown while dispatching a pointer event:
RangeError (index): Invalid value: Not in range 0..6, inclusive: 170

When the exception was thrown, this was the stack
#0 List.[] (dart:core-patch/growable_array.dart:147:60)
#1 _TrackballPainter._generateAllPoints
package:syncfusion_flutter_charts/…/user_interaction/trackball_painter.dart:631
#2 TrackballBehavior.show
package:syncfusion_flutter_charts/…/user_interaction/trackball.dart:206
#3 TrackballBehavior.onTouchDown
package:syncfusion_flutter_charts/…/user_interaction/trackball.dart:230
#4 _ContainerArea._bindInteractionWidgets.
package:syncfusion_flutter_charts/…/base/chart_base.dart:1636
...
Event: PointerDownEvent#19ffd(position: Offset(246.1, 405.0), timeStamp: 32:30:22.992000, pointer: 15, kind: touch, buttons: 1, down: true, pressure: 0.6, pressureMin: 0.0, pressureMax: 3.2, size: 0.1, radiusMajor: 91.8, radiusMinor: 91.8)
position: Offset(246.1, 405.0)
Target: RenderPointerListener#26a18 relayoutBoundary=up1
parentData: not positioned; offset=Offset(0.0, 0.0) (can use size)
constraints: BoxConstraints(0.0<=w<=391.4, 0.0<=h<=425.0)
size: Size(391.4, 425.0)
behavior: deferToChild
listeners: down, move, up
════════════════════════════════════════════════════════════════════════════════

This appears to be due to the following code in trackball_painter.dart (line 630):

} else if (axis is CategoryAxis) {
                        x = axis._visibleLabels[xValue.round()].text;
                      }

The _visibleLabel property of axis contains only 6 values due to the large number of x-values in my CategoryAxis, and these being truncated to display nicely.

I suspect this can be fixed by changing the code to:

} else if (axis is CategoryAxis) {
                        x = axis._labels[xValue.round()].text;
                      }