When the active tab is tapped again using the UITabBarController

I'm creating it with swift3.

I am switching the screen using the UITabBarController.
FirstViewController and SecondtViewController.
When the FirstViewController screen is active, click the SecondtViewController tab to
I'm switching to the SecondtViewController.
When the FirstViewController screen is active, if you click on the FirstViewController tab, I would like to send a message (it can also be displayed in the console in print).
What should I do?

Resolved