title: How to detect Persistent BottomSheet Dismissal
body: <p>I am trying to detect the closure of a Persistent BottomSheet. I open the sheet using the scaffoldKey.currentState.showBottomSheet. The showBottomSheet only returns a PersistentBottomSheetController which you can't add a listener to. I am not sure how else to detect the close of the sheet. I need to know when the sheet is closed to change the state of a button.</p>