I use a Syncfusion-DockingManager to display a UserControl as content of a ContentControl. A property UserControl (also as content of a ContentControl) can be opened which displays data related to the main user control. On closing the main content control I want to close the respective property content control too.
With Window objects there is the Owner property to set up relations. I looked for a similar property/functionality in ContentControl and didn't find any. It is not possible to change the parent of a ContentControl. I also tried to link Childrenof the DockingManager in syntax like DockingManager.Children[0].IsRelatedTo(DockingManager.Children[1]).
I could store the indices of the "children" of the main content control and close them by hand on WindowClosing. However there should be a be a cleaner way.
You can assign the dependent user control as the tag of the MainUserControl. This tag can be utilized to access the dependent user control and close it when the MainUserControl is being closed.