System.Windows.Controls.ComboBox.UpdatePopupSizeAndPosition C# (CSharp) Method

		void UpdatePopupSizeAndPosition (object sender, EventArgs args)
		{
			if (_popup == null)
				return;

			FrameworkElement child = _popup.RealChild as FrameworkElement;
			if (child == null)
				return;

			child.MinWidth = ActualWidth;
			
			var root = Application.Current.Host.Content;
			if (root == null)
				return;

			GeneralTransform xform;

			try {
				xform = TransformToVisual (null);
			}
			catch (ArgumentException) {
				// exception is raised if the combobox is no longer in the visual tree
				// LayoutUpdated -= UpdatePopupSizeAndPosition;
				return;
			}
			
			Point bottom_right = new Point (child.ActualWidth, ActualHeight + child.ActualHeight);
			bottom_right = xform.Transform (bottom_right);

			if (bottom_right.X > root.ActualWidth) {
				_popup.HorizontalOffset = root.ActualWidth - bottom_right.X;
			} else {
				_popup.HorizontalOffset = 0;
			}
			if (bottom_right.Y > root.ActualHeight) {
				_popup.VerticalOffset = -child.ActualHeight;
			} else {
				_popup.VerticalOffset = RenderSize.Height;
			}
			
			// Silverlight does not resize its dropdown properly when the available height is altered.
			// This means that if you open a dropdown while your browser window is small, you end up
			// with a dropdown that is far too small forever. Instead of this we will resize the dropdown
			// to a more usable height.
			UpdatePopupMaxHeight (MaxDropDownHeight);
		}