Виртуальный метод, вызываемый по нулевой ссылке на объект

Question

Пытаюсь создать recyclerview в андроид студийном проекте. Однако, когда я пытаюсь протестировать проект, я сталкиваюсь с ошибкой,

D/Diagnise: Attempt to invoke virtual method 'void android.support.v7.widget.RecyclerView.setLayoutManager(android.support.v7.widget.RecyclerView$LayoutManager)' on a null object reference

Сначала я вложил RecyclerView в RelativeLayout и столкнулся с исключением. Затем изменил весь макет на RecyclerView.

пакет smartpoultry.cocis.smartpoutry

import android.content.Context
import android.support.v7.app.AppCompatActivity
import android.os.Bundle
import android.support.v7.widget.LinearLayoutManager
import android.support.v7.widget.RecyclerView
import android.util.Log
import android.view.*
import android.widget.TextView

private val TAG : String = Diagnise ::class.java.simpleName

class Diagnise : AppCompatActivity() {
    private lateinit var recyclerView : RecyclerView
    private lateinit var adapterView : RecyclerView.Adapter<*>
    private lateinit var viewManager : RecyclerView.LayoutManager

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        requestWindowFeature(Window.FEATURE_LEFT_ICON)
        val actionBar = supportActionBar
        actionBar!!.setDisplayHomeAsUpEnabled(true)
        actionBar!!.title = "DIAGNOSIS"
        setContentView(R.layout.activity_diagnise)
        try {
            populateSymptoms()
        } catch(e : Exception) {
            Log.d(TAG, e.message)
        }
    }

    override  fun onOptionsItemSelected(item: MenuItem?): Boolean {
        when(item?.itemId) {
            android.R.id.home -> {
                onBackPressed()
                return true
            }
            else -> return super.onOptionsItemSelected(item)

        }
    }

    fun getUserName() {
        val userDetails = getSharedPreferences("user_details", Context.MODE_PRIVATE)
        val userID = userDetails.getLong("userID", -1)
        val userData = ExtendsDatabaseHandler(this)
        //statNotificationMessage?.text = "Hi " + userData.getUserDataById(GetUserNameModel(userID)) + "Error occured."
    }

    fun populateSymptoms() {
        var dataSet = mutableListOf("One", "Two")
        viewManager = LinearLayoutManager(this)
        adapterView = MyDataAdapter(dataSet)
        recyclerView = findViewById<RecyclerView>(R.id.scrollable).apply{
            //setHasFixedSize(true)
            layoutManager = viewManager
            adapter = adapterView
        }
    }}

Адаптер

class MyDataAdapter(private val data : MutableList<String>) : RecyclerView.Adapter<MyDataAdapter.ViewHolder>() {
    inner class ViewHolder (view : View) : RecyclerView.ViewHolder(view) {
        //Get view reference
        var textViewId = view.findViewById<TextView>(R.id.symptomTextData)
    }

    override fun onCreateViewHolder(p0: ViewGroup, p1: Int): ViewHolder {
        // create view holder to hold reference
        return ViewHolder(LayoutInflater.from(p0.context).inflate(R.layout.symptoms_lay_out, p0, false))
    }

    override fun onBindViewHolder(p0: ViewHolder, p1: Int) {
        //Lets add data to our reference
        p0.textViewId.text = data[p1]
    }

    //Getting size of our data.
    override fun getItemCount() =  data.size}

// Мои макеты

//activity_diagnise.xml
<?xml version="1.0" encoding="utf-8"?>
<android.support.v7.widget.RecyclerView
        xmlns:android="http://schemas.android.com/apk/res/android"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        xmlns:app="http://schemas.android.com/apk/res-auto"
        android:backgroundTint="#96FFFFFF"
        android:backgroundTintMode="src_over"
        android:id="@+id/scrollable"
        android:background="@drawable/splash_bg_2"
>

 //symptoms_lay_out.xml
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
              android:layout_width="match_parent"
              android:layout_height="match_parent">
    <TextView
            android:text="@string/symptomsData"
            android:layout_width="0dp"
            android:layout_height="92dp" android:id="@+id/symptomTextData" android:layout_weight="1"/>
</RelativeLayout>
</android.support.v7.widget.RecyclerView>

Я ожидаю некоторого вывода на экран. Большое вам спасибо

Answer 1

Пожалуйста, измените ваш XML следующим образом:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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=".DiagniseActivity">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="vertical">

        <android.support.v7.widget.RecyclerView
            xmlns:android="http://schemas.android.com/apk/res/android"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            xmlns:app="http://schemas.android.com/apk/res-auto"
            android:backgroundTint="#96FFFFFF"
            android:backgroundTintMode="src_over"
            android:id="@+id/scrollable"/>

    </LinearLayout>
</LinearLayout>

, и вы забыли поставить setContentView Activity:

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