Develop Reference

How to update object value in MutableList?

I have a MutableList in my Android project where i'm adding an object called Articolo, then when a new item is added to that list i need to check if one item with same ID exist and if it does i need to update it's quantity.
The issue is that i'm trying to use MutableList.find to find the object with the same ID and when i find it i'm simply add the quantity to existing quantity but instead it remains immutable.
Here is my Articolo.kt
data class Articolo(var barcode: String, var qta: Int) {
constructor() : this ("", 0)
}
And here is my function where i'm adding data to MutableList
private var articoli = mutableListOf<Articolo>()
private fun addBarcode(barcode: String, qta: Int) {
if (barcode.isEmpty()) {
txtBarcode.requestFocus()
return;
}
articoli.find{
it.barcode == barcode
}?.qta?.plus(qta) ?:
articoli.add(Articolo(barcode, qta))
}
So if i add the first object like barcode: 1111, qty: 1 and then another same object instead of having one element array with qty 2 i still have qty 1..

That's because .plus(Int) returns a new value. You're not changing the property.
Instead you should do:
fun addBarcode(barcode: String, qta: Int) {
val existant = articoli.find { it.barcode == barcode }
if (existant != null) existant.qta += qta
else articoli.add(Articolo(barcode, qta))
}

#VaiTon86 has the answer (you're not actually changing the value in the Articolo object) but really, you should probably be using a Map here anyway:
maximum one of each item
lookup by some value (barcode)
that's a map!
There's a few ways you could implement it, here's one:
val articoli = mutableMapOf<String, Articolo>()
private fun addBarcode(barcode: String, qta: Int) {
articoli.getOrPut(barcode) { Articolo(barcode, 0) }
.let { it.qta += qta }
}
So the getOrPut just adds a new zero-quantity Articolo entry if there isn't already one, and then you add qta to what's already there for that entry.

Kotlin - Get new index of item in shuffled list

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.

Unable to update pojo class in Kotlin

I am trying to update my pojo class on a particular click in Kotlin but it is giving me error :-
java.lang.stackoverflowerror: stack size 8mb
Here is my Pojo Class
class NavDrawerItem(var icon_normal: Int,var icon_notified: Int, var title: String, var isShowNotify: Boolean){
var title1: String = title
// get() = title // Calls the getter recursively
set(value)
{ title1 = value }
var image: Int = icon_normal
// get() = image
set(value)
{ image = value }
var image_notified: Int = icon_notified
// get() = image
set(value)
{ image_notified = value }
var notify: Boolean = isShowNotify
set(value) {
notify = value
}
}
I am updating my Pojo on the Item click of NavigationDrawer
override fun onItemClick(position: Int) {
mDrawerLayout?.closeDrawer(this!!.containerView!!)
position1 = position
for (i in navDrawerItems.indices) {
val item = navDrawerItems[i]
item.notify=(if (i == position) true else false)
navDrawerItems[i] = item
mAdapter?.notifyDataSetChanged()
}
}
Please help me!!!!

Your setters create infinite loop, which causes the StackOverflowError exceptions.
class NavDrawerItem(var icon_normal: Int,var icon_notified: Int, var title: String, var isShowNotify: Boolean){
var title1: String = title
// get() = title // Calls the getter recursively
set(value)
{ field = value }
var image: Int = icon_normal
// get() = image
set(value)
{ field = value }
var image_notified: Int = icon_notified
// get() = image
set(value)
{ field = value }
var notify: Boolean = isShowNotify
set(value) {
field = value
}
}
The above is setting the field, where your implementation was recursively setting the values.
Also, as ADM mentioned it's better to move the notifyDataSetChanged outside of the loop and not updating at each iteration.

Modify your class as a simple data class.
data class NavDrawerItem(var icon_normal: Int,var icon_notified: Int, var title: String, var isShowNotify: Boolean)
And
override fun onItemClick(position: Int) {
mDrawerLayout?.closeDrawer(this!!.containerView!!)
for (i in navDrawerItems.indices) {
val item = navDrawerItems[i]
item.notify=(i == position)
}
mAdapter?.notifyDataSetChanged()
}

It is always recommended to use data classes for defining pojos.
Because data classes are only made for storing data.
They provides many unique features over normal class in kotlin.
for example, you don't need to define setter and getters, they are automatically added to your data class.
In addition, your data class will automatically override some useful functions like equals, hashCode, toString, and etc.
defining data class is very easy.
data class Foo ( val title : String, val isHungry : Boolean ){
}

