RecyclerView 上未解析的参考

Question

I'm able to retrieve the data from Firebase but when I try to load it into the groupie adapter, the recyclerview activity is not loading, and shows the following error "Unresolved reference: None of the following candidates are applicable because of receiver type mismatch....", I am I missing dependency??

This is my activity code, under to the fetchUser method is where I get the error:

import android.os.Bundle
import android.util.Log
import androidx.appcompat.app.AppCompatActivity
import com.google.firebase.database.DataSnapshot
import com.google.firebase.database.DatabaseError
import com.google.firebase.database.FirebaseDatabase
import com.google.firebase.database.ValueEventListener
import com.xwray.groupie.GroupAdapter
import com.xwray.groupie.GroupieViewHolder
import com.xwray.groupie.Item
import kotlinx.android.synthetic.main.activity_new_message.*

class NewMessageActivity : AppCompatActivity() {

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


        // Activity screen title
        supportActionBar?.title = "Select User"

        val adapter = GroupAdapter<GroupieViewHolder>()


        adapter.add(UserItem())
        adapter.add(UserItem())
        adapter.add(UserItem())

        recycler_view_new_message.adapter = adapter

        fetchUsers()

    }
}

private fun fetchUsers() {
    val ref = FirebaseDatabase.getInstance().getReference("/users")
    ref.addListenerForSingleValueEvent(object: ValueEventListener {

        override fun onDataChange(p0: DataSnapshot) {
            val adapter = GroupAdapter<GroupieViewHolder>()


            p0.children.forEach {
                Log.d("NewMessage", it.toString())
                val user = it.getValue(User::class.java)
                adapter.add(UserItem())
            }
            recycler_view_new_message.adapter = adapter /// THIS IS WHERE I GET THE UNRESOLVED REFERENCE ERROR
        }

        override fun onCancelled(p0: DatabaseError) {

        }
    })


}

class UserItem: Item<GroupieViewHolder>() {
    override fun bind(viewHolder: GroupieViewHolder, position: Int) {
    }

    override fun getLayout(): Int {
        return R.layout.user_row_new_message
    }

}

This is the gradle dependencies:

    implementation fileTree(dir: 'libs', include: ['*.jar'])
    implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version"
    implementation 'androidx.appcompat:appcompat:1.0.2'
    implementation 'androidx.core:core-ktx:1.0.2'
    implementation 'androidx.constraintlayout:constraintlayout:1.1.3'
    testImplementation 'junit:junit:4.12'
    androidTestImplementation 'androidx.test.ext:junit:1.1.0'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.1.1'

    implementation 'com.google.firebase:firebase-analytics:17.2.0'
    implementation 'com.google.firebase:firebase-auth:19.2.0'

    implementation 'com.google.firebase:firebase-storage:19.1.0'
    implementation 'com.google.firebase:firebase-database:19.1.0'
    implementation 'de.hdodenhof:circleimageview:3.0.1'
    implementation 'androidx.recyclerview:recyclerview:1.1.0'
    implementation "com.xwray:groupie:2.7.0"

    implementation 'com.squareup.picasso:picasso:2.71828'


}

apply plugin: 'com.google.gms.google-services'

and this is my recyclerView XML config:

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".NewMessageActivity">

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/recycler_view_new_message"
        android:layout_width="0dp"
        android:layout_height="0dp"
        app:layoutManager="androidx.recyclerview.widget.LinearLayoutManager"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />


</androidx.constraintlayout.widget.ConstraintLayout>

SOLUTION: It ended up being a very dumb mistake, I realized I had left fetchUsers() method outside of the NewMessageActivity class, so I just moved that method back into the class and I was able to reference the RecyclerView component.

Answer 1

Define the reference to the RecyclerView using the code below before setting an adapter to it. ie

1. Outside onCreate function right above it within the class. Define your RecyclerView as below.

   lateinit var recycler_view_new_message: RecyclerView

2. Inside your onCreate function before recycler_view_new_message.adapter = adapter , add the code below.

   recycler_view_new_message = findViewById<RecyclerView>(R.id. recycler_view_new_message)