在Swift3中使用removeObserver(withHandle，不会在viewDidDisappear上删除观察者varquery=FIRDatabaseQuery()varpostRef:FIRDatabaseReference!varpostRefHandle:FIRDatabaseHandle?overridefuncviewDidLoad(){super.viewDidLoad()postRef=baseRef.child("Posts")}overridefuncviewDidDisappear(_animated:Bool){super.viewDidDisappe