Problem

After plotting in user controls you have to call Render() to force a redraw.
This is not intuitive to new users and is easy to forget.

double[] dataX = new double[] {1, 2, 3, 4, 5};
double[] dataY = new double[] {1, 4, 9, 16, 25};
formsPlot1.plt.PlotScatter(dataX, dataY);
formsPlot1.Render(); // <-- you must do this

Solution?

Add a delegate to the Plot module:

public delegate void PlottablesUpdated();
public PlottablesUpdated PlottablesUpdatedHandler;

Invoke the delegate whenever the list of plottables is modified:

PlottablesUpdatedHandler?.Invoke();

User control constructors would wire it together like this:

plt.PlottablesUpdatedHandler = () => Render();

Thoughts

• There may be a slight performance hit since adding 5 scatter plots will cause 5 renders
• Automatic rendering can be disabled with formsPlot1.plt.PlottablesUpdatedHandler = null