Kotlin Firebase RecyclerView 的问题

Question

我试图在一个片段中创建一个用户 recyclerview，但我无法让它工作。

这个想法是从数据库中获取用户（实际登录的用户除外）并将用户数据添加到列表中。问题是该列表甚至没有出现。

我对 Kotlin 了解不多，我最近才开始使用它，但我正在为此苦苦挣扎。我也不知道问题出在哪里。

如果您需要 XML，请索取

我的片段：

import android.os.Bundle
import android.util.Log
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.Toast
import androidx.appcompat.app.AppCompatActivity
import androidx.fragment.app.Fragment
import androidx.recyclerview.widget.LinearLayoutManager
import androidx.recyclerview.widget.RecyclerView
import com.google.firebase.auth.FirebaseAuth
import com.google.firebase.auth.FirebaseUser
import com.google.firebase.database.*


@Suppress("NULLABILITY_MISMATCH_BASED_ON_JAVA_ANNOTATIONS")
class UsersFragment:Fragment(R.layout.fragment_users) {

    private lateinit var recyclerView: RecyclerView
    private lateinit var adapterUsers: AdapterUsers
    private lateinit var userList: MutableList<ModelUsers>

    override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View {
        super.onCreate(savedInstanceState)
        (activity as AppCompatActivity).supportActionBar?.title = "Users"
    val view: View = inflater.inflate(R.layout.fragment_users, container, false)

    userList = ArrayList()

    getAllUsers()

    adapterUsers = AdapterUsers(context!!, userList)

    recyclerView = view.findViewById(R.id.users_recyclerView)
    recyclerView.setHasFixedSize(true)
    recyclerView.layoutManager = LinearLayoutManager(activity, LinearLayoutManager.VERTICAL, false)
    recyclerView.adapter = adapterUsers

    return view
}

private fun getAllUsers() {
    val fUser: FirebaseUser = FirebaseAuth.getInstance().currentUser
    val ref: DatabaseReference = FirebaseDatabase.getInstance().getReference("Users")

    ref.addValueEventListener(object: ValueEventListener{
        override fun onDataChange(snapshot: DataSnapshot) {
            Log.d("FUNCTION", "ENTER")
            userList.clear()
            for(ds: DataSnapshot in snapshot.children){
                val modelUsers: ModelUsers? = ds.getValue(ModelUsers::class.java)

                if(!modelUsers?.uid.equals(fUser.uid)){
                    userList.add(modelUsers!!)
                    Toast.makeText(activity, "IN", Toast.LENGTH_SHORT).show()
                }
            }
        }

        override fun onCancelled(error: DatabaseError) {
            TODO("Not yet implemented")
        }

    })
}

companion object {
    fun newInstance(): ProfileFragment {
        return ProfileFragment()
    }}}

我的自定义适配器：

import android.content.Context
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.ImageView
import android.widget.TextView
import android.widget.Toast
import androidx.recyclerview.widget.RecyclerView
import com.squareup.picasso.Picasso
import java.lang.Exception

open class AdapterUsers(private var context:Context, private var userList: MutableList<ModelUsers> = mutableListOf<ModelUsers>()): RecyclerView.Adapter<AdapterUsers.UserViewHolder>() {


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

    override fun onBindViewHolder(holder: UserViewHolder, position: Int) {
        val userImage = userList[position].image
        val userName = userList[position].name
        val userEmail = userList[position].email

        holder.mNameTv.text = userName
        holder.mEmailTv.text = userEmail
        try {
            Picasso.get().load(userImage).placeholder(R.drawable.ic_default_image_color).into(holder.mAvatarIv)
        }
        catch (e: Exception){

        }

        holder.itemView.setOnClickListener{
            Toast.makeText(context, userEmail, Toast.LENGTH_SHORT).show()
        }
    }

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

    inner class UserViewHolder(itemView: View): RecyclerView.ViewHolder(itemView){
        val mAvatarIv: ImageView = itemView.findViewById(R.id.avatarIv)
        val mNameTv: TextView = itemView.findViewById(R.id.nameTv)
        val mEmailTv: TextView = itemView.findViewById(R.id.emailTv)
    }
}

用户模型：

data class ModelUsers(
var name: String? = null,
var email: String? = null,
var search: String? = null,
var phone: String? = null,
var image: String? = null,
var cover: String? = null,
var uid: String? = null)

Answer 1

您应该在数据更改后刷新您的回收器视图适配器，尝试像这样更改您的代码：

class UsersFragment:Fragment(R.layout.fragment_users) {

    private lateinit var recyclerView: RecyclerView
    
    private var userList = mutableListOf<ModelUsers>()

    override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View {
        super.onCreate(savedInstanceState)
        (activity as AppCompatActivity).supportActionBar?.title = "Users"
        val view: View = inflater.inflate(R.layout.fragment_users, container, false)

        recyclerView = view.findViewById<RecyclerView>(R.id.users_recyclerView).apply {
            setHasFixedSize(true)
            layoutManager = LinearLayoutManager(requireContext())
            adapter = AdapterUsers(requireContext(), mutableListOf())
        }

        getAllUsers()

        return view
    }

    private fun getAllUsers() {
        val fUser: FirebaseUser = FirebaseAuth.getInstance().currentUser
        val ref: DatabaseReference = FirebaseDatabase.getInstance().getReference("Users")

        ref.addValueEventListener(object: ValueEventListener{
            override fun onDataChange(snapshot: DataSnapshot) {
                Log.d("FUNCTION", "ENTER")
                userList.clear()

                for(ds: DataSnapshot in snapshot.children) {
                    val modelUsers: ModelUsers? = ds.getValue(ModelUsers::class.java)

                    if(!modelUsers?.uid.equals(fUser.uid)){
                        userList.add(modelUsers!!)
                        Toast.makeText(activity, "IN", Toast.LENGTH_SHORT).show()
                    }

                    recyclerView.adapter = AdapterUsers(requireContext(), userList)
                }
            }

            override fun onCancelled(error: DatabaseError) {
                TODO("Not yet implemented")
            }

        })
    }

    companion object {
        fun newInstance(): ProfileFragment {
            return ProfileFragment()
        }
    }
}

Answer 2

问题在于，当您使用适配器时，列表为空，然后可能 0.2 秒后，您已从数据库中获取用户并填充列表，但适配器不知道列表已更改。填充列表后，您可以在适配器上调用 notifyDataSetChanged() 以告知列表已更改。