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Thread: Using QwtlegendData to Display a new column in the legend

  1. #1
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    Default Using QwtlegendData to Display a new column in the legend

    Hi, I'm planning to add a plotPicker to my plot, and when the user selects a position on the plot I want to display the x and y values of a curve in its legend entry based on the plotPicker (basically I want to implement a cursor feature and display the values in the plotLegend).

    I'm planning to overload QwtPlotItem::legendData() to return the 2 new attributes to the legend from my plotCurves, but I'm not sure what I need to change in the legend once I have these two new attributes that lets me define how they'll be displayed once they've been received by legendData(). I was hoping to put them in something like a QLabel with a border to distinguish these entries from the icon and title legend data attributes if at all possible.

    If this isn't possible let me know if there's some other sort of separator I can use in the legend as I don't want to have something plain like just appending these values to the curve's title unless it's my only option.

    Thanks,
    TEAmerc

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    Default Re: Using QwtlegendData to Display a new column in the legend

    Well, in general you can overload QwtAbstractLegend::updateLegend() to do whatever you want with these additional attributes. You could even implement your own style of legend, like it is done in the stockchart example.
    But why not setting up a signal/slot connection between picker and legend - sounds more logical to me than passing those attributes as legend data ?

    Uwe

  3. The following user says thank you to Uwe for this useful post:

    TEAmerc (25th November 2015)

  4. #3
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    Default Re: Using QwtlegendData to Display a new column in the legend

    That would work too, I was originally thinking about setting up the signal/slot connection between the picker and the curve and letting the curve pass the information to the legend (I've already subclassed the QwtPlotCurve for other things so it would be a small change), but I'll have to subclass QwtAbstractLegend either way I guess so it won't really save me work. Also, with your way I won't have to call updateLegend every time to update it so I'll do it that way and look into making a custom legend like in the stockchart example.

    Thanks,
    TEAmerc

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