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Android Studio – How do I ensure lateinit variable initialization before it is needed?

I have an app that launches the majority of the time, but every 7 or so launches it crashes with the error:

kotlin.UninitializedPropertyAccessException: lateinit property weekdayList has not been initialized

This is a clear error, I’m just not sure how to ensure the variable is initialized early enough in the context of my app.

Things I have tried

  • I tried moving variables around, making "inner" and "outer"
    variables, one within onCreate and an underscore led variable as
    the class variable.

  • Changing the viewmodel so that it will wait until the call to the db has finished (I
    couldn’t make this work, but mostly because I wasn’t sure how to do it).

I think the problem is in the onCreate function, and that the weekday observe isn’t setting the value of the variable faster than the task observe (where the weekdayList variable is needed) is called?

Edit 1

I referenced this but I end up with a similar error

java.lang.IndexOutOfBoundsException: Empty list doesn’t contain element at index 1.

Edit 2

I understand how lateinit variables and nullables work at this point, I want to try and clarify this a little better.

The variable weekdayList needs to be initialized to the correct list before I hit the observe for the taskList, otherwise the app will crash.

I have tried setting the variable to be nullable, and Iend up with:

  • skipping parts of the program when it’s null (not an option)
  • crashing with a null pointer exception (if set to non-nullable)
  • no tasks get assigned to any day, which means no recyclerviews get updated, thus making the app appear to contain no tasks when it does.
  • weekday buttons that don’t work because there is no weekdayList for them to compare against to launch the next activity

My problem doesn’t stand in figuring out if it’s null or not, it’s trying to guarantee that it won’t be null.

Sorry for the confusion

Main Activity

class MainActivity : AppCompatActivity() {
    private lateinit var binding: ActivityMainBinding
    private val plannerViewModel: PlannerViewModel by viewModels {
        PlannerViewModelFactory((application as PlannerApplication).repository)
    }

    private var weekdayList: List<Weekday> = listOf()
    private var taskList: List<Task> = listOf()
    private var taskDayList = mutableListOf<Task>()

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        binding = ActivityMainBinding.inflate(layoutInflater)
        setContentView(binding.root)

        val clearButtonText = binding.clearCardText
        val sundayButtonText = binding.sundayCardText
        val mondayButtonText = binding.mondayCardText
        val tuesdayButtonText = binding.tuesdayCardText
        val wednesdayButtonText = binding.wednesdayCardText
        val thursdayButtonText = binding.thursdayCardText
        val fridayButtonText = binding.fridayCardText
        val saturdayButtonText = binding.saturdayCardText
        val sundayRv: RecyclerView = binding.sundayRv
        val sundayAdapter = TaskRvAdapter(null)
        sundayRv.adapter = sundayAdapter
        sundayRv.layoutManager = LinearLayoutManager(this)
        val mondayRv: RecyclerView = binding.mondayRv
        val mondayAdapter = TaskRvAdapter(null)
        mondayRv.adapter = mondayAdapter
        mondayRv.layoutManager = LinearLayoutManager(this)
        val tuesdayRv: RecyclerView = binding.tuesdayRv
        val tuesdayAdapter = TaskRvAdapter(null)
        tuesdayRv.adapter = tuesdayAdapter
        tuesdayRv.layoutManager = LinearLayoutManager(this)
        val wednesdayRv: RecyclerView = binding.wednesdayRv
        val wednesdayAdapter = TaskRvAdapter(null)
        wednesdayRv.adapter = wednesdayAdapter
        wednesdayRv.layoutManager = LinearLayoutManager(this)
        val thursdayRv: RecyclerView = binding.thursdayRv
        val thursdayAdapter = TaskRvAdapter(null)
        thursdayRv.adapter = thursdayAdapter
        thursdayRv.layoutManager = LinearLayoutManager(this)
        val fridayRv: RecyclerView = binding.fridayRv
        val fridayAdapter = TaskRvAdapter(null)
        fridayRv.adapter = fridayAdapter
        fridayRv.layoutManager = LinearLayoutManager(this)
        val saturdayRv: RecyclerView = binding.saturdayRv
        val saturdayAdapter = TaskRvAdapter(null)
        saturdayRv.adapter = saturdayAdapter
        saturdayRv.layoutManager = LinearLayoutManager(this)


