I have two livedatas startedAt & finishedAt and want to use them in a transformation that depend on both these values...i tried combine them using mediatorliveData
fun <A, B> LiveData<A>.combine(other: LiveData<B>): PairLiveData<A, B> {
return PairLiveData(this, other)
}
class PairLiveData<A, B>(first: LiveData<A>, second: LiveData<B>) : MediatorLiveData<Pair<A?, B?>>() {
init {
addSource(first) { value = it to second.value }
addSource(second) { value = first.value to it }
}
}
and observe them
val automaticActivities = Transformations.map(startedAt.combine(finishedAt)) {
Log.v("checkindex",index.toString()+" "+it.first?.size+" "+it.second?.size)
}
but this doesn't work as expected as finishedAt returns null before it get its required value ,
debugged rsult :
V/checkindex: 0 1 null
V/checkindex: 0 1 1
will it be a good idea to use a transformation inside a transformation ? ex:
val automaticActivities = Transformations.map(startedAt) {
val finishedAt = Transformations.map(finishedAt){
}
}
Related
I have 3 editext and I have to multiply the numbers written in the first two, and make the result appear live on the third using Android Livedata.
viewModel.num1.observe(this,
Observer { newNum1-> binding.ediText1.text = newNum1.toString() }
viewModel.num2.observe(this,
Observer { newNum2-> binding.ediText2.text = newNum2.toString() }
viewModel.num3.observe(this,
Observer { newNum3-> binding.ediText3.text = newNum3.toString() }
I tried something like this, with 2 MutableLiveData and one MediatorLivedata, but i did something wrong because it didn't update live the third EditText. Could someone help me?
class MyViewModel : ViewModel() {
private var num1 = MutableLiveData<Int>();
private var num2 = MutableLiveData<Double>();
private var mun3 = MediatorLiveData<Double>();
num3.addSource(num1, this::onChanged);
num3.addSource(num2, this::onChanged);
private fun onChanged(x : Double) {
var a = num1.value
var b = num2.value
if (a== null)
a= 0;
if (b== null)
b= 0.0;
num3.setValue(a * b);
}
}
I'm using Kotlin but i accept any kind of code, even in java.
Thank you for your patience and help!
Best regards, Mark.
Please try something like that, but be aware of nullability. One of received values can be null
fun <A, B> LiveData<A>.combineWith(b: LiveData<B>): LiveData<Pair<A?, B?>> =
MediatorLiveData<Pair<A?, B?>>().apply {
var lastA: A? = this#combineWith.value
var lastB: B? = b.value
addSource(this#combineWith) {
lastA = it
value = Pair(lastA, lastB)
}
addSource(b) {
lastB = it
value = Pair(lastA, lastB)
}
}
viewModel.num1
.combineWith(viewModel.num2)
.observe(
this,
Observer { (first, second) ->
if (first != null && second != null) {
someEditText.text = (first * second).toString()
}
}
)
That might not be your literal code, because it's not compileable. You can't pass the same function to be used as the observer for either source, since the source types are different.
Your onChanged() function doesn't use the input parameter, so you can remove that and call it from a lambda you pass to each addSource call.
You can also simplify the content of your function by using Elvis operators.
private val num1 = MutableLiveData<Int>()
private val num2 = MutableLiveData<Double>()
private val num3 = MediatorLiveData<Double>().apply {
addSource(num1) { onChanged() }
addSource(num2) { onChanged() }
}
private fun onChanged() {
val a = num1.value ?: 0
val b = num2.value ?: 0.0
num3.value = a * b
}
I am using
Flowable.combineLatest(query,params) for listening query change and some param change
but now I want to introduce pagination and listen to offset changes , but the problem here is when query is changing I need to reset offset.
Wondering how can I achieve it with RxAndroid?
