[Firebase] Cloud Firestore 데이터 읽기

1. 어댑터

class ReadRecyclerViewAdapter(initList:ArrayList<UserDTO>) : RecyclerView.Adapter<RecyclerView.ViewHolder>(){

    var list: ArrayList<UserDTO>? = initList

    override fun onCreateViewHolder(parent: ViewGroup?, viewType: Int): RecyclerView.ViewHolder {
        var view = LayoutInflater.from(parent!!.context).inflate(R.layout.item_recyclerview, parent, false)
        return CustomViewHolder(view)
    }

    class CustomViewHolder(view: View?) : RecyclerView.ViewHolder(view) {
        var textview_name = view!!.findViewById<TextView>(R.id.textView_name)
        var textview_age = view!!.findViewById<TextView>(R.id.textView_age)
        var textview_city = view!!.findViewById<TextView>(R.id.textView_city)
    }

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

    override fun onBindViewHolder(holder: RecyclerView.ViewHolder?, position: Int) {
        var customViewHolder = holder as CustomViewHolder
        customViewHolder.textview_name.text = list!!.get(position).name
        customViewHolder.textview_age.text = list!!.get(position).age.toString()
        customViewHolder.textview_city.text = list!!.get(position).city
    }
}

2. Get방식

-한번 받아온다.

//Get
FirebaseFirestore.getInstance().collection("users").get().addOnSuccessListener { querySnapshot ->
    for(item in querySnapshot.documents){
        var userDTO = item.toObject(UserDTO::class.java)
        arrayList.add(userDTO!!)
    }
    recyclerview_read_database.adapter = ReadRecyclerViewAdapter(arrayList)
    recyclerview_read_database.layoutManager = LinearLayoutManager(this)
}

3. Snapshot방식

-수정내역을 즉시 반영

recyclerview_read_database_realtime.adapter = ReadRecyclerViewAdapter(realTimeArrayList)
recyclerview_read_database_realtime.layoutManager = LinearLayoutManager(this)
FirebaseFirestore.getInstance().collection("users").addSnapshotListener { querySnapshot, firebaseFirestoreException ->

    realTimeArrayList.clear() //없에버리고
    for(item in querySnapshot!!.documents){
        var userDTO = item.toObject(UserDTO::class.java)
        realTimeArrayList.add(userDTO!!)
    }
    recyclerview_read_database.adapter.notifyDataSetChanged()
}

3. Snapshot방식 개선

-기존은 새로 바뀔때마다 전체를 새로고침하지만, 이 코드는 바뀐 부분만 새로고침한다. 

var realTimeArrayList = arrayListOf<UserDTO>()
var realTimeKeyArrayList = arrayListOf<String>() //키값을 따로

    recyclerview_read_database_realtime.adapter = ReadRecyclerViewAdapter(realTimeArrayList)
    recyclerview_read_database_realtime.layoutManager = LinearLayoutManager(this)
    FirebaseFirestore.getInstance().collection("users").addSnapshotListener { querySnapshot, firebaseFirestoreException ->

        for(item in querySnapshot!!.documentChanges){
            when(item.type){
                DocumentChange.Type.ADDED -> {
                    realTimeArrayList.add(item.document.toObject(UserDTO::class.java))
                    realTimeKeyArrayList.add(item.document.id)
                }
                DocumentChange.Type.MODIFIED -> modifyItem(item.document.id, item.document.toObject(UserDTO::class.java))
                DocumentChange.Type.REMOVED -> deleteItem(item.document.id)
            }
        }
        recyclerview_read_database_realtime.adapter.notifyDataSetChanged()

    }
}

fun modifyItem(deleteKey: String, userDTO: UserDTO){
    for( (position, item) in realTimeArrayList.withIndex() ){

    }
}

fun deleteItem(deleteKey: String){
    for( (position, item) in realTimeKeyArrayList.withIndex() ){
        if(deleteKey == item){
            realTimeArrayList.removeAt(position)
        }
    }
}

