Kotlin Android studio :How to pass dataclass obj from one activity to another activity?

Question

Basically I have a activity which shows all the records input by the user. This uses a recyclerview. When the user clicks on an item row, it takes that info and displays it on the screen in another activity which is "Edit buy screen" . The user can edit the information and update it and then will be taken back to the "all records screen" upon success. using getIntent, I managed to show the info on the screen. However when I try to update the info it doesnt change. According to debug. The var studentModel(Dataclass obj) is null on the second activity. This tells me that i need a way to bring the studentModel obj data from allrecords activity to the editScreen activity. Any way i can do this using getIntent or another way?

All records class

private lateinit var edName: EditText
private lateinit var edEmail: Button
private lateinit var edBuyAmount: EditText
private lateinit var edUseAmount: EditText
private lateinit var edReason: EditText
private lateinit var btnAdd: Button
private lateinit var btnView: Button
private lateinit var btnUpdate: Button

private lateinit var sqLiteHelper: SQLiteHelper
private lateinit var recyclerView: RecyclerView
private  var adapter: StudentAdapter?=null
private var std:StudentModel?=null     <-------------This holds the data when the user clicks a row of data


@RequiresApi(Build.VERSION_CODES.N)
override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_all_recordpage)

    val textView: TextView =findViewById(R.id.DateText)
    val simpleDateFormat= SimpleDateFormat("yyyy/MM/dd\n   HH:mm", Locale.getDefault()).format(
        Date()
    )
    val currentDateAndTime: String = simpleDateFormat.format(Date())
    textView.text = currentDateAndTime

    val button = findViewById<Button>(R.id.goBackToHome)
    button.setOnClickListener{
        val intent = Intent(this,MainMenu::class.java)
        startActivity(intent)
    }

    initView()
    initRecyclerView()
    sqLiteHelper= SQLiteHelper(this)
    //Show recycler view
    val stdList = sqLiteHelper.getAllStudent()
    Log.e("おっけ","${stdList.size}")

    adapter?.setOnClickItem {

        //購入・使用編集画面に遷移

        if(it.buyamount > 0){
            val intent = Intent(this,buyDetailsScreen::class.java)
            intent.putExtra("date",it.email)
            intent.putExtra("name", it.name)
            intent.putExtra("buyAmount", it.buyamount)
    //----> (I assume I have to carry the var std to the next intent?)
            startActivity(intent)


        }else if (it.useamount > 0){
            val intent = Intent(this,useDetailsScreen::class.java)
            startActivity(intent)
            edName.setText(it.name)
            edEmail.text = it.email
            edUseAmount.setText(""+it.useamount)
            edReason.setText(it.reason)
            std = it

        }else{
            Toast.makeText(this,"エラーが発生しました",Toast.LENGTH_LONG).show()
        }

    }
    adapter?.addItems(stdList)
    adapter?.setOnClickDeleteItem{
        deleteStudent(it.id)
    }
}

private fun deleteStudent(id:Int){
    val builder = AlertDialog.Builder(this)
    builder.setMessage("データを削除してよろしいですか")
    builder.setCancelable(true)
    builder.setNegativeButton("いいえ"){dialog, _ ->
        dialog.dismiss()
    }
    builder.setPositiveButton("はい"){dialog, _ ->
        sqLiteHelper.deleteStudentById(id)
        getStudents()
        dialog.dismiss()
    }

    val alert = builder.create()
    alert.show()
}

private fun updateStudent(){
    val name = edName.text.toString()
    val email = edEmail.text.toString()
    val buyAmount = edBuyAmount.text.toString().toInt()
    val useAmount = edUseAmount.text.toString().toInt()
    val reason = edReason.text.toString()
    //Check record not changed
    if(name == std?.name && email == std?.email && buyAmount == std?.buyamount && useAmount == std?.useamount && reason == std?.reason){
        Toast.makeText(this,"データが変更されてない", Toast.LENGTH_SHORT).show()
        return
    }

    if(std == null) return
    val std = StudentModel(id=std!!.id,name = name,email = email, buyamount = buyAmount, useamount = useAmount, reason = reason)
    val status = sqLiteHelper.updateStudent(std)
    if(status > -1){
        clearEditText()
        getStudents()
    }else{
        Toast.makeText(this,"更新失敗した", Toast.LENGTH_SHORT).show()
    }


