I am learning to build a simple android app with android studio and i created a function to find the id of some values. While writing this function I thought using when statement (Kotlin) but a sadly had to repeat it. Is there a way to assign the result of a when statement to multiple variables at the same time? In other language I would just have returned a list which I would have disassembled but I can't find a way to do it in Kotlin. It's not really big problem but I like optimizing my code.
// my Kotlin function
// setting a specific state
private fun setState(num: Int) {
Log.v(TAG, num.toString())
// get the correct image id
val imageId: Int? = when (num) {
0 -> R.drawable.lemon_restart
1 -> R.drawable.lemon_tree
2 -> R.drawable.lemon_squeeze
3 -> R.drawable.lemon_drink
else -> null
}
// get the correct text to show
val txtId: Int? = when (num) {
0 -> R.string.txt_state_0
1 -> R.string.txt_state_1
2 -> R.string.txt_state_2
3 -> R.string.txt_state_3
else -> null
}
// get the correct content description for accessibility
val contentDescriptionId: Int? = when (num) {
0 -> R.string.lemon_restart_description
1 -> R.string.lemon_tree_description
2 -> R.string.lemon_squeeze_description
3 -> R.string.lemon_drink_description
else -> null
}
// setting the new stuff
val imView: ImageView = findViewById(R.id.imageState)
val txtView: TextView = findViewById(R.id.textOrder)
txtView.text = getString(txtId!!)
imView.setImageResource(imageId!!)
imView.contentDescription = getString(contentDescriptionId!!)
}
feel free to optimize it as much as possible
You can return Triple or your own data class from when, and then destructure it:
val (imageId, txtId, contentDescriptionId) = when (num) {
0 -> Triple(R.drawable.lemon_restart, R.string.txt_state_0, R.string.lemon_restart_description)
...
else -> Triple(null, null, null)
}
Since every field is constant and states are fixed. you can make the states as constant. to decouple code little bit you can create a separate class to return the values for particular state. below is an Example :
class StateHandle private constructor(imageId: Int?, txtId: Int?, contentDescriptionId: Int?) {
companion object {
private val imageIds = arrayOf(
R.drawable.lemon_restart,
R.drawable.lemon_tree,
R.drawable.lemon_squeeze,
R.drawable.lemon_drink
)
private val txtIds = arrayOf(
R.string.txt_state_0,
R.string.txt_state_1,
R.string.txt_state_2,
R.string.txt_state_3
)
private val contentIds = arrayOf(
R.string.lemon_restart_description,
R.string.lemon_tree_description,
R.string.lemon_squeeze_description,
R.string.lemon_drink_description
)
#JvmStatic
fun getStateFor(num: Int): StateHandle {
return StateHandle(
imageIds.getOrNull(num), txtIds.getOrNull(num),
imageIds.getOrNull(num)
)
}
}
}
Its not perfect but it is a bit more reusable . just call #getStateFor and use the StateHandle object .
Related
For example, I load data into a List, it`s wrapped by MutableStateFlow, and I collect these as State in UI Component.
The trouble is, when I change an item in the MutableStateFlow<List>, such as modifying attribute, but don`t add or delete, the UI will not change.
So how can I change the UI when I modify an item of the MutableStateFlow?
These are codes:
ViewModel:
data class TestBean(val id: Int, var name: String)
class VM: ViewModel() {
val testList = MutableStateFlow<List<TestBean>>(emptyList())
fun createTestData() {
val result = mutableListOf<TestBean>()
(0 .. 10).forEach {
result.add(TestBean(it, it.toString()))
}
testList.value = result
}
fun changeTestData(index: Int) {
// first way to change data
testList.value[index].name = System.currentTimeMillis().toString()
// second way to change data
val p = testList.value[index]
p.name = System.currentTimeMillis().toString()
val tmplist = testList.value.toMutableList()
tmplist[index].name = p.name
testList.update { tmplist }
}
}
UI:
setContent {
LaunchedEffect(key1 = Unit) {
vm.createTestData()
}
Column {
vm.testList.collectAsState().value.forEachIndexed { index, it ->
Text(text = it.name, modifier = Modifier.padding(16.dp).clickable {
vm.changeTestData(index)
Log.d("TAG", "click： ${index}")
})
}
}
}
Both Flow and Compose mutable state cannot track changes made inside of containing objects.
