I hope to override onCurrentListChanged of ListAdapter, but Code A doesn't work, how can I fix it?
Code A
myAdapter.onCurrentListChanged(){previousList, currentList ->
}
Added Content
To Alexey Romanov: Thanks!
Code C can work well, but Code D by your answer can not work, what error is there?
Code C
private val myAdapter by lazy{
VoiceAdapters(mHomeViewModel,mPlay)
}
Code D
private val myAdapter by lazy{
VoiceAdapters(mHomeViewModel,mPlay) {
override fun onCurrentListChanged(previousList: MutableList<MVoice>, currentList: MutableList<MVoice>) {
}
}
Both
class VoiceAdapters (private val aHomeViewModel: HomeViewModel, private val mPlay: PlayInterface):
ListAdapter<MVoice, VoiceAdapters.VoiceViewHolder>(MVoiceDiffCallback()) {
...
}
The code you show looks more like an attempt to call onCurrentListChanged, but
that would be simply myAdapter.onCurrentListChanged(someList1, someList2);
it probably shouldn't be called manually.
To override a method of ListAdapter, you need to do it when defining myAdapter (or whatever class it's an instance of). E.g.
val myAdapter = object : ListAdapter<SomeType> {
override fun onCurrentListChanged(previousList: MutableList<SomeType>, currentList: MutableList<SomeType>) {
...
}
// other overrides
}
See object expressions for the explanation and details of object : ... syntax.
When you already have myAdapter, it's too late, though you could create a new ListAdapter which has its own onCurrentListChanged and delegates to myAdapter for other methods. Kotlin has special support for this pattern for interfaces, but ListAdapter is a class and you'd have to do everything manually:
val myAdapter2 = object : ListAdapter<SomeType> {
override fun onCurrentListChanged(previousList: MutableList<SomeType>, currentList: MutableList<SomeType>) {
...
}
override fun getCurrentList() = myAdapter.getCurrentList()
override fun getItemCount() = myAdapter.getItemCount()
// etc.
}
Code C can work well, but Code D by your answer can not work, what error is there?
It should be
private val myAdapter by lazy {
object : VoiceAdapters(mHomeViewModel,mPlay) {
override fun onCurrentListChanged(previousList: MutableList<MVoice>, currentList: MutableList<MVoice>) {
}
}
}
Related
suppose there are 2 classes:
class MyLiveData:LiveData<Int>()
class MyMutableLiveData:MutableLiveData<Int>()
Casting from MutableLiveData to LiveData is permitted:
val ld1=MutableLiveData<Int>()
val ld2:LiveData<Int> = ld1 //ok
But you can't cast your own implementations this way:
val mutable=MyMutableLiveData()
val immutable:MyLiveData = mutable //type missmatch
I understand that MutableLiveData extends LiveData thats why they are castable.But I can't have MyMutableLiveData extending MyLiveData as it won't be mutable in this case
Are there any workarounds?
UPD:I guess I need to show motivation of extending LiveData.I'm trying to implement MutableLiveDataCollection which notifies not just value changes via setValue/postValue but also value modification like adding new elements.I'm surprised there is no native solution for this.
Anyway to obseve modify events there have to be additional observe method.And this method have to be inside immutable part aka LiveDataCollection because views will call it.Inheritance is natural solution here IMHO.
The key idea sits in the MutableLiveData class.The only thing this class does - is it changes access modifiers on setValue/postValue methods.I can do the same trick.Therefore the final code will be:
open class LiveDataCollection<K,
L:MutableCollection<K>,
M:Collection<K>>: LiveData<L>() {
private var active=false
private var diffObservers = ArrayList<Observer<M>>()
fun observe(owner: LifecycleOwner, valueObserver: Observer<L>, diffObserver: Observer<M>) {
super.observe(owner,valueObserver)
diffObservers.add(diffObserver)
}
protected open fun addItems(toAdd:M) {
value?.addAll(toAdd)
if (active)
for (observer in diffObservers)
observer.onChanged(toAdd)
}
override fun removeObservers(owner: LifecycleOwner) {
super.removeObservers(owner)
diffObservers= ArrayList()
}
override fun onActive() {
super.onActive()
active=true
}
override fun onInactive() {
super.onInactive()
active=false
}
}
class MutableLiveDataCollection<K,L:MutableCollection<K>,
M:Collection<K>>: LiveDataCollection<K,L,M>() {
public override fun addItems(toAdd:M) {
super.addItems(toAdd)
}
public override fun postValue(value: L) {
super.postValue(value)
}
public override fun setValue(value: L) {
super.setValue(value)
}
}
Is there any elegant way to apply polymorphism in this case? The parser provides the following classes at runtime:
class io.swagger.v3.oas.models.media.Schema //is parent of the rest :
class io.swagger.v3.oas.models.media.ComposedSchema
class io.swagger.v3.oas.models.media.ArraySchema
class io.swagger.v3.oas.models.media.StringSchema
class io.swagger.v3.oas.models.media.ObjectSchema
I'd like to have function for each class with the same name and simple, short method which will cast and call necessary function at runtime. Which is actually happening, but I hope there is more brief solution, without necessity of making this kind of duplicates:
fun main() {
val parser = OpenAPIV3Parser()
val asList = listOf(pathYaml3, pathYml2)
val map = asList.map(parser::read)
.flatMap { it.components.schemas.values }
.forEach(::parseRawSchema)
}
fun parseRawSchema(schema: Schema<Any>) {
if (schema is ComposedSchema) {
parseSchema(schema)
}
if (schema is StringSchema) {
parseSchema(schema)
}
...
