Obtain a crash message-App keeps stopping - kotlin

Question

I get the following trace error java.lang.ClassCastException: com.example.myhouse.MainActivity cannot be cast to com.brsthegck.kanbanboard.TasklistFragment$Callbacks at com.brsthegck.kanbanboard.TasklistFragment.onAttach(TasklistFragment.kt:52)at androidx.fragment.app.Fragment.performAttach(Fragment.java:2672) at androidx.fragment.app.FragmentStateManager.attach(FragmentStateManager.java:263) at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1170) at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1356)
enter image description here
Tasklist Fragment
private const val ARG_TASKLIST_TYPE = "tasklist_type"
private const val TASKLIST_TYPE_TODO = 0
private const val TASKLIST_TYPE_DOING = 1
private const val TASKLIST_TYPE_DONE = 2
class TasklistFragment : Fragment(){
private lateinit var visibleColorPaletteViewList : List<View>
lateinit var taskRecyclerView: RecyclerView
private var tasklistType : Int = -1
private var adapter : TaskViewAdapter? = TaskViewAdapter(LinkedList<Task>())
private var colorPaletteIsVisible : Boolean = false
private var callbacks: Callbacks? = null
//Callback interface to delegate access functions in MainActivity
interface Callbacks{
fun addTaskToViewModel(task: Task, destinationTasklistType: Int)
fun deleteTaskFromViewModel(tasklistType: Int, adapterPosition: Int)
fun getTaskListFromViewModel(tasklistType: Int) : LinkedList<Task>
}
//Attach context as a Callbacks reference to the callbacks variable when fragment attaches to container
override fun onAttach(context: Context) {
super.onAttach(context)
callbacks = activity as Callbacks? // error is here
}
//Detach context (assign to null) when fragment detaches from container
override fun onDetach() {
super.onDetach()
callbacks = null
}
//ItemTouchHelper instance with custom callback, to move task card view positions on hold
private val itemTouchHelper by lazy{
val taskItemTouchCallback = object : ItemTouchHelper.SimpleCallback(UP or DOWN, 0){
override fun onMove(recyclerView: RecyclerView,
viewHolder: RecyclerView.ViewHolder,
target: RecyclerView.ViewHolder): Boolean {
val adapter = recyclerView.adapter as TaskViewAdapter
val from = viewHolder.adapterPosition
val to = target.adapterPosition
adapter.moveTaskView(from, to)
adapter.notifyItemMoved(from, to)
return true
}
//Make taskview transparent while being moved
override fun onSelectedChanged(viewHolder: RecyclerView.ViewHolder?, actionState: Int) {
super.onSelectedChanged(viewHolder, actionState)
if(actionState == ACTION_STATE_DRAG)
viewHolder?.itemView?.alpha = 0.7f
}
//Make taskview opaque while being
override fun clearView(recyclerView: RecyclerView, viewHolder: RecyclerView.ViewHolder) {
super.clearView(recyclerView, viewHolder)
viewHolder.itemView.alpha = 1.0f
}
override fun onSwiped(viewHolder: RecyclerView.ViewHolder, direction: Int) { /* Not implemented on purpose. */ }
}
ItemTouchHelper(taskItemTouchCallback)
}
//Get the fragment arguments, tasklist type to be precise, and assign it to the member of this fragment
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
tasklistType = arguments?.getInt(ARG_TASKLIST_TYPE) as Int
}
//Inflate view of fragment, prepare recycler view and it's layout manager, and update the UI
override fun onCreateView(
inflater: LayoutInflater,
container: ViewGroup?,
savedInstanceState: Bundle?
): View?{
//Inflate the layout of this fragment, get recyclerview ref, set layout manager for recycler view
val view = inflater.inflate(R.layout.tasklist_fragment_layout, container,false)
taskRecyclerView = view.findViewById(R.id.task_recycler_view) as RecyclerView
taskRecyclerView.layoutManager = LinearLayoutManager(context)
itemTouchHelper.attachToRecyclerView(taskRecyclerView)
//Fill the recyclerview with data from viewmodel
updateInterface()
//Return the created view
return view
}
//Populate recyclerview and set up its adapter
private fun updateInterface(){
val tasks = callbacks!!.getTaskListFromViewModel(tasklistType)
adapter = TaskViewAdapter(tasks)
taskRecyclerView.adapter = adapter
}
Kanban class
class Kanban : Fragment(), TasklistFragment.Callbacks{
// TODO: Rename and change types of parameters
private var param1: String? = null
private var param2: String? = null
private lateinit var viewPager: ViewPager2
private lateinit var tabLayout: TabLayout
private lateinit var taskViewModel: TaskViewModel
//When add action bar button is pressed
override fun onOptionsItemSelected(item: MenuItem) = when(item.itemId) {
R.id.action_new_task -> {
val currentTasklistType = viewPager.currentItem
val currentTasklist = when (currentTasklistType) {
TASKLIST_TYPE_TODO -> taskViewModel.todoTaskList
TASKLIST_TYPE_DOING -> taskViewModel.doingTaskList
TASKLIST_TYPE_DONE -> taskViewModel.doneTaskList
else -> throw Exception("Unrecognized tasklist type")
}
val currentFragment = (activity?.supportFragmentManager?.fragments?.get(currentTasklistType) as TasklistFragment)
addTaskToViewModel(Task(), currentTasklistType)
currentFragment.taskRecyclerView.scrollToPosition(currentTasklist.size - 1)
