How to create a pop-up menu with all DockLayoutManager's panels

This example demonstrates how to create a pop-up menu with all DockLayoutManager's panels, which show the current active state of each panel.
For this, we create a BarManager with a BarSubItem. After that, we subscribe to the BarSubItem's Popup event. When Popup is raised, we get a list of all DockLayoutManager's panels. We iterate through this list and add this BarCheckItem to the BarSubItem with a respective panel as a tag. We check the DockLayoutSource's ActiveLayoutItem. If the ActiveLayoutItem equals a panel from the list, we set the BarCheckItem's IsChecked property to True. Then, we subscribe to the BarCheckItem's CheckedChanged event. When CheckedChanged is raised, we get a panel from a current BarCheckItem's tag and activate this panel.