How do I ensure that the right ViewController is loaded when accepting a file?

How do I ensure that the right ViewController is loaded when accepting a
file?

So I have this setup
Initial VC -> Tab controller -> (three VC's, one of them...) NavController
containing file list -> File editor
At any time, I might get a application:handleOpenUrl message sent to my
app delegate that tells me that the user wants to edit a file, for example
an attachment from an email. Depending on the state of my app, all or some
of these VC's might be loaded. In order to react sensibly to the URL, I
need for the NavController to be loaded at the very least.
I suppose the real objective is to get the app in a state where the
NavController is loaded, and the currently active controller, so I can
send it a message from the AppDelegate to load a given file once it's
processed.
So: What is best practice here?