Android Kotlin Wait For Firebsae Realtime Database For-Loop Completion

Question

I am having some problems with Firebase and Kotlin for loop.

See the scenario below.

I have a list of classes of a school (have already in a variable from another source)
There several sections for each of the classes in the Firebase Realtime Database
I want to get all the sections from the database for the class list
Finally I want to show the section list as a dialog

Here is a sample code

private val firebaseDB = Firebase.database.reference
private val clazzList: ArrayList<Clazz> = ArrayList()

private fun getSections() {
    val sectionList: ArrayList<Section> = ArrayList()
    for (clazz in clazzList) {
        firebaseDB.child("schools").child("sections")
            .orderByChild("classNodeKey")
            .equalTo(clazz.nodeKey)
            .addListenerForSingleValueEvent(object : ValueEventListener {
                override fun onCancelled(p0: DatabaseError) {}

                override fun onDataChange(p0: DataSnapshot) {
                    if (p0.exists()) {
                        val hashDataArray: ArrayList<HashMap<*, *>> = ArrayList()
                        for (datasnapshot in p0.children) {
                            hashDataArray.add(datasnapshot.value as java.util.HashMap<*, *>)
                        }
                        for (hashData in hashDataArray) {
                            val sectionObject = Gson().fromJson(Gson().toJsonTree(hashData), Section::class.java) as Section
                            sectionList.add(sectionObject)
                        }
                    }
                }
            })
    }
    showSections(sectionList) // Show the section list in a dialog. It is being called before the completion of for-loop above.
}

private fun showSections(sectionList: ArrayList<Section>) {
    MaterialDialog(this).show {
        title(text = "Sections")
        listItemsSingleChoice(items = sectionList)
        positiveButton(text = "OK")
    }
}

Here is the data model class Clazz.kt

data class Clazz (val nodeKey: String, val name: String)

Here everything is working fine except one thing and that is The method showSections(sectionList: ArrayList) is being executed before the completion of for-loop and the dialog is showing an empty list

But I want to first complete the for-loop and then want to show the dialog. How can I achieve this?

See here: https://stackoverflow.com/questions/60520000/ – MMG Mar 30 '20 at 07:45 — MMG, Mar 30 '20 at 07:45

score 0 · Answer 1 · answered Mar 30 '20 at 09:18

Take showSections(sectionList) into if (p0.exists()):

 private val firebaseDB = Firebase.database.reference
    private val clazzList: ArrayList<Clazz> = ArrayList()

    private fun getSections() {
        val sectionList: ArrayList<Section> = ArrayList()
        for (clazz in clazzList) {
            firebaseDB.child("schools").child("sections")
                .orderByChild("classNodeKey")
                .equalTo(clazz.nodeKey)
                .addListenerForSingleValueEvent(object : ValueEventListener {
                    override fun onCancelled(p0: DatabaseError) {}

                    override fun onDataChange(p0: DataSnapshot) {
                        if (p0.exists()) {
                            val hashDataArray: ArrayList<HashMap<*, *>> = ArrayList()
                            for (datasnapshot in p0.children) {
                                hashDataArray.add(datasnapshot.value as java.util.HashMap<*, *>)
                            }
                            for (hashData in hashDataArray) {
                                val sectionObject = Gson().fromJson(Gson().toJsonTree(hashData), Section::class.java) as Section
                                sectionList.add(sectionObject)
                            }
    showSections(sectionList) // Show the section list in a dialog. It is being called before the completion of for-loop above.
                        }
                    }
                })
        }
    }

    private fun showSections(sectionList: ArrayList<Section>) {
        MaterialDialog(this).show {
            title(text = "Sections")
            listItemsSingleChoice(items = sectionList)
            positiveButton(text = "OK")
        }
    }

Yes I have tried that. But same things happen. It shows the dialog before getting all the sections. — Bahar, Apr 01 '20 at 13:56

Android Kotlin Wait For Firebsae Realtime Database For-Loop Completion

1 Answers1