如何使用Kotlin中的await（）使用Firestore databse：addSnapshotListener？

Question

 suspend fun fetchHubList(): ArrayList<HubModel>? = try {
        val hubList = ArrayList<HubModel>()

        hubsListCollection.get().await().map { document ->

            if (document != null) {

                Log.d(TAG, "Data fetch successful!")
                Log.d(TAG, "the document id is ${document.id}")

                val temp = HubModel(document.get("hubName").toString(),
                                    document.id.toString(),
                        document.get("isAdmin") as Boolean)
                hubList.add(temp)

                     //   hubList.add(document.toObject(HubModel::class.java))

            } else {
                Log.d(TAG, "No such document")
            }

        }

suspend fun fetchHubList(): ArrayList<HubModel>? = try {
        val hubList = ArrayList<HubModel>()

        hubsListCollection.addSnapshotListener().await().map { document ->

            if (document != null) {

                Log.d(TAG, "Data fetch successful!")
                Log.d(TAG, "the document id is ${document.id}")

                val temp = HubModel(document.get("hubName").toString(),
                                    document.id.toString(),
                        document.get("isAdmin") as Boolean)
                hubList.add(temp)

                     //   hubList.add(document.toObject(HubModel::class.java))

            } else {
                Log.d(TAG, "No such document")
            }

        }

我在ViewModel类中使用这个函数来创建LiveData包装的ArrayList：

val hubList =  MutableLiveData<ArrayList<HubModel>>()
    private val hubListDao = HubListDao()
    init {
        viewModelScope.launch {

            hubList.value = hubListDao.fetchHubList()
        }
    }

提前感谢！

Answer 1

您不需要AddSnapshotListener，只需使用get:

hubsListCollection.get().await()

为了观察集合中的更改，可以扩展LiveData:

class CafeLiveData(
    private val documentReference: DocumentReference
) : LiveData<Cafe>(), EventListener<DocumentSnapshot> {

    private var snapshotListener: ListenerRegistration? = null

    override fun onActive() {
        super.onActive()
        snapshotListener = documentReference.addSnapshotListener(this)
    }

    override fun onInactive() {
        super.onInactive()
        snapshotListener?.remove()
    }

    override fun onEvent(result: DocumentSnapshot?, error: FirebaseFirestoreException?) {
        val item = result?.let { document ->
            document.toObject(Cafe::class.java)
        }
        value = item!!
    }
}

并从视图模型中公开它：

fun getCafe(id: String): LiveData<Cafe> {
    val query = Firebase.firestore.document("cafe/$id")
    return CafeLiveData(query)
}