Basically we observe 3 or more objects (query, offset, connectionChange)
what I want to achieve is listen changes of any of the observables + when query is changed update the value for offset
To see where the value came from, you have to tag the values in some fashion, which requires per-source transformation. For example:
data class Tuple<T>(val value: T, val index: Long) { ... }
Flowable.defer {
var indices: Array<Long>(4) { 0 }
var latests: Array<Long>(4) { 0 }
Flowable.combineLatest(
source1.map { Tuple(it, indices[0]++) },
source2.map { Tuple(it, indices[1]++) },
source3.map { Tuple(it, indices[2]++) },
source4.map { Tuple(it, indices[3]++) },
{ tuple1, tuple2, tuple3, tuple4 ->
if (tuple1.index != latests[0]) {
// first source changed
}
if (tuple2.index != latests[1]) {
// second source changed
}
if (tuple3.index != latests[2]) {
// third source changed
}
if (tuple4.index != latests[3]) {
// fourth source changed
}
latests[0] = tuple1.index
latests[1] = tuple2.index
latests[2] = tuple3.index
latests[3] = tuple4.index
}
)
}
Maybe check something here
Pagination with Rx
https://github.com/kaushikgopal/RxJava-Android-Samples#14-pagination-with-rx-using-subjects
You can explicitly chain another call just after item has been emitted to the query flowable. Registering doAfterNext before Flowable is being register is probably easiest approach.
fun observePublishers(query: Flowable<List<String>>, connectionState: Flowable<Boolean>, offset: Flowable<Int>) {
val newQuery = query.doAfterNext {
index = 0
}
Flowable.combineLatest(newQuery, connectionState, offset) { queryResult, hasConnection, offsetValue ->
}.subscribe {
}
}
I'm doing validation on an EditText. I want the CharSequence to be invalid if it's empty or it doesn't begin with "https://". I'm also using RxBinding, specifically RxTextView. The problem is that when there is one character left, and I then delete it leaving no characters left in the the CharSequence the map operator doesn't fire off an emission. In other words I want my map operator to return false when the EditText is empty. I'm beginning to think this may not be possible the way I'm doing it. What would be an alternative?
Here is my Observable / Disposable:
val systemIdDisposable = RxTextView.textChanges(binding.etSystemId)
.skipInitialValue()
.map { charSeq ->
if (charSeq.isEmpty()) {
false
} else {
viewModel.isSystemIdValid(charSeq.toString())
}
}
.subscribe { isValid ->
if (!isValid) {
binding.systemIdTextInputLayout.isErrorEnabled = true
binding.systemIdTextInputLayout.error = viewModel.authErrorFields.value?.systemId
} else {
binding.systemIdTextInputLayout.isErrorEnabled = false
binding.systemIdTextInputLayout.error = viewModel.authErrorFields.value?.systemId
}
}
And here is a function in my ViewModel that I pass the CharSequence to for validation:
fun isSystemIdValid(systemId: String?): Boolean {
return if (systemId != null && systemId.isNotEmpty()) {
_authErrors.value?.systemId = null
true
} else {
_authErrors.value?.systemId =
getApplication<Application>().resources.getString(R.string.field_empty_error)
false
}
}
After sleeping on it, I figured it out.
I changed RxTextView.textChanges to RxTextView.textChangeEvents. This allowed me to query the CharSequence's text value (using text() method provided by textChangeEvents) even if it's empty. Due to some other changes (not really relevant to what I was asking in this question) I was also able to reduce some of the conditional code too. I'm just putting that out there in case someone comes across this and is curious about these changes. The takeaway is that you can get that empty emission using RxTextView.textChangeEvents.
Here is my new Observer:
val systemIdDisposable = RxTextView.textChangeEvents(binding.etSystemId)
.skipInitialValue()
.map { charSeq -> viewModel.isSystemIdValid(charSeq.text().toString()) }
.subscribe {
binding.systemIdTextInputLayout.error = viewModel.authErrors.value?.systemId
}
And here is my validation code from the ViewModel:
fun isSystemIdValid(systemId: String?): Boolean {
val auth = _authErrors.value
return if (systemId != null && systemId.isNotEmpty()) {
auth?.systemId = null
_authErrors.value = auth
true
} else {
auth?.systemId =
getApplication<Application>().resources.getString(R.string.field_empty_error)
_authErrors.value = auth
false
}
}
Lastly, if anyone is curious about how I'm using my LiveData / MutableLiveData objects; I create a private MutableLiveData object and only expose an immutable LiveData object that returns the values of the first object. I do this for better encapsulation / data hiding. Here is an example:
private val _authErrors: MutableLiveData<AuthErrorFields> by lazy {
MutableLiveData<AuthErrorFields>()
}
val authErrors: LiveData<AuthErrorFields>
get() { return _authErrors }
Hope this helps someone! 🤗
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.
is anyone facing this problem.
break or continue jump across class boundary kotlin
this problem appears when i am going to use break or continue. inside lambda with receiver i create 'letIn'
lambda with receiver code
fun letIn(componentName: String?, values: List<LifeService.Value?>?,
body: (String, List<LifeService.Value?>) -> Unit) {
if (!TextUtils.isEmpty(componentName) && (values != null && values.isNotEmpty())) {
body(componentName!!, values)
}
}
this sample code for it.