Sorting Strings that contains number in kotlin

I wanna sort some strings that contain numbers but after a sort, it becomes like this ["s1", "s10", "s11", ... ,"s2", "s21", "s22"]. after i search i fount this question with same problem. but in my example, I have mutableList<myModel>, and I must put all string in myModel.title for example into a mutable list and place into under code:
val sortData = reversedData.sortedBy {
//pattern.matcher(it.title).matches()
Collections.sort(it.title, object : Comparator<String> {
override fun compare(o1: String, o2: String): Int {
return extractInt(o1) - extractInt(o2)
}
fun extractInt(s: String): Int {
val num = s.replace("\\D".toRegex(), "")
// return 0 if no digits found
return if (num.isEmpty()) 0 else Integer.parseInt(num)
}
})
}
I have an error in .sortedBy and Collections.sort(it.title), may please help me to fix this.

you can use sortWith instead of sortBy
for example:
class Test(val title:String) {
override fun toString(): String {
return "$title"
}
}
val list = listOf<Test>(Test("s1"), Test("s101"),
Test("s131"), Test("s321"), Test("s23"), Test("s21"), Test("s22"))
val sortData = list.sortedWith( object : Comparator<Test> {
override fun compare(o1: Test, o2: Test): Int {
return extractInt(o1) - extractInt(o2)
}
fun extractInt(s: Test): Int {
val num = s.title.replace("\\D".toRegex(), "")
// return 0 if no digits found
return if (num.isEmpty()) 0 else Integer.parseInt(num)
}
})
will give output:
[s1, s21, s22, s23, s101, s131, s321]

A possible solution based on the data you posted:
sortedBy { "s(\\d+)".toRegex().matchEntire(it)?.groups?.get(1)?.value?.toInt() }
Of course I would move the regex out of the lambda, but it is a more concise answer this way.

A possible solution can be this:
reversedData.toObservable()
.sorted { o1, o2 ->
val pattern = Pattern.compile("\\d+")
val matcher = pattern.matcher(o1.title)
val matcher2 = pattern.matcher(o2.title)
if (matcher.find()) {
matcher2.find()
val o1Num = matcher.group(0).toInt()
val o2Num = matcher2.group(0).toInt()
return#sorted o1Num - o2Num
} else {
return#sorted o1.title?.compareTo(o2.title ?: "") ?: 0
}
}
.toList()
.subscribeBy(
onError = {
it
},
onSuccess = {
reversedData = it
}
)

As you state that you need a MutableList, but don't have one yet, you should use sortedBy or sortedWith (in case you want to work with a comparator) instead and you get just a (new) list out of your current one, e.g.:
val yourMutableSortedList = reversedData.sortedBy {
pattern.find(it)?.value?.toInt() ?: 0
}.toMutableList() // now calling toMutableList only because you said you require one... so why don't just sorting it into a new list and returning a mutable list afterwards?
You may want to take advantage of compareBy (or Javas Comparator.comparing) for sortedWith.
If you just want to sort an existing mutable list use sortWith (or Collections.sort):
reversedData.sortWith(compareBy {
pattern.find(it)?.value?.toInt() ?: 0
})
// or using Java imports:
Collections.sort(reversedData, Compatarator.comparingInt {
pattern.find(it)?.value?.toInt() ?: 0 // what would be the default for non-matching ones?
})
Of course you can also play around with other comparator helpers (e.g. mixing nulls last, or similar), e.g.:
reversedData.sortWith(nullsLast(compareBy {
pattern.find(it)?.value
}))
For the samples above I used the following Regex:
val pattern = """\d+""".toRegex()

I wrote a custom comparator for my JSON sorting. It can be adapted from bare String/Number/Null
fun getComparator(sortBy: String, desc: Boolean = false): Comparator<SearchResource.SearchResult> {
return Comparator { o1, o2 ->
val v1 = getCompValue(o1, sortBy)
val v2 = getCompValue(o2, sortBy)
(if (v1 is Float && v2 is Float) {
v1 - v2
} else if (v1 is String && v2 is String) {
v1.compareTo(v2).toFloat()
} else {
getCompDefault(v1) - getCompDefault(v2)
}).sign.toInt() * (if (desc) -1 else 1)
}
}
private fun getCompValue(o: SearchResource.SearchResult, sortBy: String): Any? {
val sorter = gson.fromJson<JsonObject>(gson.toJson(o))[sortBy]
try {
return sorter.asFloat
} catch (e: ClassCastException) {
try {
return sorter.asString
} catch (e: ClassCastException) {
return null
}
}
}
private fun getCompDefault(v: Any?): Float {
return if (v is Float) v else if (v is String) Float.POSITIVE_INFINITY else Float.NEGATIVE_INFINITY
}