But you can replace an object with an updated object. data class is a nice tool to be used, which will provide you all copy out of the box, but you should emit using var and only use val for your fields to avoid mistakes.
Check out Why is immutability important in functional programming?
testList.value[index] = testList.value[index].copy(name = System.currentTimeMillis().toString())
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")
}
}
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!
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
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!
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.
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)
}
}
}
}
}
...
The fragment I am coding right now is supposed to give the user a calendaric overview of his meal planning schedule. So via date picker, he can choose a time period and the program will show the user which recipes he has chosen for the chosen weekdays.
So I build a nested RecyclerView with the weekdays as parent layer and corresponding recipes as a child layer. The data class for the weekday layer looks like this :
data class Weekday (
val weekday : String,
val listWithRecipes : List<Recipe>?
)
The class for the Recipe entity looks like this:
#Entity(tableName = "Recipe")
#Parcelize
data class Recipe(
#PrimaryKey var recipeName : String,
var description : String?,
var serving : Int,
var preparationTime : Int?
) : Parcelable
The Adapter for the top Recycler View like this :
class MealPlanAdapter(private var mealplan: List<Weekday>) :
RecyclerView.Adapter<MealPlanAdapter.MealPlanViewHolder>(), RecipeAdapter.OnItemClickListener {
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): MealPlanViewHolder {
return MealPlanViewHolder(
DailyMealplanItemBinding.inflate(
LayoutInflater.from(parent.context),
parent,
false
)
)
}
override fun getItemCount() = mealplan.size
override fun onBindViewHolder(holder: MealPlanViewHolder, position: Int) {
val weekday = mealplan[position]
val recipeAdapter = RecipeAdapter(this)
recipeAdapter.submitList(weekday?.listWithRecipes)
holder.dayOfWeek.text = weekday.weekday
val recipeLayoutManager = LinearLayoutManager(holder.recyclerView.context,RecyclerView.VERTICAL, false)
recipeLayoutManager.initialPrefetchItemCount = 4
holder.recyclerView.apply{
layoutManager = recipeLayoutManager
adapter = recipeAdapter
}
}
fun setSchedule(mealplan : List <Weekday>){
this.mealplan = mealplan
notifyDataSetChanged()
}
inner class MealPlanViewHolder(val binding: DailyMealplanItemBinding) :
RecyclerView.ViewHolder(binding.root) {
val recyclerView: RecyclerView = binding.rvRecyclerView
val dayOfWeek: TextView = binding.tvDayOfWeek
}
override fun onItemClick(recipe: Recipe) {
TODO("Not yet implemented")
}
}
Whenever the user changes the time period, the setScheduled() method in the adapter gets called in the fragment.
materialDatePickerStartDate.addOnPositiveButtonClickListener(
MaterialPickerOnPositiveButtonClickListener<Any?> { selection ->
_binding.viewmodel!!.startDateInUTCFormat = selection as Long
_binding.tvStartDate.setText(materialDatePickerStartDate.headerText)
adapter.setSchedule(
_binding.viewmodel!!.returnListWithWeekDaysAndCorrespondingRecipes(
_binding.viewmodel!!.startDateInUTCFormat,
_binding.viewmodel!!.endDateInUTCFormat
)
)
}
)
The viewmodel looks like this :
#HiltViewModel
class MealplanViewModel #Inject constructor(
val mealPlanRepository: MealPlanRepository
) : ViewModel() {
private lateinit var _binding: FragmentMealPlanBinding
var startDateInUTCFormat: Long = System.currentTimeMillis()
var endDateInUTCFormat: Long = System.currentTimeMillis()
fun returnListWithWeekDaysAndCorrespondingRecipes(
startDate: Long,
endDate: Long
): ArrayList<Weekday> {
var startDate = Date(startDateInUTCFormat)
var endDate = Date(endDateInUTCFormat)
var startDateCalendar = dateToCalendar(startDate)
var endDateCalendar = dateToCalendar(endDate)
val calendarDays = createListWithCalendarDates(startDateCalendar, endDateCalendar)
return createListWithWeekDaysAndCorrespondingRecipes(calendarDays)
}
fun dateToCalendar(date: Date): Calendar {
var calInstance = Calendar.getInstance()
calInstance.setTime(date)
return calInstance
}
fun createListWithCalendarDates(
startDateCalendar: Calendar,
endDateCalendar: Calendar
): ArrayList<Calendar> {
var listWithCalendarDates = arrayListOf<Calendar>()
while (startDateCalendar <= endDateCalendar) {
listWithCalendarDates.add(startDateCalendar.clone() as Calendar)
startDateCalendar.add(Calendar.DATE, 1)
}
return listWithCalendarDates
}
fun createListWithWeekDaysAndCorrespondingRecipes(calendarDays: ArrayList<Calendar>): ArrayList<Weekday> {
var dayOfWeekAsString: String
var listWithDaysOfWeeksAndRecipes = arrayListOf<Weekday>()
var flattenedListWithRecipes: List<Recipe>?
