我无法在Firestore addSnapshotListener中调用“ snapshot.documentChanges”

Question

我无法在foo中致电snapshot.documentChanges

它说addSnapshotListener

Xcode 10.2，Swift 5，Firestore 5.10.0以及有关其他库的更多信息都在下面

Value of type 'DocumentSnapshot' has no member 'documentChanges'

Podfile

    fileprivate func setupSnapshotListener() {
        let coupleId = "B9C950640E1B3740E98ACB93E669C65766F6670DD1609BA91FF41052BA48C6F3"

        let ref = Firestore.firestore().collection("couples").document(coupleId).collection("vibrations").document("vibrationStatus")

        ref.addSnapshotListener { (querySnapshot, err) in
            guard let snapshot = querySnapshot else {
                print(err)
                return
            }

            snapshot.documentChanges.forEach { diff in
                if (diff.type == .added) {
                    print("New city: \(diff.document.data())")
                }
                if (diff.type == .modified) {
                    print("Modified city: \(diff.document.data())")
                }
                if (diff.type == .removed) {
                    print("Removed city: \(diff.document.data())")
                }
            }
        }
    }

我希望像Google Firebase Document所说的那样使用 pod 'Firebase/Firestore’,’~>5.10.0’ pod 'Firebase/Auth’,’~>5.10.0’ pod 'Firebase/Storage’,’~>5.10.0’ pod 'Firebase/Core’ pod 'GoogleAppMeasurement', '~> 5.2.0' pod 'JGProgressHUD','~>2.0.3' pod 'GoogleUtilities' ，但是我不能打电话给addListener！