}
private fun getStudents(){
    val stdList = sqLiteHelper.getAllStudent()
    Log.e("おっけ","${stdList.size}")

    adapter?.addItems(stdList)
}
private fun addStudent(){
    val name = edName.text.toString()
    val email = edEmail.text.toString()
    val buyAmount = edBuyAmount.text.toString().toInt()
    val useAmount = edUseAmount.text.toString().toInt()
    val reason = edReason.text.toString()

    if(name.isEmpty()||email.isEmpty()|| buyAmount.toString().isEmpty() ||useAmount.toString().isEmpty() || reason.toString().isEmpty()){
        Toast.makeText(this,"データを入力してください", Toast.LENGTH_SHORT).show()
    }else{
        val std = StudentModel(name = name, email=email, buyamount=buyAmount, useamount=useAmount, reason = reason)
        val status = sqLiteHelper.insertStudent(std)
        //Check Insert success or not success
        if(status > -2){
            Toast.makeText(this,"データを追加しました。", Toast.LENGTH_SHORT).show()
            clearEditText()
        }else{
            Toast.makeText(this,"データが保存されてないようです。", Toast.LENGTH_SHORT).show()
        }
    }
}
private fun clearEditText(){
    edName.setText("")
    edEmail.text = ""
    edBuyAmount.setText("")
    edUseAmount.setText("")
    edReason.setText("")
    edName.requestFocus()
}
private fun initRecyclerView(){
    recyclerView.layoutManager=LinearLayoutManager(this)
    adapter = StudentAdapter()
    recyclerView.adapter=adapter
}
private fun initView(){
    recyclerView=findViewById(R.id.recyclerView)
}

}``

Student model data class

import java.util.* data class StudentModel( var id: Int=getAutoId(), var name: String = "", var email: String = "", var buyamount: Int = 0, var useamount: Int=0, var reason: String = "" )
{ companion object{ fun getAutoId():Int{ val random = Random() return random.nextInt(100) } } }

Buy details screen

class buyDetailsScreen : AppCompatActivity() {

private lateinit var edName: EditText
private lateinit var edEmail: Button
private lateinit var edBuyAmount: EditText
private lateinit var btnUpdate: Button

private lateinit var sqLiteHelper: SQLiteHelper
private lateinit var recyclerView: RecyclerView
private  var adapter: StudentAdapter?=null
private var std:StudentModel?= null    //Has nothing inside it . I need to get the info from first activity and put here


@SuppressLint("SetTextI18n")
override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_buy_details_screen)

    val button = findViewById<Button>(R.id.goBackToMain)
    button.setOnClickListener{
        val intent = Intent(this,allRecordpage::class.java)
        startActivity(intent)
    }
    val button2 = findViewById<Button>(R.id.goBacktoMain2)
    button2.setOnClickListener{
        val intent = Intent(this,allRecordpage::class.java)
        startActivity(intent)
    }
    initView()
    initRecyclerView()
    sqLiteHelper= SQLiteHelper(this)
    //Show recycler view
    val stdList = sqLiteHelper.getAllStudent()
    Log.e("おっけ","${stdList.size}")

    adapter?.addItems(stdList)

    edEmail = findViewById(R.id.edEmail)
    edEmail.setOnClickListener{
        clickDatePicker()
    }
    edEmail.text = intent.getStringExtra("date")
    edName.setText(intent.getStringExtra("name"))
    edBuyAmount.setText(""+(intent.getIntExtra("buyAmount",0)))

    btnUpdate.setOnClickListener{
        updateStudent()
        val intent = Intent(this,allRecordpage::class.java)
        startActivity(intent)
    }
}
private fun clickDatePicker() {
    val calender = Calendar.getInstance()
    val year = calender.get(Calendar.YEAR)
    val month = calender.get(Calendar.MONTH)
    val day = calender.get(Calendar.DAY_OF_MONTH)
    val datepicker = DatePickerDialog(this,
        {   view,selectedYear,selectedMonth,selectedDay ->
            val selectedDate = "$selectedYear/${selectedMonth+1}/$selectedDay"
            edEmail?.text=selectedDate
        },
        year,
        month,
        day
    )
    datepicker.datePicker.maxDate = System.currentTimeMillis()
    datepicker.show()
}
private fun updateStudent(){
    val name = edName.text.toString()
    val email = edEmail.text.toString()
    val buyAmount = edBuyAmount.text.toString().toInt()
    //Check record not changed
    if(name == std?.name && email == std?.email && buyAmount == std?.buyamount){
        Toast.makeText(this,"データが変更されてない", Toast.LENGTH_SHORT).show()
        return
    }

    if(std == null) return
    val std = StudentModel(id=std!!.id,name = name,email = email, buyamount = buyAmount )
    val status = sqLiteHelper.updateStudent(std)
    if(status > -1){
        clearEditText()
        getStudents()
    }else{
        Toast.makeText(this,"更新失敗した", Toast.LENGTH_SHORT).show()
    }
}
private fun getStudents(){
    val stdList = sqLiteHelper.getAllStudent()
    Log.e("おっけ","${stdList.size}")

    adapter?.addItems(stdList)
}
private fun clearEditText(){
    edName.setText("")
    edEmail.text = ""
    edBuyAmount.setText(0)
    edName.requestFocus()
}

private fun initRecyclerView(){
    recyclerView.layoutManager= LinearLayoutManager(this)
    adapter = StudentAdapter()
    recyclerView.adapter=adapter
}
private fun initView(){
    edName = findViewById(R.id.edName)
    edEmail = findViewById(R.id.edEmail)
    edBuyAmount = findViewById(R.id.edBuyAmount)
    btnUpdate=findViewById(R.id.btnUpdate)
    recyclerView=findViewById(R.id.recyclerView)

}