How to realize a movable controller in iPadOS, like mail APP in iPad

问题

Mail App in iPad, when we create a new mail, the controller will be presented. But in iPadOS system, this controller can be moved, and if move it to the left side or right side, it can become a multiple window. How Apple to realize this feature?

I try a lot new API about UIViewController but it does not work.

来源：https://stackoverflow.com/questions/57238686/how-to-realize-a-movable-controller-in-ipados-like-mail-app-in-ipad