title: qml Chartview append to AreaSeries
body: <p>I am new to QML and took following examle as a learning base for ChartView.
  Later on I want to use similar methods to add data dynmically during runtime</p>
  <pre><code>    import QtQuick 2.2
      import QtQuick.Window 2.1
      import QtQuick.Controls 2.4
      import QtQuick.Layouts 1.0
      import QtQuick.Dialogs 1.0
      import QtCharts 2.15
  
  
  
      ChartView {
              id: chart
              anchors.fill: parent
              axes: [
                  ValueAxis{
                      id: xAxis
                      min: 1.0
                      max: 10.0
                  },
                  ValueAxis{
                      id: yAxis
                      min: 0.0
                      max: 10.0
                  }
              ]
          //onClicked: console.log(&quot;onClicked: &quot; + point.x + &quot;, &quot; + point.y);
          Component.onCompleted: {
                  var seriesCount = Math.round(Math.random()* 10);
                  for(var i = 0;i &lt; seriesCount;i ++)
                  {  
                      var series = chart.createSeries(ChartView.SeriesTypeLine, &quot;line&quot;+ i, xAxis, yAxis);
                      series.pointsVisible = true;
                      series.color = Qt.rgba(Math.random(),Math.random(),Math.random(),1);
                      series.hovered.connect(function(point, state){ console.log(point); }); // connect onHovered signal to a function
                      var pointsCount = Math.round(Math.random()* 20);
                      var x = 0.0;
                      console.log(&quot;MOIN: &quot; + series)
                      for (var p in series) console.log(p + &quot;: &quot; + series[p]);
                      for(var j = 0;j &lt; pointsCount;j ++)
                      {
                          x += (Math.random() * 2.0);
                          var y = (Math.random() * 10.0);
                          series.append(x, y);
                      }
                  }
              }
          }
  </code></pre>
  <p>Taken from <a href="https://stackoverflow.com/questions/47928276/qml-create-lineseries-at-runtime">QML, create LineSeries at runtime</a></p>
  <p>I wanted to change it to AreaSeries and updated folloewing line</p>
  <pre><code>  var series = chart.createSeries(ChartView.SeriesTypeArea, &quot;line&quot;+ i, xAxis, yAxis);
  </code></pre>
  <p>But I get following error message for line :</p>
  <pre><code> series.append(x, y);
  </code></pre>
  <p><strong>MainChart.qml:42: TypeError: Property 'append' of object QtCharts::DeclarativeAreaSeries(0x1d955d73900) is not a function</strong></p>
  <p>I listed all members of series and could not find any similar function like add or push.</p>
  <p>Does the AreaSeries not support adding points dynmically</p>
  <p>UPDATE: I am sure, this is not the perfect solution, but it works. I forgot to add the upperSeries. Unfortunately I creates 2 entries in the legend. Does anybody know how to improve</p>
  <pre><code>        var seriesA = chart.createSeries(ChartView.SeriesTypeArea, null , xAxis, yAxis);
          seriesA.upperSeries = chart.createSeries(ChartView.SeriesTypeLine, null, xAxis, yAxis);
  </code></pre>