Declaration-site variance may cause ClassCastException Kotlin introduces Declaration-site variance described at here. The out/in keywords for generic parameters may cause ClassCastException in some case. My program is shown below. fun main(args: Array) { var l: List = mutableListOf("string") demo(l) println("======") for (s in l) { println(s) } } fun demo(strs: List) { val objects: List = strs //...

Using Kotlin WHEN clause for &amp;lt;, &amp;lt;=, &amp;gt;=, &amp;gt; comparisons I'm trying to use the WHEN clause with a > or 0 -> doSomethingWhenPositive() 0 -> doSomethingWhenZero() < 0 -> doSomethingWhenNegative() } I tried to find an unbounded range comparison, but couldn't make this work either? Is it possible to write this as an unbounded range? // trying to get an unbounded range - doesn't compile when (foo) { in 1.. -> doSomethingWhenPositive() else -> doSomethingElse() } You can put the whole expression in the second part, which is OK but...

Swap Function in Kotlin is there any better way to write generic swap function in kotlin other than java way described in How to write a basic swap function in Java. Is there any kotlin language feature which can make generic swap function more concise and intuitive?

How to reverse a Map in Kotlin? I am trying to reverse a Map in Kotlin. So far, I have come up with: mapOf("foo" to 42) .toList() .map { (k, v) -> v to k } .toMap() Is there any better way of doing this without using a middleman(middlelist)?

How to dynamically scale debounce of burst emission stream? I've got a buffered stream, waiting for a predetermined amount of silence time, before publishing a list of elements that have been buffered: INTEGERS .share() .buffer(INTEGERS.debounce(DEBOUNCE_TIME,TimeUnit.MILLISECONDS,scheduler)) .map { durations -> ... } I'd like to make DEBOUNCE_TIME dynamically adjust depending on the average of the buffered items, but I'm having a hard time figuring out how to achieve this.

MVP Presenter not injected correctly I am learning Kotlin and Dagger 2 simultaneously by attempting to convert some of Mindorks advanced MVP sample to Kotlin but am having Dagger2 compile issues. I am swimming in classes here but am very close! Don't mind the untidiness, I intend to comb over each class once it compiles. If something is missing please let me know. The error comes down to my presenter class not being...

Using a Flux instead of a for loop, any benefits? I am trying to get my head around reactive programming so I would like to ask if there is any benefit to using a Flux here: override fun notifyObserversOnMessage(message: Message) { Flux.fromStream(observers.stream()) .map { observer -> Mono.just(observer.reactOnMessage(message)) } .subscribe() } instead of: override fun notifyObserversOnMessage(message: Message) { for (observer in observers) {...

Why can't dagger process these kotlin generics? I'm having some weird kotlin generic issues with Dagger that I kinda fixed but the solution isn't sound. Here's the dagger classes: @Module class P5Module { @Provides fun pool(): RecyclerView.RecycledViewPool = RecyclerView.RecycledViewPool() @Provides fun adapters(fusion: P5FusionAdapter, personas: P5ListAdapter, skills: P5SkillsAdapter, info: InfoAdapter) : List = listOf(fusion, personas, skills, info) } @ActivityScope @Subcomponent(modules =...

Confused about kotlin / android I am new to android. I am confused what to learn android studio or kotlin. I don't know anything about android development.

How to get and display user input in Kotlin in Android Studio? Alright, how can I go about getting a user input in Kotlin and having that displayed in a textview? Basically, this JS code translated to Kotlin in Android Studio: function myFunction() { var choices = [ document.getElementById('input1').value, document.getElementById('input2').value, document.getElementById('input3').value ]; var random = Math.floor(Math.random()*choices.length); document.getElementById("result").innerHTML = choices[random]; } Thanks a bunch!

Kotlin with Map ( Marker Not showing) Hello Below is the code for google map in kotlin but in these code my mapasync is not getting call.. var mapFragment : SupportMapFragment?=null mapFragment= fragmentManager.findFragmentById(R.id.map) as SupportMapFragment? mapFragment?.getMapAsync { val sydney = LatLng(22.30, 73.20) mMap!!.addMarker(MarkerOptions().position(sydney).title("Marker in Sydney")) mMap!!.moveCamera(CameraUpdateFactory.newLatLng(sydney))...

