Ho lavorato un po sul drag and drop sempre per il mio lavoretto sul tris.

Lascio qui il codice, magari potesse servire a qualcuno

Class Window1

Private startPoint As Point = Nothing
Private selectedElementOrigins As Point = Nothing
Private isDragging As Boolean
Private selectedElement As UIElement

Private Sub Window1_Loaded(ByVal sender As System.Object, ByVal e As System.Windows.RoutedEventArgs) Handles MyBase.Loaded

End Sub

Protected Overrides Sub OnPreviewMouseLeftButtonDown(ByVal e As System.Windows.Input.MouseButtonEventArgs)
MyBase.OnPreviewMouseLeftButtonDown(e)

'Se l'oggetto che ha scatenato l'evento non è la "window" allora vai avanti
If (Not (e.Source Is Me)) Then

'Se la variabile è false
If Not (isDragging) Then
'Dammi le coordinate di partenza del click del mouse
startPoint = e.GetPosition(Me)
'Identifica la sorgente che ha scatenato gli eventi
selectedElement = e.Source

Me.CaptureMouse()
isDragging = True
selectedElementOrigins = New Point(Canvas.GetLeft(selectedElement), Canvas.GetTop(selectedElement))
End If
e.Handled = True 'impostando a true si arresta il routing dell'evento
End If
End Sub


Protected Overrides Sub OnPreviewMouseLeftButtonUp(ByVal e As System.Windows.Input.MouseButtonEventArgs)
MyBase.OnPreviewMouseLeftButtonUp(e)

If (Me.IsMouseCaptured) Then
isDragging = False
Me.ReleaseMouseCapture()
e.Handled = True
End If
End Sub

Protected Overrides Sub OnPreviewMouseMove(ByVal e As System.Windows.Input.MouseEventArgs)
MyBase.OnPreviewMouseMove(e)

If (Me.IsMouseCaptured) Then
If (isDragging) Then
Dim CurrentPosition As New Point(e.GetPosition(Me).X, e.GetPosition(Me).Y)
Dim ElementLeft As Double = (CurrentPosition.X - startPoint.X) + selectedElementOrigins.X
Dim ElementTop As Double = (CurrentPosition.Y - startPoint.Y) + selectedElementOrigins.Y
Canvas.SetLeft(selectedElement, ElementLeft)
Canvas.SetTop(selectedElement, ElementTop)
End If
End If
End Sub




End Class






Funziona con un canvas, e un qualsiasi elemento UiElement