private void c_MouseDown(object sender, System.Windows.Input.MouseEventArgs mevent)
        {
            IsDragMode = true;
        }

        private void c_MouseUp(object sender, System.Windows.Input.MouseEventArgs mevent)
        {
            IsDragMode = false;
        }

        private void c_MouseMove(object sender, System.Windows.Input.MouseEventArgs mevent)
        {
            if (IsDragMode)
            {
                System.Windows.Controls.Button c = sender as System.Windows.Controls.Button;

                TranslateTransform transform = new TranslateTransform();
                transform.X = Mouse.GetPosition(MainGrid).X;
                transform.Y = Mouse.GetPosition(MainGrid).Y;
                c.RenderTransform = transform;
            }
        }

            System.Windows.Controls.Button b = new System.Windows.Controls.Button();
            b.Width = 800;
            b.Height = 500;
            b.Margin = new Thickness(20, 20, 20, 20);
            MainGrid.Children.Add(b);
            b.PreviewMouseDown += c_MouseDown;
            b.PreviewMouseMove += c_MouseMove;
            b.PreviewMouseUp += c_MouseUp;

                TranslateTransform transform = new TranslateTransform();
                transform.X = Mouse.GetPosition(MainGrid).X;
                transform.Y = Mouse.GetPosition(MainGrid).Y;
                TranslateTransform transform2 = new TranslateTransform();
                transform2.X = Mouse.GetPosition(c as UIElement).X;
                transform2.Y = Mouse.GetPosition(c as UIElement).Y;
                transform.X += transform2.X;
                transform.Y += transform2.Y;
                c.RenderTransform = transform;