kotlinlang #getting-started

that version 1.3.72 seems to support Java13, but when I try it out I get the error “Unsupported class file major version 57”, which made me wonder if it was supported after all? 🤔

Tom Carton

04/29/2020, 9:44 AM

Hey! I'm quite stuck on a custom project I'm working on and I'm pretty sure I could greatly learn and improve it with your insights! I'm trying to develop a custom

Chat Mobile Application

as such: - a server in

Kotlin

- clients using

KotlinMultiplatform/Kotlin-native

I want to use sockets to exchange encrypted messages (using a simple xor for instance) in the common/shared part using Posix. Each client displays all the messages and can send new message to the server. The server serves all the clients with any message it received. Nothing fancy on that side... And the main thing I am trying to demonstrate with all this, is how I could share the maximum of code between platforms using

Kotlin-native

and have clients code only responsible for the UI. Period. So I tried to use

Coroutines

to have a background thread listening to incoming messages. These messages could come from socket (in order to be dispatched to the UI) or from UI (in order to be dispatched to socket). But sounds like it doesn't work like this as my application often get stuck or the coroutines stop running. I tried to use a heartbeat to wakeup the coroutines or some time-out to prevent getting stuck but this is clearly black magic and doesn't succeed anyway. Do you have any idea or insight to point out on what I should rather do? or on what I am doing wrong? Thank you!

Chilli

04/29/2020, 9:29 PM

For some reason my code stops between those 2 printlns. It prints

init start

and after a few seconds, displays

Test running process exited unexpectedly.

Any idea what might it be? str is String used is MutableSet<String>

poohbar

04/30/2020, 1:41 PM

How do I do this if entity is nullable?

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entity::class

Yevhenii Nadtochii

04/30/2020, 2:04 PM

Hello! Does anybody know how can I use inner classes to delegate interface implementation ?

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interface Action
class Outer(doer: Doer = this.Doer()) : Action by doer { //'this' is not defined in this context
    inner class Doer : Action
}

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interface Action
class Outer : Action by Doer() { //Constructor of inner class Doer can be called only with receiver of containing class
    inner class Doer : Action
}

Nicolò

04/30/2020, 9:36 PM

Hello, I’m having an hard time having a spring boot kotlin app to hotreload/hot swap with intellij. Is there anything i’m missing? I tried to set the auto build setting and the registry to alllow when doing it when the app is running but still not luck!

Alex Kuznetsov

05/01/2020, 8:01 PM

Hi there, Is there a way to have a multi-line statement, a way to tell Kotlin that the statement continues on next line: I'd like to spread a long statement like the following over several lines:

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every { <http://myThing.do|myThing.do>() } returns 1 andThenThrows Exception("No way!") andThen 3 andThen 4

the line gets too wide, is there a way to continue it:

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every { <http://myThing.do|myThing.do>() } returns 1 
  andThenThrows Exception("No way!") 
  andThen 3 
  andThen 4

TIA!

Sudhir Singh Khanger

05/04/2020, 12:47 PM

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private fun twoSome(nums: IntArray, target: Int): IntArray {
    val returnArray: IntArray = intArrayOf()
    var initialVal = nums[0]
    for (num in nums) {
        if (initialVal + num == target) {
            returnArray[0] = initialVal
            returnArray[1] = num
            break
        }
        initialVal = num
    }
    return returnArray
}

Why am I getting

ArrayIndexOutOfBoundsException

when assigning a value to the

returnArray

voben

05/06/2020, 2:25 PM

Is it possible to make a sealed class parcelable? I’ve annotated the child classes with `@Parcelize`but when I add the annotation to the parent, I get an error saying “Parcelable should not be a ‘sealed’ or ‘abstract’ class”

Łukasz Patro

05/11/2020, 9:59 AM

Hi, I could not build Kotlin project using Maven and JDK 6:

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[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 1.635s
[INFO] Finished at: Mon May 11 11:52:50 CEST 2020
[INFO] Final Memory: 7M/231M
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.jetbrains.kotlin:kotlin-maven-plugin:1.3.72:compile (compile) on project untitled: Execution compile of goal org.jetbrains.kotlin:kotlin-maven-plugin:1.3.72:compile failed: Unable to load the mojo 'compile' in the plugin 'org.jetbrains.kotlin:kotlin-maven-plugin:1.3.72' due to an API incompatibility: org.codehaus.plexus.component.repository.exception.ComponentLookupException: org/jetbrains/kotlin/maven/K2JVMCompileMojo : Unsupported major.minor version 52.0

It builds fine with JDK 8.

pom.xml

is very simple:

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<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="<http://maven.apache.org/POM/4.0.0>" xmlns:xsi="<http://www.w3.org/2001/XMLSchema-instance>" xsi:schemaLocation="<http://maven.apache.org/POM/4.0.0> <http://maven.apache.org/maven-v4_0_0.xsd>">

    <modelVersion>4.0.0</modelVersion>

    <groupId>org.example</groupId>
    <artifactId>untitled</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>jar</packaging>

    <name>org.example untitled</name>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <kotlin.version>1.3.72</kotlin.version>
        <kotlin.code.style>official</kotlin.code.style>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.jetbrains.kotlin</groupId>
            <artifactId>kotlin-stdlib</artifactId>
            <version>${kotlin.version}</version>
        </dependency>
    </dependencies>

    <build>
        <sourceDirectory>src/main/kotlin</sourceDirectory>
        <testSourceDirectory>src/test/kotlin</testSourceDirectory>

        <plugins>
            <plugin>
                <groupId>org.jetbrains.kotlin</groupId>
                <artifactId>kotlin-maven-plugin</artifactId>
                <version>${kotlin.version}</version>
                <executions>
                    <execution>
                        <id>compile</id>
                        <phase>compile</phase>
                        <goals>
                            <goal>compile</goal>
                        </goals>
                    </execution>
                    <execution>
                        <id>test-compile</id>
                        <phase>test-compile</phase>
                        <goals>
                            <goal>test-compile</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>
</project>

It seems that

kotlin-maven-plugin

do not support Java before version 8...