for (i in 0 until calendarDays.size) {
var dayOfWeekAsInt = calendarDays[i].get(Calendar.DAY_OF_WEEK)
dayOfWeekAsString = when (dayOfWeekAsInt) {
1 -> "Sunday"
2 -> "Monday"
3 -> "Tuesday"
4 -> "Wednesday"
5 -> "Thursday"
6 -> "Friday"
else -> "Saturday"
}
var calendarDateInString =
transformCalendarDateIntoRequiredStringFormat(calendarDays[i])
var listWithDateAndCorrespondingRecipes: List<MealplanScheduleWithRecipes> =
listOf()
var liveDatalistWithDateAndCorrespondingRecipes =
mealPlanRepository.getMealplanScheduleWithRecipes(calendarDateInString)
liveDatalistWithDateAndCorrespondingRecipes.observeForever() { list ->
listWithDateAndCorrespondingRecipes = list
var listWithRecipes = listWithDateAndCorrespondingRecipes?.map { it.recipes }
flattenedListWithRecipes = listWithRecipes?.flatten()
var wochentag = dayOfWeekAsString
listWithDaysOfWeeksAndRecipes.add(Weekday(dayOfWeekAsString, flattenedListWithRecipes))
}
}
return listWithDaysOfWeeksAndRecipes
}
fun transformCalendarDateIntoRequiredStringFormat(calendarDate: Calendar): String {
var year = calendarDate.get(Calendar.YEAR)
var month = transformCalendarMonthFormatToCorrectMonth(calendarDate)
var day = calendarDate.get(Calendar.DAY_OF_MONTH)
return "$day" + "$month" + "$year"
}
fun transformCalendarMonthFormatToCorrectMonth(calendarDate: Calendar): String {
var monthCalendarFormat = calendarDate.get(Calendar.MONTH)
var monthCorrectFormat = when (monthCalendarFormat) {
0 -> "1"
1 -> "2"
2 -> "3"
3 -> "4"
4 -> "5"
5 -> "6"
6 -> "7"
7 -> "8"
8 -> "9"
9 -> "10"
10 -> "11"
else -> "12"
}
return monthCorrectFormat
}
fun datesAreReasonable(startDate: Long, endDate: Long): Boolean {
return (startDate <= endDate)
}
}
My problem is the list that is passed to the RecyclerView Adapter consists of Weekday objects, which consist of the name of the weekday and the corresponding recipes (see data class "weekday" on top).
In the method "createListWithWeekDaysAndCorrespondingRecipes" in the viewmodel I create this list in a for loop that gets all weekdays between given Dates and their corresponding recipes. However, the recipes are LiveData fetched asynchronously via Room database query while the names of the weekdays are derived synchronously in the main thread. At the end however when I create the Weekday object
(see listWithDaysOfWeeksAndRecipes.add(Weekday(dayOfWeekAsString, flattenedListWithRecipes) at the end of the for loop) I need them together at the same time. I haven't found a way how I can coordinate this successfully. At the moment the logics for adding the object to the list is in the asynchronous "observeForever" block.
See here:
liveDatalistWithDateAndCorrespondingRecipes.observeForever() { list ->
listWithDateAndCorrespondingRecipes = list
var listWithRecipes = listWithDateAndCorrespondingRecipes?.map { it.recipes }
flattenedListWithRecipes = listWithRecipes?.flatten()
var wochentag = dayOfWeekAsString
listWithDaysOfWeeksAndRecipes.add(Weekday(dayOfWeekAsString, flattenedListWithRecipes))
}
This creates wrong results, probably because the coordination between main thread and the observer thread doesn't work.