true
}
else -> super.onOptionsItemSelected(item)
}
//Inflate the action bar menu resource on options menu creation
override fun onCreateOptionsMenu(menu: Menu, inflater: MenuInflater) {
inflater.inflate(R.menu.menu_action_bar, menu)
}
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
arguments?.let {
param1 = it.getString(ARG_PARAM1)
param2 = it.getString(ARG_PARAM2)
}
}
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
// Inflate the layout for this fragment
//Get viewmodel
val view: View = inflater.inflate(R.layout.fragment_kanban2, container, false)
taskViewModel = ViewModelProvider(this).get(TaskViewModel::class.java)
//Read tasklist data from shared prefs and populate viewmodel lists with it
readSharedPrefsToViewModel()
//Get ref to viewpager and set up its adapter & attributes
viewPager = view.findViewById(R.id.view_pager)
val viewPagerAdapter = TasklistFragmentStateAdapter(this)
viewPager.apply {
adapter = viewPagerAdapter
offscreenPageLimit = 2
//Get ref to tablayout, set up & attach its mediator
tabLayout = view.findViewById(R.id.tab_layout)
TabLayoutMediator(tabLayout, viewPager) { tab, position ->
tab.text = when (position) {
0 -> getString(R.string.tab_label_todo)
1 -> getString(R.string.tab_label_doing)
else -> getString(R.string.tab_label_done)
}
}.attach()
}
return view
}
override fun onStop() {
super.onStop()
writeViewModelToSharedPrefs()
}
//Adapter class for view pager
private inner class TasklistFragmentStateAdapter(fa: Kanban) : FragmentStateAdapter(fa){
override fun createFragment(position: Int): Fragment {
//Create argument bundle with task list type
val tasklistFragmentArguments = Bundle().apply{
putInt(ARG_TASKLIST_TYPE, position)
}
//Attach the argument bundle to new fragment instance and return the fragment
return TasklistFragment().apply{
arguments = tasklistFragmentArguments
}
}
override fun getItemCount(): Int = NUM_TASKLIST_PAGES
}
override fun addTaskToViewModel(task: Task, destinationTasklistType: Int) {
val destinationFragment = (activity?.supportFragmentManager?.fragments?.get(destinationTasklistType) as TasklistFragment)
val taskList = getTaskListFromViewModel(destinationTasklistType)
taskList.add(task)
destinationFragment.taskRecyclerView.adapter?.notifyItemInserted(taskList.size)
}
override fun deleteTaskFromViewModel(tasklistType: Int, adapterPosition: Int) {
val tasklistFragment = (activity?.supportFragmentManager?.fragments?.get(tasklistType) as TasklistFragment)
getTaskListFromViewModel(tasklistType).removeAt(adapterPosition)
tasklistFragment.taskRecyclerView.adapter?.notifyItemRemoved(adapterPosition)
}
override fun getTaskListFromViewModel(tasklistType: Int): LinkedList<Task> =
when(tasklistType){
TASKLIST_TYPE_TODO -> taskViewModel.todoTaskList
TASKLIST_TYPE_DOING -> taskViewModel.doingTaskList
TASKLIST_TYPE_DONE -> taskViewModel.doneTaskList
else -> throw Exception("Unrecognized tasklist type") }
private fun writeViewModelToSharedPrefs(){
val gson = Gson()
//Convert list to json string
val todoJSON = gson.toJson(taskViewModel.todoTaskList)
val doingJSON = gson.toJson(taskViewModel.doingTaskList)
val doneJSON = gson.toJson(taskViewModel.doneTaskList)
var sharedPref : SharedPreferences = requireActivity().getPreferences(Context.MODE_PRIVATE);
//Save json strings into shared preferences
activity?.getPreferences(MODE_PRIVATE)?.edit()?.apply {
putString(KEY_TODO_JSON, todoJSON)
putString(KEY_DOING_JSON, doingJSON)
putString(KEY_DONE_JSON, doneJSON)
}?.apply()
}
private fun readSharedPrefsToViewModel(){
val gson = Gson()
val sharedPrefs = activity?.getPreferences(MODE_PRIVATE)
val todoJSON = sharedPrefs?.getString(KEY_TODO_JSON, "[]")
val doingJSON = sharedPrefs?.getString(KEY_DOING_JSON, "[]")
val doneJSON = sharedPrefs?.getString(KEY_DONE_JSON, "[]")
val type = object: TypeToken<LinkedList<Task>>() {}.type //Gson requires type ref for generic types
taskViewModel.todoTaskList = gson.fromJson(todoJSON, type)
taskViewModel.doingTaskList = gson.fromJson(doingJSON, type)
taskViewModel.doneTaskList = gson.fromJson(doneJSON, type)
}
Main activity
public class MainActivity extends AppCompatActivity {
private TabLayout tabLayout;
private ViewPager2 viewPager2;
private MyFragment adapter;
private TextView register;
GridView contractorsGV;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
tabLayout = findViewById(R.id.tabLayout);
viewPager2 = findViewById(R.id.viewPager2);
tabLayout.addTab(tabLayout.newTab().setText("Home"));
tabLayout.addTab(tabLayout.newTab().setText("Idea Book"));
tabLayout.addTab(tabLayout.newTab().setText("My Profile"));
FragmentManager fragmentManager = getSupportFragmentManager();
adapter = new MyFragment(fragmentManager , getLifecycle());
viewPager2.setAdapter(adapter);
4. Fragment manager
public class MyFragment extends FragmentStateAdapter {
public MyFragment(#NonNull FragmentManager fm,Lifecycle lifecycle) {
super(fm,lifecycle);
}
#NonNull
#Override
public Fragment createFragment(int position) {
if(position==1)
{
return new Kanban();
}
if(position==2) {
return new signOut();
}
return new Navigation_Bar();
}