for (option in 0 until optionsSize) {
val component = optionsGroup?.options?.get(option)
component?.let {
with(component) {
letIn(presentation, values, { componentName, values ->
if (componentName == LifeComponentViewType.CHECKBOX) {
letIn(transformCheckBoxValues(optionsGroup), { data ->
dataSource?.push(componentName, ComponentDataCheckBoxCollection(name, data))
view.buildComponent(componentName)
// break or continue didnt work
})
} else {
dataSource?.push(componentName, ComponentDataCollection(name, values))
view.buildComponent(componentName)
}
})
}
}
}
because above code didnt work so i use imperative way.
for (option in 0 until optionsSize) {
val component = optionsGroup?.options?.get(option)
if (component != null) {
val presentation: String? = component.presentation
val values = component.values
if (!TextUtils.isEmpty(presentation)) {
if (presentation == LifeComponentViewType.CHECKBOX) {
val data = transformCheckBoxValues(optionsGroup)
if (data.isNotEmpty()) {
dataSource?.push(presentation, ComponentDataCheckBoxCollection(optionsGroup.name, data))
view.buildComponent(presentation)
return
}
} else {
dataSource?.push(presentation!!, ComponentDataCollection(component.name, values))
view.buildComponent(presentation!!)
}
} else {
return
}
}
}
does anyone have suggestions?
UPDATE
i've been fix this issue by inlining high order function.
(Other coding errors aside) You are seeing the error because inside your lambda, you cannot use break or continue to jump out of the lambda to the nearest loop. Instead, you can use a qualified return to jump out of the lambda to a label.
Referring to the language reference
The return-expression returns from the nearest enclosing function, i.e. foo. (Note that such non-local returns are supported only for lambda expressions passed to inline functions.) If we need to return from a lambda expression, we have to label it and qualify the return:
(Emphasis mine)
Your second example shows that you want your lambdas to do a non-local return from the enclosing function. Therefore, you do not need to qualify your return, but your function letIn must be declared inline (else you can only do a local, qualified return).
inline fun letIn(componentName: String?, values: List<LifeService.Value?>?,
body: (String, List<LifeService.Value?>) -> Unit) {
if (!TextUtils.isEmpty(componentName) && (values != null && values.isNotEmpty())) {
body(componentName!!, values)
}
}
... or if you want it to have receivers...
inline fun String?.letIn(values: List<LifeService.Value?>?,
body: String.(List<LifeService.Value?>) -> Unit) {
if (!TextUtils.isEmpty(this) && (values != null && values.isNotEmpty())) {
this!!.body(values)
}
}
When you declare letIn as inline, then you can place return in your lambdas without the compiler complaining. Your function would not need to be inline if your lambdas are only doing local returns, but it would need to have a qualified return (for example return#letIn).
Your first example would then look like this...
for (option in 0 until optionsSize) {
val component = optionsGroup?.options?.get(option)
component?.let {
with(component) {
presentation.letIn(values, { values ->
if (this == LifeComponentViewType.CHECKBOX) {
this.letIn(transformCheckBoxValues(optionsGroup), { data ->
dataSource?.push(this, ComponentDataCheckBoxCollection(this, data))
view.buildComponent(this)
return //returns from function
})
} else {
dataSource?.push(this, ComponentDataCollection(name, values))
view.buildComponent(this)
return //returns from function
}
})
}
}
}
Lastly, note that if you wanted to jump out of the lambda early, but continue an outer loop as in:
fun test1() {
val list = listOf("a", "b", "c")
val optionsSize = 2
for(i in 0..optionsSize) loop# {
println("calliing list.forEach")
list.forEach lit# {
if(it == "a") return#lit
if(it == "c") return#loop
println(it)
}
}
}
It won't work. Intelli-sense doesn't complain about it, but the compiler throws an internal error. But you can convert the outer loop to a lambda, and it does work...
fun test() {
val list = listOf("a", "b", "c")
val optionsSize = 2
(0..optionsSize).forEach() loop# {
println("calliing list.forEach")
list.forEach lit# {
if(it == "a") return#lit
if(it == "c") return#loop
println(it)
}
}
}
Again, this only works if the function to which the lambda is passed is declared inline (like forEach is declared inline).