[SOLVED] dateTime values into datapoints editor
lazarus / 55-TAChart

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wittbo · 2018-01-03 15:18

I'm just experimenting with the TAChart components. I need a DateTime
value based X-Axis, for quick checking I would like to use the
datapoints editor of the ListChartSource component. Is it possible to
enter datetime values directly into the X column of the editor
(actually I don't have success, for example I entered '01/01/2018',
but the result was 0) or does is only accept numeric values?
Thanks for help.

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wp · 2018-01-03 17:44

The datapoints editor only accepts numbers in the X and Y columns. Of
course, TDate, TTime and TDateTime are numbers internally. The number
value of Jan 1 2018 for example is 43101. So, if you want to construct
X date values in 1-day intervals starting at Jan 1, you enter the
numbers 43101, 43102, 43103, etc. in the X column.

In r56940 I modified the ListChartSource to accept also date/time
values in the X and Y columns. You must change to  Lazarus trunk to
get this feature. Or you must patch your local Lazarus version
yourself with these two changes:

Open unit tachartutils.pas (from (lazarus)/components/tachart) and add
a function which, of course, must be declared also in the interface
part of the unit:Code: Pascal  [Select][+][-]window.onload =
function(){var x1 = document.getElementById("main_content_section");
if (x1) { var x = document.getElementsByClassName("geshi");for (var i
= 0; i function StrToFloatOrDateTimeDef(const AStr: String):
Double;begin  if    not TryStrToFloat(AStr, Result,
DefSeparatorSettings) and    not TryStrToFloat(AStr, Result) and   
not TryStrToDateTime(AStr, Result)  then    Result := 0.0;end;Then
open unit tasources.pas and find procedure
TListChartSourceStrings.Parse. Replace each one of the three calls to
StrToFloatDefSep by this new function,
StrToFloatOrDateTimeDef.Nevertheless, using the datapoints editor is
not really recommended. Better to write a few lines of code to add the
data points.

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wittbo · 2018-01-04 12:09

Thanks a lot for your answer. It was a good help.
Of course it will be better to write code in practice. But the
datapoints editor is quite good for experimenting during design time
with the effects of the hundreds (  ) of TChart Parameters, which are
rather complex for TAChart newbies like me.

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wp · 2018-01-04 13:36

Of course. But usually, your precise data are not needed at all just
to play with parameters and to see what they change. It is much easier
to use a TRandomChartsource for the design phase and replace it later
by the chart source with the real data. I once described this strategy
in a tutorial, http://wiki.lazarus.freepascal.org/TAChart_Tutorial:_St
acked_BarSeries#Designing_the_chart_with_random_data is section on the
design phase.