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Editorial Team
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Asked: 2026-05-29T10:39:51+00:00

I am using core plot to make a line graph for my iPhone app.

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I am using core plot to make a line graph for my iPhone app. So far I successfully made the line graph from my xml data.

Furthermore I added a text layer that shows the value (for example 40) once I select the cell
holding the value 40. For this, I use the function:

(CPTLayer *)dataLabelForPlot:(CPTPlot *)plot recordIndex:(NSUInteger)index

So now I want to have a vertical line on the graph to indicate the selected value (the 40). I tried adding CPTBarplot but somehow the bars show only at the beginning of the graph axis.
Is there a function from core plot like the above that will create a line indicator?

I would appreciate if someone can give me some hint how to solve this problem and thank you very much in advance.

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1 Answer

  1. Editorial Team

    You could use a scatter plot for that. There’s a point selection demo in the Mac CPTTestApp that draws a crosshair over the selected point. It would be trivial to modify that to only draw the vertical line.

    The -numberOfRecordsForPlot: datasource method returns the number of points in the selection indicator (5 for the crosshairs) or zero (0) if there is no current selection. The -numberForPlot:field:recordIndex: method returns the points in the indicator. The points are drawn in this order:

    1. Left
    2. Right
    3. Center (with plot symbol)
    4. Top
    5. Bottom

    The -symbolForScatterPlot:recordIndex: method controls the plot symbol in the center. You can eliminate this method if you don’t need any symbols on the indicator plot.

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