OxyPlot axis always null

I have problem with OxyPlot Library. I do npt understand why it's working so weird.

For example why "double temp1 = XAxis.Transform(this.MyMemento._rectangle.MaximumX);" is alway NaN?

namespace OxyRectangle

{

///

/// Interaction logic for MainWindow.xaml

///

public partial class MainWindow : Window

{

public MainWindow()

{

InitializeComponent();

this.DataContext = new RectangleScale();

}

public class RectangleScale

{

public PlotModel PlotModel { get; set; }

RectangleAnnotation Rectum;

private LinearAxis XAxis;

private LinearAxis YAxis;

public Memento MyMemento { get; set; }

public RectangleScale()

{

PlotModel = new PlotModel();

XAxis = new LinearAxis

{

Position = AxisPosition.Bottom

};

YAxis = new LinearAxis

{

Position= AxisPosition.Left,

IsPanEnabled=false

};

Rectum = new RectangleAnnotation();

SetRectum(Rectum, 1, 1, 10, 10);

MyMemento = new Memento(Rectum);

PlotModel.Axes.Add(XAxis);

PlotModel.Axes.Add(YAxis);

PlotModel.Annotations.Add(Rectum);

ChangeAxis(PlotModel, 100, 200);

ConvertOldRectangle(Rectum);

PlotModel.InvalidatePlot(true);

}

public void SetRectum(RectangleAnnotation rectangle, double xmin, double ymin, double xmax, double ymax)

{

rectangle.MinimumX = xmin;

rectangle.MinimumY = ymin;

rectangle.MaximumX = xmax;

rectangle.MaximumY = ymax;

}

public void ChangeAxis(PlotModel _plotmodel,int minimum,int maximum)

{

_plotmodel.Axes.Clear();

LinearAxis XAxis = new LinearAxis

{

Position = AxisPosition.Bottom,

Minimum=minimum,

Maximum=maximum

};

LinearAxis YAxis = new LinearAxis

{

Position = AxisPosition.Left,

Minimum=minimum,

Maximum=maximum,

IsPanEnabled = false

};

_plotmodel.Axes.Add(XAxis);

_plotmodel.Axes.Add(YAxis);

_plotmodel.InvalidatePlot(true);

}

public void ConvertOldRectangle(RectangleAnnotation _rectangle)

{

PlotModel.InvalidatePlot(true);

double temp1 = XAxis.Transform(this.MyMemento._rectangle.MaximumX);

double temp2 = XAxis.Transform(this.MyMemento._rectangle.MinimumX);

double temp3 = YAxis.Transform(this.MyMemento._rectangle.MaximumY);

double temp4 = YAxis.Transform(this.MyMemento._rectangle.MinimumY);

_rectangle.MaximumX = XAxis.InverseTransform(temp1);

_rectangle.MinimumX = XAxis.InverseTransform(temp2);

_rectangle.MaximumY = YAxis.InverseTransform(temp3);

_rectangle.MinimumY = YAxis.InverseTransform(temp4);

}

public void Revert()

{

Rectum = this.MyMemento._rectangle;

}

public class Memento

{

public readonly RectangleAnnotation _rectangle;

public Memento(RectangleAnnotation rectangle)

{

_rectangle = rectangle;

}