        // Setting day card names
        clearButtonText.text = "Clear"
        sundayButtonText.text = "Sun"
        mondayButtonText.text = "Mon"
        tuesdayButtonText.text = "Tue"
        wednesdayButtonText.text = "Wed"
        thursdayButtonText.text = "Thu"
        fridayButtonText.text = "Fri"
        saturdayButtonText.text = "Sat"
        sundayButtonText.text = "Sun"

        plannerViewModel.allWeekdays.observe(this, {
            weekdayList = it
        })

        plannerViewModel.allTasks.observe(this, { tasks ->
            taskList = tasks
            taskDayList = mutableListOf()

            for (i in 1..7) {

                taskDayList = sortTasks(weekdayList[i], taskList)

                when (i) {
                    1 -> {
                        sundayAdapter.submitList(taskDayList)
                        toggleVisibility(taskDayList, binding.sundayInner,
                                binding.sundayCardText, sundayRv, binding.sundayNoTasks)
                    }
                    2 -> {
                        mondayAdapter.submitList(taskDayList)
                        toggleVisibility(taskDayList, binding.mondayInner,
                                binding.mondayCardText, mondayRv, binding.mondayNoTasks)
                    }
                    3 -> {
                        tuesdayAdapter.submitList(taskDayList)
                        toggleVisibility(taskDayList, binding.tuesdayInner,
                                binding.tuesdayCardText, tuesdayRv, binding.tuesdayNoTasks)
                    }
                    4 -> {
                        wednesdayAdapter.submitList(taskDayList)
                        toggleVisibility(taskDayList, binding.wednesdayInner,
                                binding.wednesdayCardText, wednesdayRv, binding.wednesdayNoTasks)
                    }
                    5 -> {
                        thursdayAdapter.submitList(taskDayList)
                        toggleVisibility(taskDayList, binding.thursdayInner,
                                binding.thursdayCardText, thursdayRv, binding.thursdayNoTasks)
                    }
                    6 -> {
                        fridayAdapter.submitList(taskDayList)
                        toggleVisibility(taskDayList, binding.fridayInner,
                                binding.fridayCardText, fridayRv, binding.fridayNoTasks)
                    }
                    7 -> {
                        saturdayAdapter.submitList(taskDayList)
                        toggleVisibility(taskDayList, binding.saturdayInner,
                                binding.saturdayCardText, saturdayRv, binding.saturdayNoTasks)
                    }
                }
            }
        })
    }

    private fun toggleVisibility(taskDayList: List<Task>, inner: ConstraintLayout,
                                 cardText: View, rv: RecyclerView, noTask: View) {
        if (taskDayList.count() == 0 ) {
            val newConstraintSet = ConstraintSet()
            newConstraintSet.clone(inner)
            newConstraintSet.connect(noTask.id, ConstraintSet.TOP,
                    cardText.id, ConstraintSet.BOTTOM)
            newConstraintSet.applyTo(inner)

            newConstraintSet.connect(cardText.id, ConstraintSet.BOTTOM,
                    noTask.id, ConstraintSet.TOP)
            newConstraintSet.applyTo(inner)

            rv.visibility = View.GONE
            noTask.visibility = View.VISIBLE

            Log.i("this", "ran zero")
        } else {
            val newConstraintSet = ConstraintSet()
            newConstraintSet.clone(inner)
            newConstraintSet.connect(rv.id, ConstraintSet.TOP,
                    cardText.id, ConstraintSet.BOTTOM)
            newConstraintSet.applyTo(inner)

            newConstraintSet.connect(cardText.id, ConstraintSet.BOTTOM,
                    rv.id, ConstraintSet.TOP)
            newConstraintSet.applyTo(inner)

            rv.visibility = View.VISIBLE
            noTask.visibility = View.GONE

            Log.i("this", "ran else")
        }
    }

    private fun sortTasks(day: Weekday, tasks: List<Task>): MutableList<Task> {
        val newAdapterList = mutableListOf<Task>()

