Hello,

I think I found a bug when I use AreaSeries and a custom DataPoint.
If I'm wrong please forgive me, this is the first alert I send.
I want to highlight this behaviour not happens with LineSeries.

Steps to reproduce

1. Define a class named CustomDataPoint, with 3 fields: double X, double Y and int Z;
2. create an array of CustomDataPoint and populate it;
3. create an AreaSeries, then populate with an array of CustomDataPoint;
4. associate the AreaSeries to a Plot, than look the results.

Platform

OxyPlot version: v2.1.2
OxyPlot RunTime version: v4.0.30319
.NET version: v4.7.2

Expected behaviour

Define a custom DataPoint named... CustomDataPoint, ok, in that way:

public class CustomDataPoint : IDataPointProvider
    {
        public double X { get; }
        public double Y { get; }
        public int Orig { get; }

        public CustomDataPoint(double x, double y, int z)
        {
            X = x;
            Y = y;
            Z= z;
        }

        public DataPoint GetDataPoint()
        {
            return new DataPoint(X, Y);
        }
    }

Than, we create an AreaSeries variable with a specific TrackerFormatString, in that way:

AreaSeries LSTest = new AreaSeries() { Title="Hello Oxy!", Color = OxyColor.FromRgb(125,70,30) };
LSTest.TrackerFormatString = "Y: {4:0.#####}\nX: {2:0.#####}\nZ: {Z}";

Simple, isn't it?
Than, in the function/method we want to use it, create an array of CustomDataPoint in that way:

CustomDataPoint[] CdpTest = new CustomDataPoint[1000];
for(int i=0; i<1000; i++){
   CdpTest[i] = new CustomDataPoint(FunctForX(x), FunctForY, i);
}
LSTest.ItemsSource = CdpTest;
PlotTest.Series.Add(LSTest);

So, when we click on the curve, we'll have in the Tooltip 3 infos:

• the X value;
• the Y value;
• the Z value, an incremental number in the interval [0 ... 999].

Results

We have that:

How to solve

You can solve it using LineSeries, not AreaSeries.

AreaSeries is a powerful tool when you have to compare 2 series: i.e. Baseline vs Current.
Don't trash it. Love it. Bugfix it.