If I however take the logics of adding out of the observer block, the list with recipes will give me null, because of the asynchronous character of the query.
I know that I described the problem very badly. Maybe still someone got a grasp of it and can help?
You should try to avoid using observeForever, I expect you are using this inside a fragment or an activity which actually has a lifecyclescope that your observer can use.
Your observer should look something like this
liveDataList.observe(viewLifecycleOwner, { list ->
// The way I do it at the moment I just set the recyclerViews adapter and layoutManager here
// This is not the best way to do it, so please keep that in mind
recyclerView.apply {
adapter = MyAdapter(list)
layoutManager = LinearLayoutManager(requireContext())
}
})
// Or if used inside an activity
liveDataList.observe(this, {})
This way your observer will be attached to your lifecycle and "die" together with your view. Whenever that list changes, you will show all entities in the recyclerView. HOWEVER, when you use an Array together with LiveData the LiveData object never "updates" when you just add something to that value, since the array only is a memory reference to the start of the array.
To counter this whenever you add something to your array you need to refresh the LiveData object in order to trigger an update and all observers.
myLiveDataObject.value.add(someOtherObject)
myLiveDataObject.value = myLiveDataObject.value
myLiveDataObject.value = myLiveDataObject.value triggers all observers that there has been a change, annoying I know
If you use it inside a viewHolder or adapter simply pass the lifecycle along with the list
I am also quite new to kotlin, keep that in mind and I guarantee you there is a better way to do this, but hope it helps
I have a multiple choice quiz with 4 choices per answer. In the ArrayList with the questions and choices, the correct answer is set to the index of the correct option. I want to shuffle the choices but am not sure how to identify the new index of the correct answer. Any thoughts?
Question object
object ConstantsAnalysis {
const val TOTAL_CORRECT: String = "total_correct"
const val TOTAL_OPP: String = "total_opp"
fun getQuestions3(): ArrayList<Questions3> {
val questionList = ArrayList<Questions3>()
val q1 = Questions3(1, null,
"On a graph, the horizontal line along which data are plotted is the _____",
"y axis", "x axis", "origin", "quadrant", 2, R.string.Jones_1995, null)
questionList.addAll(listOf(q1))
questionList.shuffle()
return questionList
}
}
Data class
data class Questions3(
val id: Int, val image: Int?, val question: String, val option1: String, val option2: String,
val option3: String, val option4: String, val correctAnswer: Int, val dialogBox: Int?, val dialogBox2: Int?)
Shuffle choices
val ansorder = arrayOf(question.option1, question.option2, question.option3, question.option4)
ansorder.shuffle()
radio_button1.text = ansorder[0]
radio_button2.text = ansorder[1]
radio_button3.text = ansorder[2]
radio_button4.text = ansorder[3]
Check answer choice
if (questions3!!.correctAnswer != mSelectedOptionPosition) {
//do x
}
Edit (Since correct answer is a string and the index changes after shuffling, answerView(questions3.correctAnswer, R.drawable.correct_option_border.
class QuestionsActivityAnalysis : AppCompatActivity(), View.OnClickListener {
private var mCurrentPosition:Int = 1
private var mQuestionsList:ArrayList<Questions3>? = null
private var mSelectedOptionPosition:Int = 0
private var mCorrectAnswers: Int = 0
private var mSelectedOptionText: String? = null
private fun shuffle() {
val question = mQuestionsList!![mCurrentPosition - 1]
val ansorder = arrayOf(question.option1, question.option2, question.option3, question.option4)
ansorder.shuffle()
radio_button1.text = ansorder[0]
radio_button2.text = ansorder[1]
radio_button3.text = ansorder[2]
radio_button4.text = ansorder[3]
}
override fun onClick(v: View?) {
when(v?.id){
R.id.radio_button1 -> { selectedOptionView(radio_button1, 1)
mSelectedOptionText = radio_button1.text as String?
}
R.id.radio_button2 -> { selectedOptionView(radio_button2, 2)
mSelectedOptionText = radio_button2.text as String?