        tasks.forEach {
            if (it.weekdayId == day.id) {
                newAdapterList.add(it)
            }
        }

        return newAdapterList
    }

    private fun startWeekdayActivity(day: Weekday) {
        val intent = Intent(this, WeekdayActivity::class.java)
        intent.putExtra("dayId", day.id)
        this.startActivity(intent)
    }

    private fun clearDb(taskList: List<Task>) {
        val alertDialog: AlertDialog = this.let { outerIt ->
            val builder = AlertDialog.Builder(outerIt)
            builder.apply {
                setPositiveButton("Clear",
                        DialogInterface.OnClickListener { dialog, id ->
                            if (taskList.count() == 0) {
                                Toast.makeText(context, "No tasks to clear", Toast.LENGTH_SHORT).show()
                            } else {
                                plannerViewModel.deleteAllTasks()
                                Toast.makeText(context, "Tasks cleared", Toast.LENGTH_SHORT).show()
                            }
                        })
                setNegativeButton("Cancel",
                        DialogInterface.OnClickListener { dialog, id ->
                            // User cancelled the dialog
                        })
            }
                    .setTitle("Clear tasks?")
                    .setMessage("Are you sure you want to clear the weeks tasks?")

            builder.create()
        }

        alertDialog.show()
    }

    private fun checkDay(dayIn: String, weekdayList: List<Weekday>) {
        weekdayList.forEach {
            if (dayIn == "clear_card" && it.day == "Clear") {
                clearDb(taskList)
            } else {
                val dayInAbr = dayIn.substring(0, 3).toLowerCase(Locale.ROOT)
                val dayOutAbr = it.day.substring(0, 3).toLowerCase(Locale.ROOT)

                if (dayInAbr == dayOutAbr) {
                    startWeekdayActivity(it)
                }
            }
        }
    }

    fun buttonClick(view: View) {
        when (view.id) {
            R.id.clear_card -> checkDay(view.context.resources.getResourceEntryName(R.id.clear_card).toString(), weekdayList)
            R.id.sunday_card -> checkDay(view.context.resources.getResourceEntryName(R.id.sunday_card).toString(), weekdayList)
            R.id.monday_card -> checkDay(view.context.resources.getResourceEntryName(R.id.monday_card).toString(), weekdayList)
            R.id.tuesday_card -> checkDay(view.context.resources.getResourceEntryName(R.id.tuesday_card).toString(), weekdayList)
            R.id.wednesday_card -> checkDay(view.context.resources.getResourceEntryName(R.id.wednesday_card).toString(), weekdayList)
            R.id.thursday_card -> checkDay(view.context.resources.getResourceEntryName(R.id.thursday_card).toString(), weekdayList)
            R.id.friday_card -> checkDay(view.context.resources.getResourceEntryName(R.id.friday_card).toString(), weekdayList)
            R.id.saturday_card -> checkDay(view.context.resources.getResourceEntryName(R.id.saturday_card).toString(), weekdayList)
        }
    }
}

Viewmodel

class PlannerViewModel(private val repository: DbRepository) : ViewModel() {
    val allWeekdays: LiveData<List<Weekday>> = repository.allWeekdays.asLiveData()
    val allTasks: LiveData<List<Task>> = repository.allTasks.asLiveData()

    fun insertWeekday(weekday: Weekday) = viewModelScope.launch {
        repository.insertWeekday(weekday)
    }

    fun insertTask(task: Task) = viewModelScope.launch {
        repository.insertTask(task)
    }

    fun deleteTask(task: Task) = viewModelScope.launch {
        repository.deleteTask(task)
    }

    fun deleteAllTasks() = viewModelScope.launch {
        repository.deleteAllTasks()
    }
}

class PlannerViewModelFactory(private val repository: DbRepository) : ViewModelProvider.Factory {
    override fun <T : ViewModel?> create(modelClass: Class<T>): T {
        if (modelClass.isAssignableFrom(PlannerViewModel::class.java)) {
            @Suppress("UNCHECKED_CAST")
            return PlannerViewModel(repository) as T
        }
        throw IllegalArgumentException("Unknown ViewModel class")
    }
}
Tags:

5

Answers


  1. Chosen as BEST ANSWER
    0

    A solution with help from cactustictacs in the comments.

