從firarebase接收并將它們寫入回收站視圖的問題

我正在嘗試從 firebase 檢索資料并將它們寫入自定義回收器視圖。我撰寫了代碼，但我不明白為什么沒有正確地從資料庫中獲取資料。

這是主要活動：

private lateinit var myDatabase: FirebaseDatabase
    private lateinit var myReference: DatabaseReference
    private var nameOfTournamentOnDatabase: String = "Tournament"
    private var listOfTournaments: ArrayList<TournamentData> = ArrayList()
    private var adapter: DataListAdapter? = null


    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle? ): View? {
        myDatabase = FirebaseDatabase.getInstance()
        myReference = myDatabase.getReference(nameOfTournamentOnDatabase)

        return inflater.inflate(R.layout.fragment_tournament_list, container, false)
    }

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        var myList: RecyclerView = view.findViewById<RecyclerView>(R.id.myList)
        adapter = DataListAdapter(listOfTournaments, view.context)
        myList.layoutManager = LinearLayoutManager(view.context)
        myList.adapter = adapter
        getDataFromDatabase()
        adapter!!.notifyDataSetChanged()

    }

    private fun getDataFromDatabase(){

       myReference.addListenerForSingleValueEvent(object : ValueEventListener{
           override fun onDataChange(snapshot: DataSnapshot) {
               for(ds in snapshot.children){
                   listOfTournaments.add(TournamentData(ds.child("nameOfTournament").value.toString(),
                       ds.child("nameOfCreator").value.toString(), ds.child("numberOfCompetitors").value.toString(),
                       ds.child("nameOfCompetitors").value.toString()))
               }
           }

           override fun onCancelled(error: DatabaseError) {
               
           }

       })
    }
}

這是自定義配接器類：

class DataListAdapter(private val dataTournamentList: ArrayList<TournamentData>, private val context: Context) : RecyclerView.Adapter<DataListAdapter.ViewHolder> (){

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
        val view = LayoutInflater.from(context).inflate(R.layout.card_layout, parent, false)
        return ViewHolder(view)
    }

    override fun onBindViewHolder(holder: ViewHolder, position: Int) {
        holder.bindItem(dataTournamentList[position])
    }

    override fun getItemCount(): Int {
        return dataTournamentList.size
    }

    inner class ViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {
        fun bindItem(data: TournamentData){
            var tournamentName : TextView = itemView.findViewById(R.id.name_of_tuornament) as TextView
            var nameOfCreator : TextView = itemView.findViewById(R.id.name_of_creator) as TextView
            var numberOfCompetitors : TextView = itemView.findViewById(R.id.number_of_competitor) as TextView

            tournamentName.text = data.nameOfTournament
            nameOfCreator.text = data.nameOfCreator
            numberOfCompetitors.text = data.numberOfCompetitors
        }
    }
}

我不明白為什么資料沒有到達。代碼撰寫正確，沒有錯誤，資料庫設定正確。

uj5u.com熱心網友回復：

adapter.notifyDataSetChanged()在對配接器顯示的資料串列進行任何更改后，您需要呼叫（因此在您的onDataChange.

作為一般規則，我還建議不要onCanceled留空，因為您忽略了可能的錯誤。至少應該是：

public void onCancelled(@NonNull DatabaseError databaseError) { 
    throw databaseError.toException(); 
}

標籤：安卓 科特林 firebase-实时数据库

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