I run Code A, and get the error Result A. It seems that isRecordingState has't been initialized.
So I modify Code A as Code B, and Code B can run correctly.
In my mind, I can place different functions in any order in a class of Kotlin.
I think init{ } of a Class will be launched after the object has been initialized, so I think I can place init{ } in any place of a class.
What's wrong with my ideas?
Code A
#HiltViewModel
class SoundViewModel #Inject constructor(
#ApplicationContext private val appContext: Context,
...
): ViewModel() {
init { beginSoundDensity() }
private val _timeXState = MutableStateFlow(0)
var isRecordingState by mutableStateOf(false)
private set
private var myJob: Job?=null
fun beginSoundDensity() {
if (isRecordingState == false) {
isRecordingState = true
myJob?.cancel()
...
}
}
}
Result A
java.lang.NullPointerException: Attempt to invoke interface method 'java.lang.Object androidx.compose.runtime.State.getValue()' on a null object reference
at info.dodata.soundmeter.presentation.viewmodel.SoundViewModel.isRecordingState(SoundViewModel.kt:245)
at info.dodata.soundmeter.presentation.viewmodel.SoundViewModel.beginSoundDensity(SoundViewModel.kt:81)
at info.dodata.soundmeter.presentation.viewmodel.SoundViewModel.<init>(SoundViewModel.kt:39)
Code B
#HiltViewModel
class SoundViewModel #Inject constructor(
#ApplicationContext private val appContext: Context,
...
): ViewModel() {
private val _timeXState = MutableStateFlow(0)
var isRecordingState by mutableStateOf(false)
private set
private var myJob: Job?=null
init { beginSoundDensity() }
fun beginSoundDensity() {
if (isRecordingState == false) {
isRecordingState = true
myJob?.cancel()
...
}
}
}
The code just runs from top to bottom, so this code for example prints "12345"
fun main() {
A()
}
class A {
init {
print("1")
}
val s2 = printAndReturn("2")
init {
print("3")
}
val s4 = printAndReturn("4")
init {
print("5")
}
private fun printAndReturn(s: String): String {
print(s)
return s
}
}
I've been trying to test my view model for several days without success.
This is my view model :
class AdvertViewModel : ViewModel() {
private val parentJob = Job()
private val coroutineContext: CoroutineContext
get() = parentJob + Dispatchers.Default
private val scope = CoroutineScope(coroutineContext)
private val repository : AdvertRepository = AdvertRepository(ApiFactory.Apifactory.advertService)
val advertContactLiveData = MutableLiveData<String>()
fun fetchRequestContact(requestContact: RequestContact) {
scope.launch {
val advertContact = repository.requestContact(requestContact)
advertContactLiveData.postValue(advertContact)
}
}
}
This is my repository :
class AdvertRepository (private val api : AdvertService) : BaseRepository() {
suspend fun requestContact(requestContact: RequestContact) : String? {
val advertResponse = safeApiCall(
call = {api.requestContact(requestContact).await()},
errorMessage = "Error Request Contact"
)
return advertResponse
}
}
This is my view model test :
#RunWith(JUnit4::class)
class AdvertViewModelTest {
private val goodContact = RequestContact(...)
private lateinit var advertViewModel: AdvertViewModel
private var observer: Observer<String> = mock()
#get:Rule
var instantTaskExecutorRule = InstantTaskExecutorRule()
#Before
fun setUp() {
advertViewModel = AdvertViewModel()
advertViewModel.advertContactLiveData.observeForever(observer)
}
#Test
fun fetchRequestContact_goodResponse() {
advertViewModel.fetchRequestContact(goodContact)
val captor = ArgumentCaptor.forClass(String::class.java)
captor.run {
verify(observer, times(1)).onChanged(capture())
assertEquals("someValue", value)
}
}
}
The method mock() :
inline fun <reified T> mock(): T = Mockito.mock(T::class.java)
I got this error :
Wanted but not invoked: observer.onChanged();
-> at com.vizzit.AdvertViewModelTest.fetchRequestContact_goodResponse(AdvertViewModelTest.kt:52)
Actually, there were zero interactions with this mock.
I don't understand how to retrieve the result of my query.
You would need to write a OneTimeObserver to observe livedata from the ViewModel
class OneTimeObserver<T>(private val handler: (T) -> Unit) : Observer<T>, LifecycleOwner {
private val lifecycle = LifecycleRegistry(this)
init {
lifecycle.handleLifecycleEvent(Lifecycle.Event.ON_RESUME)
}
override fun getLifecycle(): Lifecycle = lifecycle
override fun onChanged(t: T) {
handler(t)
lifecycle.handleLifecycleEvent(Lifecycle.Event.ON_DESTROY)
}
}
After that you can write an extension function:
fun <T> LiveData<T>.observeOnce(onChangeHandler: (T) -> Unit) {
val observer = OneTimeObserver(handler = onChangeHandler)
observe(observer, observer)
}
Than you can check this ViewModel class class that I have from a project to check what's going on with your LiveData after you act (when) with invoking a method.
As for your error, it just says that the onChanged() method is not being called ever.
