How do I get the focus of a canvas that is part of a UserControl

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WPF

Hello friends, good afternoon, look I have a user control in which I add two circles from code (emulating a Dial) that look like this:

public partial class KnobControl : UserControl
    {
        Canvas CnvCirculoP ;//Contiene al circulo pequeño
        Canvas CnvCirculoG; // Contiene al circulo grande

public KnobControl()
        {
            InitializeComponent();

            CnvCirculoP.MouseMove += new MouseEventHandler(CircularIndicator_MouseMove);

            CnvCirculoP.MouseLeftButtonDown += new MouseButtonEventHandler(CircularIndicator_MouseLeftButtonDown);

            CnvCirculoP.MouseLeftButtonUp += new MouseButtonEventHandler(CircularIndicator_MouseLeftButtonUp);


            Dibujar ();
        }

private void Dibujar()
{
.
.
.
   LayoutGrid.Children.Add(CnvCirculoG);        
   LayoutGrid.Children.Add(CnvCirculoP);
}

The events are as follows:

void CircularIndicator_MouseLeftButtonUp(object sender, MouseButtonEventArgs e)
        {
            this.isKnobRotating = false;
        }

        void CircularIndicator_MouseLeftButtonDown(object sender, MouseButtonEventArgs e)
        {
            this.isKnobRotating = true;
        }

        void CircularIndicator_MouseMove(object sender, MouseEventArgs e)
        {
            if (this.isKnobRotating == true)
            {
                Point p = new Point(e.GetPosition(this).X, e.GetPosition(this).Y);
                int posVal = ObtenerNuevaPosicion(p);
                _Value = posVal;
            }
        }

The problem is that when I use it from the main window and try to drag the small circle, nothing happens ie the "CnvCirculoP", this does not get the focus, how can I fix, please help me.