Basic drag & drop

dad.cs

// ------------------- Drag side -----------------------
// -----------------------------------------------------

Point StartPosition;

 private void PLC_PreviewMouseMove(object sender, MouseEventArgs e)
        {
            if (e.LeftButton == MouseButtonState.Pressed)
            {
                Point mousePos = e.GetPosition(null);
                Vector diff = StartPosition - mousePos;

                if (Math.Abs(diff.X) > SystemParameters.MinimumHorizontalDragDistance ||
                    Math.Abs(diff.Y) > SystemParameters.MinimumVerticalDragDistance)
                {
                    PlcButton butt = (PlcButton)sender;
                    DataObject dragData = new DataObject("DragPlcFormat", butt.s7plc);
                    DragDrop.DoDragDrop(this, dragData, DragDropEffects.Move);
                    Refresh();
                }

            }
        }

        private void PLC_PreviewMouseLeftButtonDown(object sender, MouseButtonEventArgs e)
        {
            StartPosition = e.GetPosition(null);
        }
        
// ------------------- Drop side -----------------------
// -------- Must allow drop inside control XAML --------
 
 private void UserControl_DragEnter(object sender, DragEventArgs e)
        {
            if (!e.Data.GetDataPresent("DragPlcFormat"))
            {
                //
            }
        }

        private void UserControl_Drop(object sender, DragEventArgs e)
        {
            if (e.Data.GetDataPresent("DragPlcFormat"))
            {
                S7PLC draged = (S7PLC)e.Data.GetData("DragPlcFormat");
                draged.UpdateGroup(ID_GROUP);
                Refresh();
            }
        }