Kotlin provides the ability to extend a class with new functionality without having to inherit from the class or use any type of design pattern such as Decorator. This is done via special declarations called extensions.
Questions tagged [kotlin-extension]
333 questions
24
votes
3 answers
Android Java Project Converts to Kotlin in Android Studio
I want to convert my java project to Kotlin, there are more than 500 java files. How can I convert it into Kotlin easily?
I know that we can convert one by one java file to Kotlin, But there are many files.
Can I convert it at once?
Samir Mangroliya
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23
votes
3 answers
Extension functions for generic classes in Kotlin
What's wrong with my extension function below
class Foo {
fun Foo.plus(that: Foo): Foo = throw Exception()
init {
Foo() + Foo() // A receiver of type Foo is required
}
}
Update
I wonder why it's…
Yaroslav
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21
votes
5 answers
Cannot resolve symbol repeatOnLifecycle in Android
I'm following this article to collect flows in UI. But I couldn't resolve repeatOnLifeCycle API in my code. I have added the below dependency, though.
lifecycle:lifecycle-runtime-ktx:2.4.0-alpha03
Please help
Rakesh
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21
votes
4 answers
Kotlin: How to extend the enum class with an extension function
I'm trying to extend enum classes of type String with the following function but am unable to use it at the call site like so:
fun > Class.join(skipFirst: Int = 0, skipLast: Int = 0): String {
return this.enumConstants
…
geg
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19
votes
1 answer
Kotlin synthetic extension for view
I have a layout with some views, one of them has the id title_whalemare
import kotlinx.android.synthetic.main.controller_settings.*
import kotlinx.android.synthetic.main.view_double_text.*
class MainSettingsController : BaseMvpController
whalemare
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18
votes
1 answer
Kotlin Android: Property delegate must have a 'getValue(DashViewModel, KProperty*>)' method
I am trying to follow the official Android guide for ViewModels in Kotlin.
I literally copy pasted the easiest official example but the syntax seems to be illegal.
This section causes the problem:
private val users: MutableLiveData> by…
user123456789
- 301
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18
votes
4 answers
how to instantiate an object from a class in kotlin
I am learning Kotlin, and I googled how to create a class in kotlin. So, I created the below class as a test.
In the main activity, I am trying to instantiate an object from the class Board, but i get the following error:
classifier Board does not…
Amrmsmb
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18
votes
3 answers
Modify "this" in extension function
I want to write extension function that modifies "this", for example:
var a = false
a.toggle() // now a contains false
or
var a = 1
a.increment() // now a contains 2
Is it possible in Kotlin?
I can create extension function that returns modified…
Dmitry Ryadnenko
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17
votes
1 answer
how to use the new extension functions in okhttp 4
Hi got this compile error when upgrading from okHttp version 3 to version 4:
val JSON = MediaType.parse("application/json; charset=utf-8")
//Compile Error: Kotlin: Using 'parse(String): MediaType?' is an error. moved to extension function
I changed…
MiguelSlv
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17
votes
2 answers
Kotlin Extension Functions - Override existing method
is it possible to do something like:
/**
* Converts all of the characters in the string to upper case.
*
* @param str the string to be converted to uppercase
* @return the string converted to uppercase or empty string if the input was null
…
Psest328
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16
votes
2 answers
kotlin extension method access in another kt
I'm thinking about adding a global extension method to String in just one file,and wherever i use a String i can always use this extension.
But i failed to find a way to do so...i just paste the extension everywhere now.
extension here in…
Draculea
- 303
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- 7
16
votes
1 answer
Unit test on Kotlin Extension Function on Android SDK Classes
Kotlin extension function is great. But how could I perform unit test on them? Especially those that is of Android SDK provided class (e.g. Context, Dialog).
I provide two examples below, and if anyone could share how I could unit test them, or if I…
Elye
- 53,639
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16
votes
2 answers
Use Kotlin extension in android java class
Is it possible to use a kotlin extension in a android java class?
Example:
fun String.getSomething(): String {
return "something"
}
then in Java use it like:
String someString = "blabla";
someString.getSomething();
is this possible?
Informatic0re
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15
votes
4 answers
Kotlin extension functions vs member functions?
I am aware that extension functions are used in Kotlin to extend the functionality of a class (for example, one from a library or API).
However, is there any advantage, in terms of code readability/structure, by using extension functions:
class Foo…
Farbod Salamat-Zadeh
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15
votes
4 answers
this reference in a lazy initializer of kotlin extension property
I'm trying Kotlin and want to implement a lazy extension property for Activity:
/**
* Activity module
*/
val Activity.activityModule: ActivityModule by lazy {
ActivityModule(this)
}
The compiler errors with:
'this' is not defined in this…
Motorro
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