我正在使用viewpager，并且在viewpager的一个片段中，我附加了recylerview并得到了这个nullpointer异常

问：

[Image of my code that is showing null pointer exception][1]


  [1]: https://i.stack.imgur.com/z9C6o.png

the fragment code->
<?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"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/rv"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>

->the activity code
package com.example.mymu

import android.graphics.Color
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import androidx.recyclerview.widget.LinearLayoutManager
import androidx.recyclerview.widget.RecyclerView
import androidx.viewpager.widget.ViewPager

import com.example.my.MusicInfo
import com.example.my.PageAdapter
import kotlinx.android.synthetic.main.activity_main2.*

class MainActivity2 : AppCompatActivity() {


    companion object {
        lateinit var mylist: MutableList<MusicInfo>
    }

    override fun onCreate(savedInstanceState: Bundle?) {

        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main2)

        val song1= MusicInfo("Darshan Raval","Asal Main",R.drawable.asalmain,"3:10")
        val song2=MusicInfo("Jass Manak","Prada", R.drawable.manak,"2:50")
        val song3=MusicInfo("Darshan Raval","Asal Main",R.drawable.asalmain,"3:10")
        val song4=MusicInfo("Jass Manak","Prada",R.drawable.manak,"2:50")
        val song5=MusicInfo("Darshan Raval","Asal Main",R.drawable.asalmain,"3:10")
        val song6=MusicInfo("Jass Manak","Prada",R.drawable.manak,"2:50")
        val song7=MusicInfo("Darshan Raval","Asal Main",R.drawable.asalmain,"3:10")
        val song8=MusicInfo("Jass Manak","Prada",R.drawable.manak,"2:50")
        val song9=MusicInfo("Darshan Raval","Asal Main",R.drawable.asalmain,"3:10")
        val song10=MusicInfo("Jass Manak","Prada",R.drawable.manak,"2:50")
        val song11=MusicInfo("Darshan Raval","Asal Main",R.drawable.asalmain,"3:10")
        val song12=MusicInfo("Jass Manak","Prada",R.drawable.manak,"2:50")
        val song13=MusicInfo("Darshan Raval","Asal Main",R.drawable.asalmain,"3:10")
        val song14=MusicInfo("Jass Manak","Prada",R.drawable.manak,"2:50")
        val song15=MusicInfo("Darshan Raval","Asal Main",R.drawable.asalmain,"3:10")
        val song16=MusicInfo("Jass Manak","Prada",R.drawable.manak,"2:50")
        val song17=MusicInfo("Darshan Raval","Asal Main",R.drawable.asalmain,"3:10")
        val song18=MusicInfo("Jass Manak","Prada",R.drawable.manak,"2:50")
        val song19=MusicInfo("Darshan Raval","Asal Main",R.drawable.asalmain,"3:10")
        val song20=MusicInfo("Jass Manak","Prada",R.drawable.manak,"2:50")
        mylist= mutableListOf()
        mylist.add(song1)
        mylist.add(song2)
        mylist.add(song3)
        mylist.add(song4)
        mylist.add(song5)
        mylist.add(song6)
        mylist.add(song7)
        mylist.add(song8)
        mylist.add(song9)
        mylist.add(song10)
        mylist.add(song11)
        mylist.add(song12)
        mylist.add(song13)
        mylist.add(song14)
        mylist.add(song15)
        mylist.add(song16)
        mylist.add(song17)
        mylist.add(song18)
        mylist.add(song19)
        mylist.add(song20)
    
//this is the part where it is showing error//

val recyclerView=findViewById（R.id.rv） recyclerView.layoutManager = LinearLayoutManager（this@MainActivity2，LinearLayoutManager.VERTICAL，false） recyclerView.adapter = MyAdapter（我的列表） view_pager.adapter=PageAdapter（supportFragmentManager） tab_layout.setupWithViewPager（view_pager） tab_layout.setTabTextColors（Color.parseColor（“#7DC1C6”），resources.getColor（R.color.teal_700）） tab_layout.setBackgroundResource（R.drawable.drawable4）

    }
}``