How to handle with "java.lang.NullPointerException: null cannot be cast to non-null type android.widget.TextView"?

Question

I'm new in android dev. So I decided to start making todo app. I wanted to make a window where a user may enter title and description of his tasks. After using fragment+recycler view I started to get this error: FATAL EXCEPTION: main Process: com.bignerdranch.android.taskmaster, PID: 8887 java.lang.RuntimeException: Unable to start activity ComponentInfo{com.bignerdranch.android.taskmaster/com.bignerdranch.android.taskmaster.MainActivity}: java.lang.NullPointerException: null cannot be cast to non-null type android.widget.TextView

But I cannot understand what is wrong. I've checked my MainActivity, Fragment and Adapter for recycler view. This error makes my app stop all the time. I would appreciate your help!

MainActivity.kt

package com.bignerdranch.android.taskmaster


import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.widget.TextView
import androidx.lifecycle.ViewModelProvider


import androidx.recyclerview.widget.LinearLayoutManager
import com.bignerdranch.android.taskmaster.databinding.ActivityMainBinding



class MainActivity : AppCompatActivity() {

    private lateinit var todoAdapter:TodoAdapter
    private lateinit var binding: ActivityMainBinding
    private lateinit var taskViewModel: TaskViewModel
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        binding = ActivityMainBinding.inflate(layoutInflater)

        setContentView(binding.root)
        val tvTodoTitle = findViewById<TextView>(R.id.tvTodoTitle)
        taskViewModel = ViewModelProvider(this).get(TaskViewModel::class.java)


        todoAdapter = TodoAdapter(mutableListOf())
        binding.rvTodoItems.adapter = todoAdapter
        binding.rvTodoItems.layoutManager = LinearLayoutManager(this)
        binding.btnAddTodo.setOnClickListener{
            NewTaskSheet().show(supportFragmentManager,"NewTaskTag")
            }
        taskViewModel.title.observe(this){
            tvTodoTitle.text=String.format("Task:%s",it)
        }

    }

}

NewTaskSheet

package com.bignerdranch.android.taskmaster

import android.os.Bundle

import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import androidx.lifecycle.ViewModelProvider
import com.bignerdranch.android.taskmaster.databinding.FragmentNewTaskSheetBinding
import com.google.android.material.bottomsheet.BottomSheetDialogFragment




class NewTaskSheet : BottomSheetDialogFragment(){

    private lateinit var binding: FragmentNewTaskSheetBinding
    private lateinit var taskViewModel: TaskViewModel


    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        binding = FragmentNewTaskSheetBinding.inflate(inflater,container,false)
        // Inflate the layout for this fragment
        return binding.root
    }

    override fun onViewCreated(view:View,savedInstanceState: Bundle?) {

        super.onCreate(savedInstanceState)
        val activity = requireActivity()
        taskViewModel= ViewModelProvider(activity).get(TaskViewModel::class.java)
        binding.btnSave.setOnClickListener{
            saveAction()
        }

    }



    private fun saveAction(){
        taskViewModel.title.value=binding.title.text.toString()
        taskViewModel.description.value=binding.description.text.toString()
        binding.title.setText("")
        binding.description.setText("")
        dismiss()
    }


}

TodoAdapter

package com.bignerdranch.android.taskmaster


import android.graphics.Paint.STRIKE_THRU_TEXT_FLAG

import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.CheckBox
import android.widget.TextView


import androidx.recyclerview.widget.RecyclerView
import com.bignerdranch.android.taskmaster.databinding.ItemTodoBinding



class TodoAdapter(
    private val todos: MutableList<Todo>
):RecyclerView.Adapter<TodoAdapter.TodoViewHolder>() {

    class TodoViewHolder( ItemTodoBinding: ItemTodoBinding): RecyclerView.ViewHolder(ItemTodoBinding.root)

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

        val layoutInflater = LayoutInflater.from(parent.context)
        val ItemTodoBinding = ItemTodoBinding.inflate(layoutInflater, parent, false)
        return TodoViewHolder(

            return TodoViewHolder(ItemTodoBinding)
        )


    }





    private fun toggleStrikeThrough(tvTodoTitle: TextView, isChecked:Boolean){
        if(isChecked){
            tvTodoTitle.paintFlags = tvTodoTitle.paintFlags or STRIKE_THRU_TEXT_FLAG
        }else{
            tvTodoTitle.paintFlags = tvTodoTitle.paintFlags and STRIKE_THRU_TEXT_FLAG.inv()
        }
    }

    override fun onBindViewHolder(holder: TodoViewHolder, position: Int) {
          val curTodo = todos[position]

          holder.itemView.apply{
              val tvTodoTitle = findViewById(R.id.tvTodoTitle) as TextView
              tvTodoTitle.text = curTodo.title

              val cbDone = findViewById(R.id.cbDone) as CheckBox
              cbDone.isChecked = curTodo.isChecked
              toggleStrikeThrough(tvTodoTitle, curTodo.isChecked)
              cbDone.setOnCheckedChangeListener { _, isChecked ->
                  toggleStrikeThrough(tvTodoTitle, isChecked)
                  curTodo.isChecked = !curTodo.isChecked


              }

              cbDone.setOnClickListener(View.OnClickListener{

                      todos.removeAll{todo->
                          todo.isChecked
                      }

                      notifyDataSetChanged()



              })

        }
    }

    override fun getItemCount(): Int {
          return todos.size
    }

}

activity_main

<?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"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/rvTodoItems"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        app:layout_constraintBottom_toTopOf="@+id/btnAddTodo"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />


    <Button
        android:id="@+id/btnAddTodo"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="20dp"
        android:text="Add"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toStartOf="@+id/btnTodoDone"
         />

    <Button
        android:id="@+id/btnTodoDone"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginEnd="8dp"
        android:text="Done"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent" />

</androidx.constraintlayout.widget.ConstraintLayout>

item_todo

<?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"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="80dp"
    android:paddingStart="8dp"
    android:paddingEnd="8dp">

    <TextView
        android:id="@+id/tvTodoTitle"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:text="Example"
        android:textSize="24sp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toStartOf="@+id/cbDone"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <CheckBox
        android:id="@+id/cbDone"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintTop_toTopOf="parent" />



</androidx.constraintlayout.widget.ConstraintLayout>

P.S The description of this error tells me that it is all in 25 line in MainActivity but I don't know what is the problem there. Thanks in advance

Answer 1

As you're using the View Binding feature there's no need to use this line to access your TextView

val tvTodoTitle = findViewById<TextView>(R.id.tvTodoTitle)

When you want to set your Title you can just do

binding.tvTodoTitle.text = "....."

That's assuming that a TextView with the name tvTodoTitle exists in activity_main