}
fun parseSchema(schema: ComposedSchema) {
println("Compose-schema")
}
fun parseSchema(schema: StringSchema) {
println("Sting-schema")
}
...
Try use extension.
For example:
fun ComposedSchema.parseSchema() {
println("Compose-schema")
}
fun StringSchema.parseSchema() {
println("Sting-schema")
}
And than:
fun parseRawSchema(schema: Schema<Any>) {
schema.parseSchema()
}
How to use method references to refer to super class methods?
In Java 8 you can do SubClass.super::method.
What would be the syntax in Kotlin?
Looking forward to your response!
Conclusion
Thanks to Bernard Rocha!
The syntax is SubClass::method.
But be careful. In my case the subclass was a generic class. Don't forget to declare it as those:
MySubMap<K, V>::method.
EDIT
It still doesn't work in Kotlin.
Hers's an example in Java 8 of a method reference to a super class method:
public abstract class SuperClass {
void method() {
System.out.println("superclass method()");
}
}
public class SubClass extends SuperClass {
#Override
void method() {
Runnable superMethodL = () -> super.method();
Runnable superMethodMR = SubClass.super::method;
}
}
I'm still not able to do the same in Kotlin...
EDIT
This is an example how I tried to achieve it in Kotlin:
open class Bar {
open fun getString(): String = "Hello"
}
class Foo : Bar() {
fun testFunction(action: () -> String): String = action()
override fun getString(): String {
//this will throw an StackOverflow error, since it will continuously call 'Foo.getString()'
return testFunction(this::getString)
}
}
I want to have something like that:
...
override fun getString(): String {
//this should call 'Bar.getString' only once. No StackOverflow error should happen.
return testFunction(super::getString)
}
...
Conclusion
It's not possible to do so in Kotlin yet.
I submitted a feature report. It can be found here: KT-21103 Method Reference to Super Class Method
As the documentation says you use it like in java:
If we need to use a member of a class, or an extension function, it
needs to be qualified. e.g. String::toCharArray gives us an extension
function for type String: String.() -> CharArray.
EDIT
I think you can achieve what you want doing something like this:
open class SuperClass {
companion object {
fun getMyString(): String {
return "Hello"
}
}
}
class SubClass : SuperClass() {
fun getMyAwesomeString(): String {
val reference = SuperClass.Companion
return testFunction(reference::getMyString)
}
private fun testFunction(s: KFunction0<String>): String {
return s.invoke()
}
}
Don't know if it is possible to get the reference to super class's function, but here is an alternative to what you want to achieve:
override fun getString(): String = testFunction { super.getString() }
According to Bernardo's answer, you might have something like this. It doesn't have remarkable changes.
fun methodInActivity() {
runOnUiThread(this::config)
}
fun config(){
}
What is more, in the incoming 1.2 version you can use just
::config
I have a collection of objects which inherit Component and I want a function which finds an object by its concrete class and return it.
But Kotlin does not like the cast I do, and adding #Suppress("UNCHECKED_CAST") is ugly.
I have the following code:
open class GameObjectImpl : GameObject {
private val attachedComponents = mutableSetOf<Component>()
#Suppress("UNCHECKED_CAST")
override fun <TComponent : Component> getComponent(type: KClass<TComponent>): TComponent? {
return attachedComponents.find { type.isInstance(it) } as? TComponent
}
}
This should work for you:
open class GameObjectImpl : GameObject {
val attachedComponents = mutableSetOf<Component>()
override inline fun <reified TComponent : Component> getComponent(type: KClass<TComponent>): TComponent? {
return attachedComponents.filterIsInstance<TComponent>().firstOrNull()
}
}
I have a framework written in Java that, using reflection, get the fields on an annotation and make some decisions based on them. At some point I am also able to create an ad-hoc instance of the annotation and set the fields myself. This part looks something like this:
public #interface ThirdPartyAnnotation{
String foo();
}
class MyApp{
ThirdPartyAnnotation getInstanceOfAnnotation(final String foo)
{
ThirdPartyAnnotation annotation = new ThirdPartyAnnotation()
{
#Override
public String foo()
{
return foo;
}
};
return annotation;
}
}
Now I am trying to do the exact thing in Kotlin. Bear in mind that the annotation is in a third party jar.
Anyway, here is how I tried it in Kotlin:
class MyApp{
fun getAnnotationInstance(fooString:String):ThirdPartyAnnotation{
return ThirdPartyAnnotation(){
override fun foo=fooString
}
}
But the compiler complains about: Annotation class cannot be instantiated
So the question is: how should I do this in Kotlin?
You can do this with Kotlin reflection:
val annotation = ThirdPartyAnnotation::class.constructors.first().call("fooValue")
In the case of annotation having no-arg constructor (e.g. each annotation field has a default value), you can use following approach:
annotation class SomeAnnotation(
val someField: Boolean = false,
)
val annotation = SomeAnnotation::class.createInstance()
This is the solution I might have found but feels like a hack to me and I would prefer to be able to solve it within the language.
Anyway, for what is worth,it goes like this:
class MyApp {
fun getInstanceOfAnnotation(foo: String): ThirdPartyAnnotation {
val annotationListener = object : InvocationHandler {
override fun invoke(proxy: Any?, method: Method?, args: Array<out Any>?): Any? {
return when (method?.name) {
"foo" -> foo
else -> FindBy::class.java
}
}
}
return Proxy.newProxyInstance(ThirdPartyAnnotation::class.java.classLoader, arrayOf(ThirdPartyAnnotation::class.java), annotationListener) as ThirdPartyAnnotation
}
}