4. 전체코드

package com.example.lipnus.firebaseauth

import android.support.v7.app.AppCompatActivity
import android.os.Bundle
import android.support.v7.widget.LinearLayoutManager
import android.support.v7.widget.RecyclerView
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.TextView
import com.google.firebase.firestore.DocumentChange
import com.google.firebase.firestore.FirebaseFirestore
import kotlinx.android.synthetic.main.activity_read_database.*

class ReadDatabaseActivity : AppCompatActivity() {

    var realTimeArrayList = arrayListOf<UserDTO>()
    var realTimeKeyArrayList = arrayListOf<String>() //키값을 따로

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_read_database)

        var userDTO = UserDTO("선필", 25, "서울")
        var arrayList = arrayListOf<UserDTO>()
//        arrayList.add(userDTO)
//        arrayList.add(userDTO)




        //Get
        FirebaseFirestore.getInstance().collection("users").get().addOnSuccessListener { querySnapshot ->
            for(item in querySnapshot.documents){
                var userDTO = item.toObject(UserDTO::class.java)
                arrayList.add(userDTO!!)
            }
            recyclerview_read_database.adapter = ReadRecyclerViewAdapter(arrayList)
            recyclerview_read_database.layoutManager = LinearLayoutManager(this)
        }

        //SnapShot
//        recyclerview_read_database_realtime.adapter = ReadRecyclerViewAdapter(realTimeArrayList)
//        recyclerview_read_database_realtime.layoutManager = LinearLayoutManager(this)
//        FirebaseFirestore.getInstance().collection("users").addSnapshotListener { querySnapshot, firebaseFirestoreException ->
//
//            realTimeArrayList.clear() //없에버리고
//            for(item in querySnapshot!!.documents){
//                var userDTO = item.toObject(UserDTO::class.java)
//                realTimeArrayList.add(userDTO!!)
//            }
//            recyclerview_read_database.adapter.notifyDataSetChanged()
//        }

        recyclerview_read_database_realtime.adapter = ReadRecyclerViewAdapter(realTimeArrayList)
        recyclerview_read_database_realtime.layoutManager = LinearLayoutManager(this)
        FirebaseFirestore.getInstance().collection("users").addSnapshotListener { querySnapshot, firebaseFirestoreException ->

            for(item in querySnapshot!!.documentChanges){
                when(item.type){
                    DocumentChange.Type.ADDED -> {
                        realTimeArrayList.add(item.document.toObject(UserDTO::class.java))
                        realTimeKeyArrayList.add(item.document.id)
                    }
                    DocumentChange.Type.MODIFIED -> modifyItem(item.document.id, item.document.toObject(UserDTO::class.java))
                    DocumentChange.Type.REMOVED -> deleteItem(item.document.id)
                }
            }
            recyclerview_read_database_realtime.adapter.notifyDataSetChanged()

        }
    }

    fun modifyItem(deleteKey: String, userDTO: UserDTO){
        for( (position, item) in realTimeArrayList.withIndex() ){

        }
    }

    fun deleteItem(deleteKey: String){
        for( (position, item) in realTimeKeyArrayList.withIndex() ){
            if(deleteKey == item){
                realTimeArrayList.removeAt(position)
            }
        }
    }



    class ReadRecyclerViewAdapter(initList:ArrayList<UserDTO>) : RecyclerView.Adapter<RecyclerView.ViewHolder>(){

        var list: ArrayList<UserDTO>? = initList

        override fun onCreateViewHolder(parent: ViewGroup?, viewType: Int): RecyclerView.ViewHolder {
            var view = LayoutInflater.from(parent!!.context).inflate(R.layout.item_recyclerview, parent, false)
            return CustomViewHolder(view)
        }

        class CustomViewHolder(view: View?) : RecyclerView.ViewHolder(view) {
            var textview_name = view!!.findViewById<TextView>(R.id.textView_name)
            var textview_age = view!!.findViewById<TextView>(R.id.textView_age)
            var textview_city = view!!.findViewById<TextView>(R.id.textView_city)
        }

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

        override fun onBindViewHolder(holder: RecyclerView.ViewHolder?, position: Int) {
            var customViewHolder = holder as CustomViewHolder
            customViewHolder.textview_name.text = list!!.get(position).name
            customViewHolder.textview_age.text = list!!.get(position).age.toString()
            customViewHolder.textview_city.text = list!!.get(position).city
        }
    }
}

4. Firebase console

-콘솔에서는 다음과 같이 표시된다