drawing line wpf vb

What did I do wrong? It seems like it works to me.

Imports System.Math
Class LineLengthWindow
    Dim xDistance1 As Double
    Dim yDistance1 As Double
    Dim xDistance2 As Double
    Dim yDistance2 As Double
    Dim first_test As Boolean = False
    Dim myLine As New Line()
    Public Sub length_line(ByVal x, ByVal y)
        Dim legnth As Double = Math.Sqrt(x ^ 2 + y ^ 2)
        lengthOutputLabel.Content = legnth.ToString
    End Sub
    Private Sub lineCanvas_MouseLeftButtonDown( _
 ByVal sender As Object, _
 ByVal e As System.Windows.Input.MouseButtonEventArgs)

        Dim mousePosition As Point = e.GetPosition(lineCanvas)
        'Grab mouse XY position on left mouse button down click
        If first_test = False Then
            xDistance1 = mousePosition.X
            yDistance1 = mousePosition.Y
            first_test = True
        ElseIf first_test = True Then
            xDistance2 = mousePosition.X
            yDistance2 = mousePosition.Y
        End If

    End Sub

    Private Sub lineCanvas_MouseLeftButtonUp( _
ByVal sender As Object, _
ByVal e As System.Windows.Input.MouseButtonEventArgs)
        Dim mousePosition As Point = e.GetPosition(lineCanvas)

        If first_test = True Then   'to make sure the user clicked twice and to draw on the second mouse up

            'draw the line code starts here
            myLine.Stroke = Brushes.Black
            myLine.X1 = xDistance1
            myLine.X2 = mousePosition.X
            myLine.Y1 = yDistance1
            myLine.Y2 = mousePosition.Y
            myLine.HorizontalAlignment = HorizontalAlignment.Left
            myLine.VerticalAlignment = VerticalAlignment.Center
            myLine.StrokeThickness = 2
            lineCanvas.Children.Add(myLine)
            'ends here

            'pass the coordinates to the method to calculate the line length
            length_line((xDistance1 + xDistance2), (yDistance1 + yDistance2))
        End If
    End Sub
End Class

Imports System.Math
Class LineLengthWindow
    Dim xDistance1 As Double
    Dim yDistance1 As Double
    Dim xDistance2 As Double
    Dim yDistance2 As Double
    Dim first_test As Boolean = False
    Dim myLine As New Line()
    Public Sub length_line(ByVal x, ByVal y)
        Dim legnth As Double = Math.Sqrt(x ^ 2 + y ^ 2)
        lengthOutputLabel.Content = legnth.ToString
    End Sub
    Private Sub lineCanvas_MouseLeftButtonDown( _
 ByVal sender As Object, _
 ByVal e As System.Windows.Input.MouseButtonEventArgs)

        Dim mousePosition As Point = e.GetPosition(lineCanvas)
        'Grab mouse XY position on left mouse button down click
        If first_test = False Then
            xDistance1 = mousePosition.X
            yDistance1 = mousePosition.Y
            first_test = True
        ElseIf first_test = True Then
            xDistance2 = mousePosition.X
            yDistance2 = mousePosition.Y
        End If

    End Sub

    Private Sub lineCanvas_MouseLeftButtonUp( _
ByVal sender As Object, _
ByVal e As System.Windows.Input.MouseButtonEventArgs)
        Dim mousePosition As Point = e.GetPosition(lineCanvas)

        If first_test = True Then   'to make sure the user clicked twice and to draw on the second mouse up

            'draw the line code starts here
            myLine.Stroke = Brushes.Black
            myLine.X1 = xDistance1
            myLine.X2 = mousePosition.X
            myLine.Y1 = yDistance1
            myLine.Y2 = mousePosition.Y
            myLine.HorizontalAlignment = HorizontalAlignment.Left
            myLine.VerticalAlignment = VerticalAlignment.Center
            myLine.StrokeThickness = 2
            lineCanvas.Children.Add(myLine)
            'ends here

            'pass the coordinates to the method to calculate the line length
            length_line((xDistance1 + xDistance2), (yDistance1 + yDistance2))
        End If
    End Sub
End Class