Kotlin || How to distinguish the view id from onClick() like switch statement in Andorid? As we know in Android we are using the switch statement to distinct the view like below, We used to implement View.OnClickListener to get onClick interface method to perform any task @Override public void onClick(View view) { switch (view.getId()) { case R.id.imgBack: ///DO SOME THING HERE break; case R.id.btnSubmit: ///DO SOME THING HERE break; } } Same thing i am using in...

What is legitimate way to get annotations of a pure Kotlin property, are they always missing? I'm trying to get annotations from Kotlin data class package some.meaningless.package.name import kotlin.reflect.full.memberProperties annotation class MyAnnotation() @MyAnnotation data class TestDto(@MyAnnotation val answer: Int = 42) fun main(args: Array) { TestDto::class.memberProperties.forEach { p -> println(p.annotations) } println(TestDto::class.annotations) } I need to process class annotation to make a custom name serialization of GSON however no matter how I declare...

Disable a button Hello I would like to do this : I have two EditText and one button and I would like to disable the button if one of the EditText is empty. To do this I try this : if(editText1!!.getText().length == 0 || editText2!!.getText().length == 0 ){ button1!!.setEnabled(false) } The problem is my button is everytime disable... and I would when the two EditText are not empty I can click on the button... How can I do this ? Thank you !

Confused about Null Safety in Kotlin I am new to Kotlin and have read more than one time about Null Safety in Kotlin but I am really confused and do not understand clearly. Can anyone helps me answer questions below: What does ! character in fun getString(key: String!) mean? Is the names of operators below correct: ?.: Safe call operator ?:: Elvis operator !!: Sure operator What does differences between ?: operator and ?.let?...

Broadcast Reciver in kotlin how to use register and create a Broadcast Receiver in android in Kotlin. Any advice.... In java you can create it by declaring it as an Broadcast Receiver.But in Kotlin there is no Broadcast Receiver function...well if it is there then I am not able to find it or how to use it.

Do I learn Kotlin or Java for Android? As Fresher? I am new and want to learn android apps development. But which language to choose Java or Kotlin? Kotlin is an official language of Android but doesn't have enough resource to learn. And also i heard Java have some issues like: lamda and so on. Should i go with Java or Kotlin?

Cannot unmarshal a collection of xml objects using JAXB and Kotlin I am trying to deserialize/unmarshal XML that contains a collection of Person elements wrapped in People tag. I am attempting to deserialize this XML in Kotlin using JAXB. Everything compiles and runs without errors but the people collection in my class is always empty. How do I unmarshal this collection? import java.io.StringReader import javax.xml.bind.JAXB import javax.xml.bind.annotation.XmlAccessType import javax.xml.bind.annotation.XmlAccessorType import...

Kotlin internal classes in Java visible publicly I am developing an Android crypto library in Kotlin. I have a couple of internal classes which become publicly visible in a Java app. Found this in documentations. internal declarations become public in Java. Members of internal classes go through name mangling, to make it harder to accidentally use them from...

What's the recommended way to deal with Singletons cleanup in Android (Kotlin)? I have been having some weird issues in my Android app when closing it via back key and reentering, and found they are happening because variables in 2 Singleton classes I have are never re-initializing (The issue doesn't happen if manually killing the app from task manager). Even after I call finish explicitly on Main activity onBackPressed and I can see onDestroy is called, the Singletons are still in memory. I decided to do manual cleanup of these Singletons before destroying my...

Reference enum instance directly without class in Kotlin In Kotlin, I'm unable to reference the instances of an enum directly: enum class E { A, B } What I want to do: val e = A What I can do: val e = E.A Is this possible?

