Erasing a graph
lazarus / 55-TAChart

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greatUnknown · 2012-08-29 02:36

Is there a way of erasing a graph without using FreeAndNil?

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wp · 2012-08-29 07:02

Call Chart.ClearSeries. Note that this removes the series instances
from the chart. If you want to keep the series and delete only the
series data iterate through Chart.Series and call Clear for each
Series. Like this:

Code: [Select]for i:=0 to Chart.SeriesCount-1 do
  if Chart.Series[i] is TChartSeries then
    TChartSeries(Chart.Series[i]).Clear;

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Ask · 2012-08-29 07:22

Or, using for-each:
Code: [Select]for ch in Chart.Series do
  if ch is TChartSeries then
    TChartSeries(ch).Clear;

Note that the above only works with the list sources,
if you used other sources, they must be cleared by their own means.

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greatUnknown · 2012-08-29 23:22

Thank you for the general knowledge, but it didn't work [as Ask
predicted] in my specific case because I was
using a TUserDefinedChartSource.

I ended up, with TUserDefinedChartSource, saving 
...Source.pointsCount, setting pointsCount := 0, and forcing a redraw
using  ...Source.reset.  However, this is a polarGraph, with
closeCircle = false, so Draw uses polyline.  Polyline does not
like 0 points.  Solution: a descendent Draw with  if (pointsCount >0)
then inherited Draw did the trick.

Redrawing was simply a matter of resetting  ...Source.pointsCount :=
savedCount, followed by  ...Source.reset.

[EDIT] Forcing a redraw using  ...Source.reset is superfluous.  Just
changing pointsCount is sufficient.

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Ask · 2012-08-30 02:13

QuotePolyline does not like 0 pointsFixed in r38430.

QuoteJust changing pointsCount is sufficient.Yes, this is a correct
method for your case.