Capture Showpoint from chart series
lazarus / 55-TAChart

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madepabloh · 2014-08-23 17:34

I have a chart with multiple line series created on runtime, which
list is showed in a ChartListBox.

Now, I would like to capturethe properties of the serie selected in
the charlist box (by its "onitemclick" event).
The idea is to show all those options in different components what
could be modified by the usser and inmediatly appied to the selected
serie.

Foe example, for to start with something, i added 2 label and 2
checkbuttons. I would like to capture the series title and tag, as
well as the ShowPoints and Showlines options of that series.

I tried this code, but it does not work for the showpoints and
showlines options but for name and tag. What should be the correct way
to do it? I would like to allow the user to modify many other options
on runtime, such as line color, line width, point symbol, color, size,
label, label fonts, etc.

Code: [Select]procedure TMain.ChartListbox1ItemClick(ASender: TObject;
AIndex: Integer);
begin
  Label3.Caption := ChartListBox1.Series[AIndex].Title;
  Label2.Caption := InttoStr(ChartListBox1.Series[AIndex].Tag);
  Label1.Caption := ChartListBox1.Series[AIndex].Name;
  Checkbox2.Checked := ChartListBox1.Series[AIndex].showpoints;
  Checkbox1.Checked := ChartListBox1.Series[AIndex].ShowLines;
end;
     
The code not compiles for the last two functions. Obviously, this is
not the correct way to do it, but i can´f figure out the correct
method, thaing into account that it works for the other options of the
serie i tried.

Thanks

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wp · 2014-08-23 17:48

This is because the "Series[]" returned from the chartlistbox is the
least specialized version in the series class hierarchy: a
TCustomChartSeries which exposes only a few properties common to all
series.

Since your series are TLineSeries you should use a type-cast to get
access the special properites of this series type. For safety you
should check by means of the "is" operator whether the series really
is a TLineSeries. In a cubic-spline series, for examples, symbols and
lines are turned on and off in a different way. You can take advantage
of this to distinguish such cases:

Code: [Select]  if ChartListbox1.Series[AIndex] is TLineSeries then
    Checkbox2.Checked :=
TLineSeries(ChartListBox1.Series[AIndex]).showpoints
  else
  if ChartListbox1.Series[AIndex] is TCubicSplineSeries then
    Checkbox2.Checked :=
TCubicSplineSeries(ChartListbox1.Series[AIndex]).Pointer.Visible;

  if ChartListbox1.Series[AIndex] is TLineSeries then
    Checkbox1.Checked :=
TLineSeries(ChartListBox1.Series[AIndex]).ShowLines
  else
  if ChartListbox1.Series[AIndex] is TCubicSplineSeries then
    Checkbox2.Checked :=
TCubicSplineSeries(ChartListbox1.Series[AIndex]).Pen.Visible;

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madepabloh · 2014-08-23 18:00

Thanks @wp,

Yes, i was wonder why if the properties appear under the objects
inspector they are not able to be captured in the same way than the
other properties.

I will check. Thanks!!

Edited:
It works perfect. Thanks!!