Stack Overflow error when trying to draw Legend

[andrew-baylis]

Describe the bug
WPF - using CartesianChart.
When the Legend is visible and any series has IsVisibleAtLegend = false, we get a stack overflow and crash.
Note that a PieChart works as expected with some series having IsVisibleAtLegend = fasle.

To Reproduce
Steps to reproduce the behavior:
WPF - using CartesianChart. LegendPosition is anything other than Hidden
Add a couple of series (e.g. Line Series, Scatter Series, Column Series)
In one of them, set IsVisibleAtLegend = false
When trying to draw the chart, a StackOverflowError occurs

Expected behavior
Legend draws properly

Desktop (please complete the following information):

• OS: Windows 11
• Version 2.0.0beta 400

[andrew-baylis]

Found that the issue is in the Measure method of CartesianChart.cs in LiveChartsCore.

        if (Legend is not null && (SeriesMiniatureChanged(Series, LegendPosition) || SizeChanged())) 
        {
            Legend.Draw(this);
            PreviousLegendPosition = LegendPosition;
            PreviousSeriesAtLegend = Series.Where(x => x.IsVisibleAtLegend).ToList();
            foreach (var series in PreviousSeriesAtLegend.Cast<ISeries>()) series.PaintsChanged = false;
            preserveFirstDraw = IsFirstDraw;
            SetPreviousSize();
            Measure();
            return;
        }

The check SeriesMiniatureChanged(Series, LegendPosition) will always return true if one or more of the series has IsVisibleAtLegend false as we compare the full list of series with the partial list containing only those that should appear.

One way to fix is to do:

        var seriesForLegend = Series.Where(x => x.IsVisibleAtLegend).ToList(); //AJB change 24 Sep 2022

        //if (Legend is not null && (SeriesMiniatureChanged(Series, LegendPosition) || SizeChanged())) //old version
        if (Legend is not null && (SeriesMiniatureChanged(seriesForLegend, LegendPosition) || SizeChanged()))
        {
            Legend.Draw(this);
            PreviousLegendPosition = LegendPosition;
            PreviousSeriesAtLegend = Series.Where(x => x.IsVisibleAtLegend).ToList();
            foreach (var series in PreviousSeriesAtLegend.Cast<ISeries>()) series.PaintsChanged = false;
            preserveFirstDraw = IsFirstDraw;
            SetPreviousSize();
            Measure();
            return;
        }

[beto-rodriguez]

Thanks for the report and the fix. it works!

this is fixed with the referenced commit and will be included in the next version of the library.