Hello Bartosz,

Thank you for your feedback.

Indeed, exposing some API to be able to customize this behavior seems like a reasonable request. That's why I'm converting this bug report to a feature request and we will think of possible ways to allow for such customization in the future.

For the time being, I can suggest handling the SelectionChanged event (for example) in a similar manner:

        private void diagram_SelectionChanged(object sender, SelectionChangedEventArgs e)
        {
            if (e.AddedItems != null && e.AddedItems.Count > 0)
            {
                var containerItem = e.AddedItems[0] as ContainerNodeViewModelBase<object>;
                var container = this.diagram.ContainerGenerator.ContainerFromItem(containerItem) as RadDiagramContainerShape;
                if (container != null)
                {
                    foreach (var shape in this.diagram.Shapes)
                    {
                        if (container.ContentBounds.Contains(shape.Bounds))
                        {
                            var shapeItem = this.diagram.ContainerGenerator.ItemFromContainer(shape) as NodeViewModelBase;
                            if (shape.ParentContainer == null && shapeItem != containerItem && !containerItem.InternalItems.Contains(shapeItem))
                            {
                                containerItem.AddItem(shapeItem);
                            }
                        }
                    }
                }
            }
        }

This logic will iterate all the shapes and determine if any of them are placed on top of the selected container - if that is the case, they will be added to it and once you start the drag operation, these shapes will be dragged as well.

You can extract this logic in a separate method and call it if this check needs to be performed at a different moment - when programmatically moving a shape, for example.

Please let me know if such an approach would work for you for the time being.

Regards,
Dilyan Traykov
Progress Telerik

Hello Bartosz,

This is the default behavior of the RadDiagram element because all of its items are rendered as a flat collection on a single surface and the shapes are only logical children of the containers. This could be observed by using a spying utility, such as Snoop, which would allow you to inspect the visual tree of the RadDiagram control. Moreover, when the container and, for example, a RadDiagramShape are selected, they are automatically placed in a selection adorner, which allows the user to drag them around the RadDiagram control's surface.

With that said, I hope the provided information is of help to you.

Regards,
Stenly
Progress Telerik