Cupi Vo

05/12/2020, 12:40 AM

Hello, Abstract Class vs. Interface: Except that it can only inherit 1 class, is there anything else in the interface that abstract classes cannot? Thanks.

Anton

05/12/2020, 2:31 PM

Hi there. Is it possible to write a function, that accepts a function with any number of arguments, of any kind, and execute it? The following works, but only for lambda functions

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fun <R>myFunc(block: () -> R): R
{
    println("starting)
    try
    {
        return block()
    }
    finally
    {
        println("end")
    }
}

As in the example above, I would like to do some things before the functions run, and some things after. An example would be to measure the execution time. Appreciate any help!

Kevin

05/13/2020, 6:14 PM

Hi all, i would like to know if it is possible to show/hide UI element over a two separated activity? in example, i had to 2 activities, first is the main activity(home) and second is the support activity(something like information or pop up). from this examples i want to somehow show the support activity overlaying the main activity, so far i able to do this by doing

include

of the support activity layout on the main activity file. the next thing i want to do, is that i want to be able to interact with the support activity, which is the basic interaction was only a show/hide elements. i was thinking that i should be able to do this by using

visibility = View.GONE

visibility = View.VISIBLE

on the textview element, but no matter what i do, everytime i click on the textview, it results in the app crashing. i'm quite stuck on this part, do anyone have any idea or insight on where do i wrong? or what should i do? thank you!

still-dreaming-1

05/13/2020, 8:10 PM

What does it mean to have a property that is a val (not var) with a get() function attached, and no set() function. It kind of seems like a contraction of terms to have a "val" that changes every time you "get" it. Will the get be called each time or is it gotten once and then reused?

Mauricio Barbosa

05/13/2020, 8:36 PM

Hi guys, I'm trying to convert an rxjava api based into a suspend function. Can I do something like this?

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class UserApiClient(private val rxJavaBasedApi) {
    suspend fun getUser(): User = withContext(<http://Dispatchers.IO|Dispatchers.IO>) {
        rxJavaBasedApi.getUser().blockingGet()
    }
}

Or there's a better approach?

Kevin

05/14/2020, 3:48 PM

Hi All, I'm trying to change the background of 2 layouts by using onClick. let's say there is Layout A and Layout B, the default form is that Layout A is active and Layout B is inactive, when the user click the button, Layout A become inactive and Layout B become active. active layout will use vector assets as background, while inactive layout will use simple color code(hexcode). to do that i was thinking this can be done by a simple ifelse function, did i do it right with this? or there is a better way to do this?

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var isColorChanged: Boolean? = true;

fun changeScreenClick(view: View) {
        if(isColorChanged==true){
            view_menu_1.resources.getColor(R.color.Yellow)
        }
        else{
            view_menu_2.resources.getDrawable(R.drawable.background_box)
        }
    }

Thank you!

Karlo Lozovina

05/16/2020, 10:31 PM

Total Kotlin/Java/JVM beginner here: managed to deserialize some complex JSON with

kotlinx.serialization

, just can't figure out how to deserialize to

LocalDateTime

Ananiya

05/17/2020, 7:51 AM

if I parse json list file from api server and change it to dataclass if it is

val l = listOf(d1, d2, d3 ,d4 ,d7)

. how do i select the last element in the list but i cannot use

l[5]

l.get(5)

because they may change the list length in any time ?

Mark

05/17/2020, 12:19 PM

Is there anything in the standard library for building an iterator from a list of iterables?

supra

05/18/2020, 5:49 AM

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when (func()) {
    in S -> println("$it in S")
    null -> println("null")
    else -> println("$it not in S")
}

Mark

05/18/2020, 6:55 AM

Is there a simpler version of zip, that doesn’t build a sequence? Rather, we just do the work in the transform block?

bodiam

05/18/2020, 10:52 AM

I'm having a few instances of this in my code:

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return doubleArrayOf(base, tokenSort, tokenSet).max()!!.toInt()

And I'd like to get rid of the

!!

here, especially since I know this call will never return null. Any suggestions on how to do this?

Hixie

05/19/2020, 3:32 AM

is there a kotlin native websocket client library or should we just proxy that to platform-specific code?

frogger

05/19/2020, 10:55 AM

overriding this java method, how can I add a new item to the map?

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override fun extractAuthentication(map: MutableMap<String, *>)

e.g. when I want to add a list the compiler says: “Required Any? found List<String>”

Joshua Akinsola

05/20/2020, 10:49 AM

Hey, I am getting started on android studio and I ran into "no target device found" when trying to run code, any tips on solving this?

google 2

Raj Trivedi

05/20/2020, 11:15 AM

please firrst create device from "AVD Manager"

👍 1

05/20/2020, 2:42 PM

Is there a way to abort early (break) while using

fold

? Or is a normal

for

loop the only option?

Joshua Akinsola

05/20/2020, 3:36 PM

Does anyone know of any courses that show how to build an app on top of Google cloud's infra?