Remove data from list while iterating kotlin

I am new to kotlin programming. What I want is that I want to remove a particular data from a list while iterating through it, but when I am doing that my app is crashing.
for ((pos, i) in listTotal!!.withIndex()) {
if (pos != 0 && pos != listTotal!!.size - 1) {
if (paymentsAndTagsModel.tagName == i.header) {
//listTotal!!.removeAt(pos)
listTotal!!.remove(i)
}
}
}
OR
for ((pos,i) in listTotal!!.listIterator().withIndex()){
if (i.header == paymentsAndTagsModel.tagName){
listTotal!!.listIterator(pos).remove()
}
}
The exception which I am getting
java.lang.IllegalStateException

use removeAll
pushList?.removeAll { TimeUnit.MILLISECONDS.toMinutes(
System.currentTimeMillis() - it.date) > THRESHOLD }

val numbers = mutableListOf(1,2,3,4,5,6)
val numberIterator = numbers.iterator()
while (numberIterator.hasNext()) {
val integer = numberIterator.next()
if (integer < 3) {
numberIterator.remove()
}
}

It's forbidden to modify a collection through its interface while iterating over it. The only way to mutate the collection contents is to use Iterator.remove.
However using Iterators can be unwieldy and in vast majority of cases it's better to treat the collections as immutable which Kotlin encourages. You can use a filter to create a new collections like so:
listTotal = listTotal.filterIndexed { ix, element ->
ix != 0 && ix != listTotal.lastIndex && element.header == paymentsAndTagsModel.tagName
}

The answer by miensol seems perfect.
However, I don't understand the context for using the withIndex function or filteredIndex. You can use the filter function just by itself.
You don't need access to the index the list is at, if you're using
lists.
Also, I'd strongly recommend working with a data class if you already aren't. Your code would look something like this
Data Class
data class Event(
var eventCode : String,
var header : String
)
Filtering Logic
fun main(args:Array<String>){
val eventList : MutableList<Event> = mutableListOf(
Event(eventCode = "123",header = "One"),
Event(eventCode = "456",header = "Two"),
Event(eventCode = "789",header = "Three")
)
val filteredList = eventList.filter { !it.header.equals("Two") }
}

The following code works for me:
val iterator = listTotal.iterator()
for(i in iterator){
if(i.haer== paymentsAndTagsModel.tagName){
iterator.remove()
}
}
You can also read this article.

People didn't break iteration in previous posts dont know why. It can be simple but also with extensions and also for Map:
fun <T> MutableCollection<T>.removeFirst(filter: (T) -> Boolean) =
iterator().removeIf(filter)
fun <K, V> MutableMap<K, V>.removeFirst(filter: (K, V) -> Boolean) =
iterator().removeIf { filter(it.key, it.value) }
fun <T> MutableIterator<T>.removeFirst(filter: (T) -> Boolean): Boolean {
for (item in this) if (filter.invoke(item)) {
remove()
return true
}
return false
}

Use a while loop, here is the kotlin extension function:
fun <E> MutableList<E>.removeIfMatch(isMatchConsumer: (existingItem: E) -> Boolean) {
var index = 0
var lastIndex = this.size -1
while(index <= lastIndex && lastIndex >= 0){
when {
isMatchConsumer.invoke(this[index]) -> {
this.removeAt(index)
lastIndex-- // max is decreased by 1
}
else -> index++ // only increment if we do not remove
}
}
}

Typically you can use:
yourMutableCollection.removeIf { someLogic == true }
However, I'm working with an Android app that must support APIs older than 24.
In this case removeIf can't be used.
Here's a solution that is nearly identical to that implemented in Kotlin Collections that doesn't rely on Predicate.test - which is why API 24+ is required in the first place
//This function is in Kotlin Collections but only for Android API 24+
fun <E> MutableCollection<E>.removeIff(filter: (E) -> Boolean): Boolean {
var removed = false
val iterator: MutableIterator<E> = this.iterator()
while (iterator.hasNext()) {
val value = iterator.next()
if (filter.invoke(value)) {
iterator.remove()
removed = true
}
}
return removed
}

Another solution that will suit small collections. For example set of listeners in some controller.
inline fun <T> MutableCollection<T>.forEachSafe(action: (T) -> Unit) {
val listCopy = ArrayList<T>(this)
for (element: T in listCopy) {
if (this.contains(element)) {
action(element)
}
}
}
It makes sure that elements of collection can be removed safely even from outside code.