kotlin adapter give me error in mainactivity - android-studio

Question

I have a class called medicine, I got an error when writing adapter = MedicineAdapter(this, this.medicineList!!) in main activity I saw the error in run window.
My app is crashing when I want to run and I saw one error which is about adapter's line
Also, I have medicine_items it is my custom design I assigned it to the adapter in my adapter also I checked my ids but ı don t know why am I got an error
MainActivity
class MainActivity : AppCompatActivity() {
private var adapter: MedicineAdapter? = null
private var medicineList : ArrayList<Medicine>? = null
private var recyclerView: RecyclerView? = null
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
recyclerView =
findViewById<View>(R.id.recycler) as RecyclerView
adapter = MedicineAdapter(this, this.medicineList!!)
val layoutManager = LinearLayoutManager(applicationContext)
recyclerView!!.layoutManager = layoutManager
recyclerView!!.itemAnimator = DefaultItemAnimator()
// Add a neat dividing line between items in the list
recyclerView!!.addItemDecoration(
DividerItemDecoration(this,
LinearLayoutManager.VERTICAL))
// set the adapter
recyclerView!!.adapter = adapter
}
override fun onCreateOptionsMenu(menu: Menu): Boolean {
menuInflater.inflate(R.menu.menu, menu)
return true
}
override fun onOptionsItemSelected(item: MenuItem): Boolean = when (item.itemId) {
R.id.addBtn -> {
val intent = Intent(this,AddNewMedicine::class.java)
startActivity(intent)
true
}
else -> super.onOptionsItemSelected(item)
}
fun addMedicine(m: Medicine){
medicineList!!.add(m)
adapter!!.notifyDataSetChanged()
}
}
MyAdapter
class MedicineAdapter(
private val mainActivity: MainActivity,
private val medicineList: ArrayList<Medicine>)
: RecyclerView.Adapter<MedicineAdapter.ListItemHolder>(){
override fun onCreateViewHolder(
parent: ViewGroup, viewType: Int): ListItemHolder {
val itemView = LayoutInflater.from(parent.context).inflate(R.layout.medicine_items, parent, false)
return ListItemHolder(itemView)
}
inner class ListItemHolder(view: View) :
RecyclerView.ViewHolder(view),
View.OnClickListener {
internal var name = view.findViewById<TextView>(R.id.name)
internal var amount = view.findViewById<TextView>(R.id.amount)
internal var description = view.findViewById<TextView>(R.id.description)
init {
view.isClickable = true
view.setOnClickListener(this)
}
override fun onClick(view: View) {
//val intentToCarPager = Intent(view!!.context, CarPagerActivity::class.java)
//view.context.startActivity(intentToCarPager)
}
}
override fun onBindViewHolder(holder: ListItemHolder, position: Int) {
val medicine = medicineList!![position]
holder.name.text = medicine.name.toString()
holder.amount.text = medicine.amount.toString()
holder.description.text = medicine.desription.toString()
}
override fun getItemCount(): Int {
if (medicineList != null) {
return medicineList.size
}
return -1
}
}
my run window

Answer 1

It's because here:
private var medicineList : ArrayList<Medicine>? = null
you have initialized medicineList as null and you haven't given it a proper value along the way and here:
adapter = MedicineAdapter(this, this.medicineList!!)
you have asserted that it is not null and tried to assign it to the adapter.
If you have no elements to add to your array at first, initialize it this way:
private var medicineList : ArrayList<Medicine> = arrayListOf()
and then you can add elements to it:
medicineList.add(myMedicine)