    I moved a lot of the list dependency to a new function called setAdapterList. this allows both observes to run the function, and only the one with both lists initialized will run the code contained. I kept the variables lateinit and it seems to be working so far!

    The Main Change in Main Activity

    ...

private fun setAdapterLists(adapterList: List<TaskRvAdapter>, rvList: List<RecyclerView>) {
        if (this::weekdayList.isInitialized  && this::taskList.isInitialized) {
            adapterList.forEach {
                taskDayList = mutableListOf()
                val i = adapterList.indexOf(it)
                taskDayList = sortTasks(weekdayList[i + 1], taskList)

                Log.i("rvli", rvList[i].toString())

                when (i) {
                    0 -> {
                        adapterList[i].submitList(taskDayList)
                        toggleVisibility(taskDayList, binding.sundayInner,
                                binding.sundayCardText, rvList[i], binding.sundayNoTasks)
                    }
                    1 -> {
                        adapterList[i].submitList(taskDayList)
                        toggleVisibility(taskDayList, binding.mondayInner,
                                binding.mondayCardText, rvList[i], binding.mondayNoTasks)
                    }
                    2 -> {
                        adapterList[i].submitList(taskDayList)
                        toggleVisibility(taskDayList, binding.tuesdayInner,
                                binding.tuesdayCardText, rvList[i], binding.tuesdayNoTasks)
                    }
                    3 -> {
                        adapterList[i].submitList(taskDayList)
                        toggleVisibility(taskDayList, binding.wednesdayInner,
                                binding.wednesdayCardText, rvList[i], binding.wednesdayNoTasks)
                    }
                    4 -> {
                        adapterList[i].submitList(taskDayList)
                        toggleVisibility(taskDayList, binding.thursdayInner,
                                binding.thursdayCardText, rvList[i], binding.thursdayNoTasks)
                    }
                    5 -> {
                        adapterList[i].submitList(taskDayList)
                        toggleVisibility(taskDayList, binding.fridayInner,
                                binding.fridayCardText, rvList[i], binding.fridayNoTasks)
                    }
                    6 -> {
                        adapterList[i].submitList(taskDayList)
                        toggleVisibility(taskDayList, binding.saturdayInner,
                                binding.saturdayCardText, rvList[i], binding.saturdayNoTasks)
                    }
                }
            }
        }
    }
    

...

  2. 0

    A variable declared as lateinit just means that you are sure that when the object is dereferenced it will not be null. In your case you are calling a method from weekdayList object before it is assigned a value. It is important to understand the concept clearly and why your code works.

    Happy Coding!

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  3. 0

    You can use the "isInitialized" method, for checking "lateinit" variable is initialized or not.

    Please refer the below article for the this-

    https://blog.mindorks.com/how-to-check-if-a-lateinit-variable-has-been-initialized

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  4. 0

    lateinit is a way for you to have a var without an initial value when you declare it. It’s a nice way to avoid taking something that will never be null, and making it nullable (and having to null check it forever) just so you can temporarily set it to null as a placeholder that nothing will ever see.

    What you’re doing is promising the compiler "ok, I’m not going to provide a value when the class is constructed, but I promise I’ll set it to something before anything tries to read it". You’re telling the compiler to trust you, that you know how your code works, and you can guarantee it’ll all be ok.

    Your problem is that it seems you can’t guarantee that things won’t try to read that property before you write to it. Your state can either be "has a value", or "doesn’t have a value", and the rest of your code could encounter either state.

    The "no value" state is basically null, so you should probably make the variable nullable instead, and initialise it as null. Kotlin has all that nice null-safety stuff to help your code handle it, until you do get a value. lateinit seems like the wrong tool for the job, even if you check ::isInitialized it’s just making your life a lot harder when the null-checking stuff is right there!

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  5. 0

    Use lazy properties , refer to this doc for more informations:

    assuming weekDayList is the property you want to successfully initialize ->

    private var weekDayList: List<WeekDay> by lazy {
    //return your first value
    listOf<WeekDay>()
}

    Here is a useful link about LifeCycleAware Lazy properties: blog Although, it is not required.

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