Flex's AreaChart bug

Question

What's up with Flex's AreaChart bug, does anybody know how to fix it? It causes ones tooltips to display the wrong value for minFields.

I.e. for:

<mx:AreaSeries yField="TotalVariableCost" minField="TotalFixedCost" displayName="Total Cost">

It will show:

Total Cost
high: TotalVariableCost
low: TotalVariableCost

As opposed to:

Total Cost
high: TotalVariableCost
low: TotalFixedCost

This bug is suppose to be in lines 2058 to 2083 of AreaSeries.as - but that stuff is way beyond my comprehension.

--Stephen

Answer 1

Yep, it's a bug in AreaSeries. Due to the stupid way that flex charts are designed, the only real way to fix it is to set a custom dataTipFunction on the AreaChart.

Here's a copy of the relevant code with the bug fixed:

/**
 * Create a data tip function for the given AreaSeries. Uses a copy of
 * the formatDataTip code from AreaSeries with the minValue bug fixed.
 * 
 * @param series
 * @return a data tip function
 * 
 */
private function createAreaSeriesTipFunc(series:AreaSeries):Function {
   var displayName:String = series.displayName;
   var dataTransform:DataTransform = series.dataTransform;
   var xField:String = series.xField;
   var minField:String = series.minField;

   // formatDataTip relies on AreaSeries member data so simulate that
   // with a closure to minimize code modifications

   return function(hd:HitData):String {
      var dt:String = "";
      var n:String = displayName;
      if (n && n != "")
         dt += "<b>"+ n + "</b><BR/>";

      var xName:String = dataTransform.getAxis(CartesianTransform.HORIZONTAL_AXIS).displayName;
      if (xName == "")
         xName = xField;
      if (xName != "")
         dt += "<i>" + xName + ": </i>";

      var item:AreaSeriesItem = AreaSeriesItem(hd.chartItem);
      var lowItem:AreaSeriesItem = (minField != "") ?
         item :
         null;
      dt += dataTransform.getAxis(CartesianTransform.HORIZONTAL_AXIS).formatForScreen(item.xValue) + "\n";

      var yName:String = dataTransform.getAxis(CartesianTransform.VERTICAL_AXIS).displayName;

      if (!lowItem)
      {
         if (yName != "")
            dt += "<i>" + yName + ":</i> ";
         dt += dataTransform.getAxis(CartesianTransform.VERTICAL_AXIS).formatForScreen(item.yValue) + "\n";
      }
      else
      {
         if (yName != "")
            dt += "<i>" + yName + " (high):</i> ";
         else
            dt += "<i>high: </i>";
         dt += dataTransform.getAxis(CartesianTransform.VERTICAL_AXIS).formatForScreen(item.yValue) + "\n";

         if (yName != "")
            dt += "<i>" + yName + " (low):</i> ";
         else
            dt += "<i>low:</i> ";
         dt += dataTransform.getAxis(CartesianTransform.VERTICAL_AXIS).formatForScreen(lowItem.minValue) + "\n";
      }

      return dt;
   };
}

I just changed formatForScreen(lowItem.yValue) to formatForScreen(lowItem.minValue) in one place. You can use it like this:

<mx:AreaChart dataProvider="{chartData}" showDataTips="true" dataTipFunction="{createAreaSeriesTipFunc(areaSeries)}">
      <mx:series>
         <mx:AreaSeries id="areaSeries" yField="TotalVariableCost" minField="TotalFixedCost" displayName="Total Cost" />
      </mx:series>
</mx:AreaChart>