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Tagging Plottables with Custom Objects

Windows Forms controls have a Tag property to allow users to store arbitrary object references. ScottPlot controls and plottables intentionally do not have such a property. Plottables have public properties used to store styling and data configuration information, but storing additional unrelated state inside plottables is not advised.

Instead, users are encouraged to create their own data structures to pair plottables with the custom objects unique to their application. A Dictionary works well here, as the key can be the plottable object and the value can be whatever object the developer is interested in keeping track of. Here is a Windows Forms application demonstrating this concept:

public partial class Form1 : Form
    // this dictionary pairs plotted objects with custom objects
    readonly Dictionary<IPlottable, string> SpecialValues = new();
    public Form1()
        // create plottables and add them to a dictionary, paring each with a special value
        SpecialValues.Add(formsPlot1.Plot.AddVerticalLine(0, Color.Red), "apple");
        SpecialValues.Add(formsPlot1.Plot.AddVerticalLine(1, Color.Blue), "grape");
        SpecialValues.Add(formsPlot1.Plot.AddVerticalLine(2, Color.Yellow), "banana");
        // enable dragging for all draggables
        formsPlot1.Plot.GetPlottables().OfType<IDraggable>().ToList().ForEach(x => x.DragEnabled = true);
        // call a function whenever a draggable is dropped
        formsPlot1.PlottableDropped += FormsPlot1_PlottableDropped;

        // refresh the screen once on load
    private void FormsPlot1_PlottableDropped(object sender, EventArgs e)
        IPlottable draggedPlottable = (IPlottable)sender;
        if (!SpecialValues.ContainsKey(draggedPlottable))
        // get the custom object for this plottable out of the dictionary
        string specialValue = SpecialValues[draggedPlottable];
        MessageBox.Show($"You just dropped: {specialValue}");