[SOLVED] Create chart with number of series known at runtime
lazarus / 55-TAChart

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tudi_x · 2014-10-14 20:43

I am trying to write a procedure in which a chart is to be created
based on the number of columns in a database table (let us say table
has three columns, first two columns have values for Y series one and
two and the third column for X series).
Basically I can have charts that would have a variable number of (Y)
series.

Please advise how could I create these line series at run time.

Thank you

(Lazarus 1.2.4 32 bit on Windows 7 64 bit)

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wp · 2014-10-14 22:42

I am assuming your dataset contains five fields named "x", "y1", "y2",
"y3", "y4". The dataset is linked to a Datasource.

Add a DbChartSource to the form, link it to the DataSource.
Add a button which adds a new series to the chart:
Code: [Select]procedure TForm1.Button1Click(Sender: TObject);
begin
  // of course, you should use a more sophisticated logic here...
  case Chart1.SeriesCount of
    0: AddSeries('y1');
    1: AddSeries('y2');
    2: AddSeries('y3');
    3: AddSeries('y4');
  end;
end;

The method "AddSeries" adds a series at runtime; it copies the data
from the DBChartsource to the internal ListSource of the series; you
could also work with the DBChartSource directly but this requires to
load the data from the server with each change of data parameters:

Code: [Select]const
  COLORS: Array[0..3] of TColor = (clBlue, clRed, clGreen,
clFuchsia);  // a color for each series

procedure TForm1.AddSeries(AFieldName: String);
var
  series: TLineSeries;
begin
  DBChartSource1.FieldX := 'x';
  DBChartSource1.FieldY := AFieldName;
  DBChartSource1.DataSource := DataSource1;

  series := TLineseries.Create(self);  // or you could create a bar
series by "TBarSeries.Create", etc.
  series.SeriesColor := COLORS[Chart1.SeriesCount];
  series.ListSource.CopyFrom(DBChartSource1);
  series.Title := AFieldName;  // for the legend
  // set other properties here...
  Chart1.AddSeries(series);
end;

Since the table data are copied to the series the table can be closed
afterwards.

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tudi_x · 2014-10-16 01:47

Thank you for putting me in the right direction.