How to draw lines using drawLine() I am new to android. I am trying to draw a line using drawLine(). The line is not appearing, can someone debug this code? fun LinePlacer(btn: Button?, callInt,cPlayerInt?){ var xStart=btn!!.getTop().toFloat() var yStart=btn!!.getLeft().toFloat() var xStop=xStart+100 var yStop=yStart+100 var paint=Paint() paint.setColor(Color.RED) Draw(xStart,yStart,yStop,xStop,paint) } fun Draw(xStartFloat,yStartFloat,yStopFloat,xStopFloat,paint: Paint){ var...

Functional APIs for collections confused &amp;quot;all&amp;quot; function,can you explain it? I'm trying an example in kotlin,like: fun test(){ val harfler = listOf("a","b",'c','d') println(harfler.all { (it.javaClass == String::class.java || it.javaClass == Char::class.java) }) } List contains Char or String but all function in this expression returns false,Why return false? Can anybody explain it?

Kotlin start Application crash my application is built with kotlin,here is my build.gradle file: compile "org.jetbrains.kotlinkotlin stdlib$kotlin_version" and my workspace's build.gradle file: ext.kotlin_version = '1.1.3-2' ext.kotlin_plugin_version = '1.1.1' dependencies { classpath "io.realmrealm gradle plugin3.4.0" classpath "org.jetbrains.kotlinkotlin gradle plugin$kotlin_plugin_version" } in my project,I already use java8 with jack, so the gradle-plugin version can only be 1.1.1 when I start my...

Outdated Kotlin Runtime I got this message when i wanted to update the kotlin runtime: Your version of Kotlin runtime in 'kotlin-stdlib-1.1.2-4' library is 1.1.2-4, while plugin version is 1.1.3-release-Studio 3.0-2. Runtime library should be updated to avoid compatibility problems. Some of codes segment which is exist in the file build.gradle ext.kotlin_version = '1.1.2-4' classpath 'com.android.tools.buildG3.0.0-alpha8' Can anyone help me to solve this issue? Thanks in advance..

Gradle. Kotlin - is it possible to create dynamic (&amp;quot;on fly&amp;quot;) tasks? I'm an android developer. And as result write build by Gradle. Many tasks I write on Gradle DSL on Groovy. Sometimes I need to create Gradle tasks dynamically ("on fly"). Here example: task installDebugFlavors() { android.applicationVariants.all { v -> if (v.name.endsWith('Debug')) { String name = v.name.capitalize() dependsOn "install$name" } } } This task generate new tasks with all flavors combinations. As result Gradle script is very...

Difference between adding instance and caching What's the difference between those two codes? Both of them produce the same result. (Warning: Kotlin code) With caching: val cachingContainer = DefaultPicoContainer(OptInCaching().wrap(ConstructorInjection())) cachingContainer.`as`(Characteristics.CACHE).addComponent(Cookie::class.java, Cookie::class.java, *Parameter.ZERO) val cookie1 = cachingContainer.getComponent(Cookie::class.java) as Cookie val cookie2 = cachingContainer.getComponent(Cookie::class.java) as Cookie assert(cookie1...

Unable to add Kotlin Android Extensions to my project When i try to add kotlin-android-extensions via: apply plugin: 'realm-android' to my project Android Studio tells me Plugin with 'kotlin-android-extensions not found?? What is going wrong? I am Running Android Studio 3.0 Canary 8

TornadoFX: Label text not updating One of the issues I'm currently experiencing is that I can't seem to change the text of a Label which is implemented in a dynamically loaded AnchorPane. I assume this might be related to the controller and how JavaFX/TornadoFX works, but I can't seem to find what I'm doing wrong. The issue itself occurs in <a...

Android Dagger 2.11 with Kotlin, ContributesAndroidInjector Annotation issue I'm using Dagger 2.11 with Kotlin. Everything is fine with Dagger but when i add ContributesAndroidInjector annotation to project i get this error: e: ...build/tmp/kapt3/stubs/devDebug/com/raqun/android/di/AppComponent.java6 error: dagger.internal.codegen.ComponentProcessor was unable to process this interface because not all of its dependencies could be resolved. Check for compilation errors or a circular dependency with generated code. e: e: public abstract interface AppComponent...