How can I use recycler viewer with a fragment on a tablayout (android studio Kotlin)?

Issue

The error in "adapter = UserAdapter(users)" says type mismatch required: context "Change parameter Context type of primary constructor of class UserAdapter to ArrayList" I tried running it while the "adapter = UserAdapter(users)" is enclosed as a comment (like so //adapter = UserAdapter(users)) in shows an error in logcat saying "java.lang.NullPointerException: v.findViewById(R.id.RVusermain) must not be null at com.example.chattrialskot.fragments.Year1.onCreateView(Year1.kt:49) ".

USERS.kt

class Users {

var userstuID: String? = null;
var username: String? = null;
var useremail: String? = null;
var useraccstat: String? = null;
var useruid: String? = null;
var useryear: String? = null;

constructor(){}

constructor(userstuID: String?, username: String?, useremail: String?, useraccstat: String?,
            useruid: String?, useryear: String?){

    this.userstuID = userstuID
    this.username = username
    this.useremail = useremail
    this.useraccstat = useraccstat
    this.useruid = useruid
    this.useryear = useryear
} }

USER ADAPTER

class UserAdapter(var UAContext: Context, var userlist: ArrayList<Users>):
    RecyclerView.Adapter<UserAdapter.UsersViewHolder> (){

fun UserAdapter(userlist: ArrayList<Users>, mContext: Context){

    this.userlist = userlist
    this.UAContext = mContext
}

override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): UsersViewHolder {

    val view:View = LayoutInflater.from(UAContext).inflate(
        R.layout.userlayout, parent,
        false)
    return UserAdapter.UsersViewHolder(view)

}

FRAGMENT

class Year1 : Fragment() {

companion object {
    fun newInstance(): Year1 {
        return Year1()
    }
}

override fun onCreateView(
    inflater: LayoutInflater, container: ViewGroup?,
    savedInstanceState: Bundle?
): View? {
    // Inflate the layout for this fragment
    val v = inflater.inflate(R.layout.fragment_year1, container, false)

    userrecyclerviewer = v.findViewById<RecyclerView>(R.id.RVyear1)
    userrecyclerviewer.setHasFixedSize(true)
    userrecyclerviewer.layoutManager = LinearLayoutManager(context)
    userrecyclerviewer.adapter = adapter

    users = ArrayList()
    adapter = UserAdapter(users) 
    getUsers()
    return v
}

private fun getUsers(){

    FireAuth = FirebaseAuth.getInstance()
    FireDB = FirebaseDatabase.getInstance().getReference()

    FireDB.child("users").addValueEventListener(object: ValueEventListener{

        override fun onDataChange(snapshot: DataSnapshot) {

            users.clear()

            for(postSnapshot in snapshot.children){

                val userfrmDB = postSnapshot.getValue(Users::class.java)

                if(FireAuth.currentUser?.uid != userfrmDB?.useruid
                    && userfrmDB?.useraccstat != "Banned")
                {
                    users.add(userfrmDB!!)
                }
            }
            adapter.notifyDataSetChanged()
        }
        override fun onCancelled(error: DatabaseError) {
        }
    })
}

override fun onCreate(savedInstanceState: Bundle?) {

    super.onCreate(savedInstanceState)
}}

Solution

class Year1 : Fragment() {

companion object {
  fun newInstance(): Year1 {
      return Year1()
  } 
}

override fun onCreateView(
    inflater: LayoutInflater, container: ViewGroup?,
    savedInstanceState: Bundle?
 ): View? {
    // Inflate the layout for this fragment
    val v = inflater.inflate(R.layout.fragment_year1, container, false)

    userrecyclerviewer = v.findViewById<RecyclerView>(R.id.RVusermain)
    userrecyclerviewer.setHasFixedSize(true)
    getUsers()
    users = ArrayList()
    userrecyclerviewer.layoutManager = LinearLayoutManager(context)
    adapter = UserAdapter(context?, users) 
    userrecyclerviewer.adapter = adapter

    return v
}

private fun getUsers(){

   FireAuth = FirebaseAuth.getInstance()
   FireDB = FirebaseDatabase.getInstance().getReference()

   FireDB.child("users").addValueEventListener(object: ValueEventListener{

    override fun onDataChange(snapshot: DataSnapshot) {

        users.clear()

        for(postSnapshot in snapshot.children){

            val userfrmDB = postSnapshot.getValue(Users::class.java)

            if(FireAuth.currentUser?.uid != userfrmDB?.useruid
                && userfrmDB?.useraccstat != "Banned")
            {
                users.add(userfrmDB!!)
            }
        }
        adapter.notifyDataSetChanged()
    }
    override fun onCancelled(error: DatabaseError) {
    }
  })
}

 override fun onCreate(savedInstanceState: Bundle?) {

    super.onCreate(savedInstanceState)
 }}

You were getting Nullpointer exception because you were setting adapter even it has been initialized. Please, follow the code above.

Answered By - Rudra Rokaya