}
R.id.radio_button3 -> { selectedOptionView(radio_button3, 3)
mSelectedOptionText = radio_button3.text as String?
}
R.id.radio_button4 -> { selectedOptionView(radio_button4, 4)
mSelectedOptionText = radio_button4.text as String?
}
R.id.btn_submit -> {
val questions3 = mQuestionsList?.get(mCurrentPosition - 1)
if (questions3!!.correctAnswer != mSelectedOptionText) {
} else {
mCorrectAnswers++
}
answerView(questions3.correctAnswer, R.drawable.correct_option_border)
private fun answerView(answer: Int, drawableView: Int) {
when(answer){
1 -> {
radio_button1.background = ContextCompat.getDrawable(this, drawableView)
}
2 -> {
radio_button2.background = ContextCompat.getDrawable(this, drawableView)
}
3 -> {
radio_button3.background = ContextCompat.getDrawable(this, drawableView)
}
4 -> {
radio_button4.background = ContextCompat.getDrawable(this, drawableView)
}
}
}
I would really recommend just creating a data class like this:
data class QuestionOption(val question:String, val isCorrect = false)
Afterwards you can shuffle any way you like and just check if the selected QuestionOption has isCorrect set to true. You get a bunch of benefits and the logic gets simpler.
Edit:
To make it easier to declare questions this way:
In general if you add questions in your code you want only as much necessary code as required. For this you can either declare a good constructor or a function that basically maps your values to a constructor. In your case I'd say
data class Questions3(
val id: Int, val question: String, val option1: String, val option2: String,
val option3: String, val correctOption: String, val image: Int?=null,val dialogBox1: Int?=null,val dialogBox2: Int?=null)
(notice how the optional parameters are last, you don't need to specify them as well thanks to them beeing null by default)
Makes sense, in theory you could also (not too clean but easy) just shuffle option 1-3 & correctOption and then just compare if the correctOption String matches the selected String.
Otherwise as I said, you can always create logic for mapping stuff. Here you can either map from Constructor to another Constructor, same with Functions that return a finished Object.
I got this mutablelist:
[Videos(id=4, yt_id=yRPUkDjwr1A, title=test4, likes=0, kat=pranks, ilike=false), Videos(id=3, yt_id=WkyUU9ZDUto, title=test3, likes=0, kat=pranks, ilike=false), Videos(id=2, yt_id=B_X9OQqtduE, title=test2, likes=0, kat=animals, ilike=false), Videos(id=1, yt_id=ywaKlGNiv80, title=test1, likes=0, kat=animals, ilike=false)]
How can I change ilike to true where id is 2
This is what I've tried:
for (i in 0 until vids!!.size) {
Log.d("lets", vids!!.get(i).title)
if(vids!!.get(i).id == 2){
vids!!.get(i).ilike = true
}
}
You can use find function to find the element with id = 2 and change its property:
vids?.find { it.id == 2 }?.iLike = true
Note: it is a good practice to use question mark if the property is nullable and you unsure whether it is null or not.
If you expect few items (maybe 1 or 2?) to be affected,
you can filter the list and then change iLike of the filtered items:
vids!!.filter { it.id == 2 }.forEach { it.iLike = true }
Try this, I'm assuming your Videos structure is a data class defined somewhat like so. data class Videos(val id: Int, val yt_id: String, val title: String, val likes: Int, val kat: String, val ilike: Boolean)
list.forEachIndexed { index, video ->
video.takeIf { it.id == 2}?.let {
list[index] = it.copy(ilike = true)
}
}
I had to change several properties and I had a need to hold the changed object. Therefore following approach worked better for me:
//First, find the position of the video in the list
val videoPosition= list.indexOfFirst {
it.id == 2
}
//Now get your video by position and make changes
val updatedVideo = list[videoPosition].apply {
//Make all changes you need here
ilike = true
//...
}
//Finally, replace updated video into your list.
list[videoPosition] = updatedVideo
Use set to replace the object if you don't want to use predicates or iteration
Eg.
val video = (...,read = true) //or however you are getting the current model
val updatedVideo = video
updatedVideo.read = true
vids[vids.indexOf(video)] = updatedVideo