How do I capture the event when guest join the waiting room

I am using custom UI and enable waiting room feature. How can I capture the joining event when guest join the waiting room? 

When the host enters the meeting, it can trigger onWaitingRoomStatusChange, but no event trigger when other guest join in.

Here is my code

extension ClassRoomViewController: MobileRTCMeetingServiceDelegate, MobileRTCVideoServiceDelegate, MobileRTCAudioServiceDelegate, MobileRTCWaitingRoomServiceDelegate {

func onWaitingRoomStatusChange(_ needWaiting: Bool) {
print("trigger onWaitingRoomStatusChange2")
if needWaiting {
print("User joined waiting room.")
// showAlert(with: "User now in waiting room.", and: "User needs to be admitted by host or leave.", action: UIAlertAction(title: "Leave", style: .default, handler: { _ in
// MobileRTC.shared().getMeetingService()?.leaveMeeting(with: .leave)
// }))
} else {
print("User is entering meeting.")
delegate?.userWasAdmittedFromTheWaitingRoom()
}
}

func onWaitingRoomUserJoin(_ userId: UInt) {
print("trigger onWaitingRoomUserJoin user join \(userId)")
}

func onWaitingRoomUserLeft(_ userId: UInt) {
print("trigger onWaitingRoomUserLeft user left \(userId)")
}

}