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Thursday, October 22, 2015Where in earlier versions, the method for adding values to a chart was via multiple calls to TMSFMXChart.Series[x].AddSinglePoint(), the new virtual mode offers a faster solution that is more flexible and typically consumes less memory. This can of course make a welcome difference when creating applications for mobile devices.
To start using the new TMS FMX Chart virtual mode, two events need to be implemented:
In the first event, OnGetNumberOfPoints(), that is triggered for each series in the chart, the number of desired data points can be returned via the ANumberOfPoints parameter.
In this sample event handler, the number of points is set to 10000 for each series in the chart:
The second event, OnGetPoint() is used to return the value for each point in the chart series. Here comes the flexibility that these values can be retrieved directly from another data structure (even a database). In this sample example, we assume the values are in a dynamic array of 10000 values and for the sake of this example filled with random floating point values. This is the code that initializes two dynamic arrays that have the data for 2 series:
procedure TForm1.TMSFMXChart1GetNumberOfPoints(Sender: TObject; ASerie: TTMSFMXChartSerie; var ANumberOfPoints: Integer); begin ANumberOfPoints := 10000; end;
and now the event handler that sets the values for the virtual chart:
var data_arr_1, data_arr_2: array of double; begin SetLength(data_arr_1,10000); SetLength(data_arr_2,10000); for i := 0 to Length(data_arr) - 1 do begin data_arr_1[i] := random(100) / 33; data_arr_2[i] := random(200) / 25; end; end;
A final touch is to apply some settings that will let the Y-axis scale automatically adapt to the values in the series and define the number of visible points along the X-axis (in this case 100 points of 10000 simultaneously visible along the X-axis, other values are shown when the chart is horizontally scrolled). This is done with:
procedure TForm1.TMSFMXChart1GetPoint(Sender: TObject; ASerie: TTMSFMXChartSerie; AIndex: Integer; var APoint: TTMSFMXChartPointVirtual); begin case ASerie.Index of 0: if AIndex < Length(data_arr_1) then APoint.YValue := data_arr_1[AIndex] 1: if AIndex < Length(data_arr_2) then APoint.YValue := data_arr_2[AIndex] end; end;
TMSFMXChart1.Series.AutoYRange := arEnabled; TMSFMXChart1.Series.MaxX := 100; TMSFMXChart1.Series.AutoYRange := arEnabled; TMSFMXChart1.Series.MaxX := 100;
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