Somehow chart.WithLegend only supports arg of bool. Have to call GenericChartExtensions.WithLegend(trace, legendSetting) explicitly to get it working.

var boxPlot = box
.WithLegend(true)
.WithXAxis(xAxis)
.WithLayout(plotLayout)
.WithSize(plotWidth, plotHeight);
GenericChartExtensions.WithLegend(boxPlot, legendSetting);

It is hard for me to make out the problem because you are mixing some concepts here. Chart2D.Scatter does not create a trace - it creates a GenericChart which contains trace(s), a layout, a config, and display options. The reason is that plotly strictly separates the layout of a chart from traces. Traces are just the data and style options of a single trace (e.g., the marker style). Layout options on the other hand are styling options for the whole chart, no matter how many traces it has. A legend is exactly such an object - something that is displayed for one or more traces of the chart.

So you are always aiming to set the legend on the layout, or use a method that changes the layout part of a GenericChart, for which you have multiple options:

• F# core API (these return F# functions, which you'd need to call Invoke on from C#):

  • Layout.setLegend or Layout.updateLegendById - static methods on the Layout class:

    Plotly.NET/src/Plotly.NET/Layout/Layout.fs

    Line 1126 in 98a4d18

    static member setLegend(id: StyleParam.SubPlotId, legend: Legend) =
  • Chart.withLegend or Chart.withLegendStyle - static methods of the Chart API:

    Plotly.NET/src/Plotly.NET/ChartAPI/Chart.fs

    Line 2629 in 98a4d18

    static member withLegend(legend: Legend, [<Optional; DefaultParameterValue(null)>] ?Id: int) =
  • GenericChartExtensions provides multiple overloads, one of them only takes boolean and needs to be removed, but there are others as well, see here :

    Plotly.NET/src/Plotly.NET/CSharpLayer/GenericChartExtensions.fs

    Lines 610 to 613 in 98a4d18

    // Set the LayoutGrid options of a Chart

    [<CompiledName("WithLegend")>]

    member this.WithLegend(legend: Legend, [<Optional; DefaultParameterValue(null)>] ?Id: int) =

    this |> Chart.withLegend (legend, ?Id = Id)

• GenericChartExtensions in Plotly.NET.C#:

  • WithLegend or WithLegendStyle:

    Plotly.NET/src/Plotly.NET.CSharp/GenericChartExtensions.cs

    Line 377 in 98a4d18

    public static GenericChart WithLegend(