Notification when adding a new series to a TChart
lazarus / 55-TAChart

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wp · 2011-07-05 16:39

As discussed in another thread I am writing a TChartListbox for being
able to show/hide series of a TChart. In order to get notified for
changes in the series I added a TListener to the component.

Code: [Select]  FListener := TListener.Create(@FChart,
@SeriesChanged);

"SeriesChanged" presently just calls "Populate" which reads all series
into the listbox:

Code: [Select]procedure TChartListbox.Populate;
var
  i : integer;
begin
  try
    FreeAndNil(FLegendItems);
    Items.BeginUpdate;
    Items.Clear;
    if (FChart <> nil) then begin
      FLegendItems := GetLegendItems;
      for i:=0 to FLegendItems.Count-1 do begin
        Items.AddObject('', FLegendItems[i]);
        Checked[i] :=
TCustomChartSeries(FLegendItems[i].Owner).Active;
      end;
    end;
  finally
    Items.EndUpdate;
  end;
end

There is a button on the form which adds a new series with random data
to the chart.

Code: [Select]procedure TForm1.Button1Click(Sender:TObject);
var
  ser : TLineSeries;
begin
  RandomChartSource.RandSeed := random(65000);
  ser := TLineSeries.Create(Chart);
  ser.Source := RandomChartSource;
  ser.SeriesColor := rgbToColor(random(255), random(256),
random(256));
  ser.Title := Format('Series %d', [Chart.SeriesCount]);
  Chart.AddSeries(ser);
end;

The new series appeas in the chart immediately. In the listbox,
however, it appears only after clicking the button for a second time.
There must be something in the listening/broadcasting mechanism which
I do not understand.

What am I doing wrong?

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Ask · 2011-07-05 17:09

Try r31568.

The Broadcaster will react on any visible change to a chart, from
zooming to adding a point.
Unfortunately, there are quite a few potential events that may change
legend appearance --
such as changing SeriesColor etc., so filtering relevant events seems
impossible to me.

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wp · 2011-07-06 09:03

Yes, now the listbox reacts immediately.

Does the broadcaster transmit supplementary information on what has
been changed in the chart? I try to avoid building the listbox items
each time data were added to a series by means of AddXY.

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Ask · 2011-07-06 10:03

Notification event receives an argument (Sender), containing the
object which initiated the change.
In particular, adding points results in Sender being equal to the
corresponding chart source.

However, I am not sure there is a robust way to distinguish which
changes
will accept the legend look -- for example, somebody can write a
legend item
which encodes the size of the series.