Kotlin Firestore - 从特定文档中获取字段

Question

I have multiple collections which store various documents, and I'm attempting to reach a specific collection so that I may retrieve fields from a specific document. I am attempting to do this in onStart

John Doe ----> "DocumentId (a23bsz12bvxaQw2)" ----> |name: John Doe, age: 23, occupation: teacher|

I am able to retrieve the specific collection in another method, however that's only because I'm able to pass in the name of the collection as a parameter. The only way for me to reach a specific Collection is by hard-coding the fieldPath .

This is my code thus far:

 override fun onStart() {
    super.onStart()

    val caseManagerNameOnStart = caseManagerName?.text

    val notebookRef = db.collection("$caseManagerNameOnStart")
    notebookRef.addSnapshotListener(this, object : EventListener<QuerySnapshot?> {
        override fun onEvent(querySnap: QuerySnapshot?, ex: FirebaseFirestoreException?) {
            if (ex != null) {
                return
            }
            if (querySnap != null) {
                for (documentSnapshot in querySnap) {
                    val appointment = documentSnapshot.toObject(
                        Appointment::class.java
                    )
                    appointment.setId(documentSnapshot.id)
                    appointment_text_view_date.text =
                        "Date: " + documentSnapshot["dateAppointment"].toString()
                    appointment_text_view_time.text =
                        "Time: " + documentSnapshot["timeAppointment"].toString()
                    appointment_text_view_case_manager.text =
                        "Case Manager: " + documentSnapshot["caseManagerName"].toString()
                    appointment_text_view_client_name.text =
                        "Client: " + documentSnapshot["userName"].toString()
                    appointment_text_view_format.text =
                        "Format: " + documentSnapshot["formatAppointment"].toString()
                }
            }
        }
    })
}

val caseManagerNameOnStart = caseManagerName?.text seems to be empty, and the app crashes when I call the activity in question. caseManagerName should hold the name which can be used in for fieldPath , however there is a case where there might not be a collection to retrieve, and thus nothing should be set to the TextViews.

My expected output is this:

1. Get specified collection
2. Retrieve fields from document
3. Display these fields in given TextViews
4. If no collection is available, prevent onStart from crashing app.

Here is an image of my data in Firestore. Firestore Data

I would highly appreciate any input. Thank you for your time.

Answer 1

however that's only because I'm able to pass in the name of the collection as a parameter.

It is mandatory to know the name of the collection, in order to access the properties of the documents.

val caseManagerNameOnStart = caseManagerName?.text seems to be empty, and the app crashes

It is empty, the reason why you have that crash.

caseManagerName should hold the name which can be used in for fieldPath

Or you can save the name of the collection in another type of object, for example, in SharedPreferences.

however there is a case where there might not be a collection to retrieve, and thus nothing should be set to the TextViews.

This is how you can check a collection for existence, before setting something in the reference.

• check collection existence - Firestore