title: Flex: Positioning Plot Series item
body: <p>I have a chart with multiple series (Area and Plot). The Area series has 'xField' as 'timeStamp' and 'yField' as 'price'. The Plot Series has 'xField' as 'timeStamp' and no 'yField'.... ! Can I position the plot series though I do not have a corresponding 'yField' value ? Can I assign a default value to the 'yField' (say '10' for all...?) </p>
  
  <p>This is how I create my AreaChart initially. At this point, I have no idea whether to render events or not, so I do not attempt to create a 'plot series' at this point. </p>
  
  <pre><code>    //Note: 'AreaSeries' and 'PlotSeries' have different dataproviders
  var areaChart:AreaChart = new AreaChart();
  areaChart.width = width;
  areaChart.height = height;
  areaChart.showDataTips = true;
  
  var vAxis:LinearAxis = new LinearAxis();
  if(vAxisLblFunction != null){
      vAxis.labelFunction = vAxisLblFunction;
      areaChart.verticalAxis = vAxis;
  }
  
  var hAxis:CategoryAxis = new CategoryAxis();
  hAxis.categoryField = "timeStamp";
  areaChart.horizontalAxis = hAxis;
  areaChart.horizontalAxisRenderer = createHAxisRenderer(hAxis);
  
  var areaChartSeries:AreaSeries = new AreaSeries();
  areaChartSeries.yField = "price";
  areaChartSeries.displayName = "Stock Price";
  areaChartSeries.setStyle("form", "segment");
  
  var chartStroke:Stroke = new Stroke();
  chartStroke.color = 0xFF0000;
  chartStroke.weight = CHART_STROKE_WEIGHT;
  
  var chartColor:SolidColor = new SolidColor();
  chartColor.alpha = CHART_ALPHA;
  chartColor.color = 0x000000;
  areaChartSeries.setStyle("areaStroke", chartStroke);
  areaChartSeries.setStyle("areaFill", chartColor);
  chartSeriesArr.push(areaChartSeries);
  </code></pre>
  
  <p>Now, during run-time I want to plot some events as required.</p>
  
  <pre><code>var evtSer:PlotSeries = new PlotSeries();
  evtSer.dataProvider = devEventsAC;  //Assume that I get the 'eventsDataProvider' somehow at run-time
  evtSer.xField = "timeStamp";   //Notice there is no 'yField' to map here.
  //evtSer.dataFunction = eventSerDataFunc;  //Tried with a 'dataFunction' assigning default value of '10' to the 'yField'
  
  var fillColor:SolidColor = new SolidColor();
  fillColor.color = 0xA933DC;
  fillColor.alpha = 0.8;
  evtSer.setStyle("fill", fillColor);
  
  var strokeColor:SolidColorStroke = new SolidColorStroke();
  strokeColor.color = 0x9494B8;
  strokeColor.weight = 1;
  evtSer.setStyle("stroke", strokeColor);
  var chartSeriesArr:Array = trendPanel.areaChart.series;
  chartSeriesArr.push(evtSer);
  trendPanel.areaChart.series = chartSeriesArr;
  </code></pre>
  
  <p>So, my problem is that how do I plot the 'events' without a 'yField'. Is there a way to assign 'yField' value using the series's 'dataFunction' ?</p>
  
  <p>Here is my thought:</p>
  
  <ol>
  <li>In the 'dataFunction' we get a reference to the 'series' object. Using the series object get the 'parent' which is the chart and then get the series array for that chart.</li>
  <li>Now, get the 'yField' value fron the 'AreaSeries' and return it as the 'yField' value for the 'plot series'.</li>
  <li>But, if I have multiple events with same 'yField' value there is a very good chance that all the events plotted top of each other. (First I am not sure whether 1 &amp; 2 works here...)</li>
  </ol>
  
  <p>Second approach is using the 'CartesianDataCanvas'. Again, here it requires datapoints (x,y) which I don't have. </p>