I request data from server by bunches and store it in the array.To track fetching of the next bunch of the data I have this class.In the addItems method I notify diffObservers and pass list of new items:
class PackItems:MutableLiveData<ArrayList<GetPacksResponse.PackData>>() {
private var diffObservers=ArrayList<Observer<List<GetPacksResponse.PackData>>>()
private var active=false
fun observeItems(owner: LifecycleOwner, valueObserver:Observer<List<GetPacksResponse.PackData>>,diffObserver:Observer<List<GetPacksResponse.PackData>>) {
super.observe(owner,valueObserver)
diffObservers.add(diffObserver)
}
override fun removeObservers(owner: LifecycleOwner) {
super.removeObservers(owner)
diffObservers= ArrayList()
}
fun addItems(toAdd:List<GetPacksResponse.PackData>) {
value?.addAll(toAdd)
if (active)
for (observer in diffObservers)
observer.onChanged(toAdd)
}
override fun onActive() {
super.onActive()
active=true
}
override fun onInactive() {
super.onInactive()
active=false
}
}
The problem is PackItems is MutableLiveData and it's not good practice to expose it.Is there way to cast it to LiveData?Like usually we do:
private val _items = MutableLiveData<List<Int>>()
val items: LiveData<List<Int>> = _items
UPD:Ideally would be if I could expose completely immutable LiveData.But I can't just write
private val _packs:PackItems=PackItems()
val packs:LiveData<ArrayList<GetPacksResponse.PackData>>
get()=_packs
Because in this case packs won't contain observeItems method.Therefore there must be custom class derived from LiveData like:
open class PackItems: LiveData<ArrayList<GetPacksResponse.PackData>>() {
protected var active=false
protected var diffObservers = ArrayList<Observer<List<GetPacksResponse.PackData>>>()
fun observeItems(owner: LifecycleOwner, valueObserver: Observer<List<GetPacksResponse.PackData>>, diffObserver: Observer<List<GetPacksResponse.PackData>>) {
super.observe(owner,valueObserver)
diffObservers.add(diffObserver)
}
//...
}
class MutablePackItems: PackItems() {
fun addItems(toAdd:List<GetPacksResponse.PackData>) {
value?.addAll(toAdd)
if (active)
for (observer in diffObservers)
observer.onChanged(toAdd)
}
}
But in this case I won't be able to set data because now MutablePackItems is LiveData(immutable) :)
I'd consider using composition instead of inheritance:
class PackItems() {
private val mutableData = MutableLiveData<ArrayList<GetPacksResponse.PackData>>()
val asLiveData: LiveData<ArrayList<GetPacksResponse.PackData>> get() = mutableData
...
fun observeItems(owner: LifecycleOwner, valueObserver:Observer<List<GetPacksResponse.PackData>>,diffObserver:Observer<List<GetPacksResponse.PackData>>) {
mutableData.observe(owner,valueObserver)
diffObservers.add(diffObserver)
}
fun removeObservers(owner: LifecycleOwner) {
mutableData.removeObservers(owner)
diffObservers = ArrayList()
}
// etc
}
EDIT: to set active as in your original code, may be a bit nastier:
private val mutableData = object : MutableLiveData<ArrayList<GetPacksResponse.PackData>>() {
override fun onActive() {
super.onActive()
active = true
}
override fun onInactive() {
super.onInactive()
active = false
}
}
EDIT 2:
but the main problem is I need to return custom LiveData class with custom observeItems method
The point is that you don't necessarily. Whenever you'd call LiveData's method (e.g. observe), just call items.asLiveData.observe(...) instead. If you want to pass it to another method foo accepting LiveData, call foo(items.asLiveData).
In principle, you could modify this approach by extending LiveData and delegating all calls to mutableData:
class PackItems(): LiveData<ArrayList<GetPacksResponse.PackData>>() {
private val mutableData = MutableLiveData<ArrayList<GetPacksResponse.PackData>>()
...
fun observeItems(owner: LifecycleOwner, valueObserver:Observer<List<GetPacksResponse.PackData>>,diffObserver:Observer<List<GetPacksResponse.PackData>>) {
mutableData.observe(owner,valueObserver)
diffObservers.add(diffObserver)
}
override fun observe(owner: LifecycleOwner, observer: ArrayList<GetPacksResponse.PackData>) {
mutableData.observe(owner, observer)
}
override fun removeObservers(owner: LifecycleOwner) {
mutableData.removeObservers(owner) // not super!
diffObservers = ArrayList()
}
// etc
}
but I don't think it's a good idea.
I want to create an easier way to handle SharedPreferences.
The way I want to call it is like this
get preference:
val email = SharedPrefs.userdata.email
val wifiOnly = SharedPrefs.connections.wifiOnly
set preference:
SharedPrefs.userdata.email = "someone#example.com"
SharedPrefs.connections.wifiOnly = true
I'm able to do so like this:
App.instance returns a Context object in the following snippet
object SharedPrefs {
val userdata by lazy { UserPreferences() }
val connections by lazy { ConnectionPreferences() }
class UserPreferences {
private val prefs: SharedPreferences = App.instance.getSharedPreferences("userdata", Context.MODE_PRIVATE)
var email: String
get() = prefs.getString("email", null)
set(value) = prefs.edit().putString("email", value).apply()
}
class ConnectionPreferences {
private val prefs: SharedPreferences = App.instance.getSharedPreferences("connections", Context.MODE_PRIVATE)
var wifyOnly: Boolean
get() = prefs.getBoolean("wifiOnly", false)
set(value) = prefs.edit().putBoolean("wifyOnly", value).apply()
}
}
The problem is that this can still be called: SharedPrefs.UserPreferences()
Can I make this constructor private to this file or object only?
You can separate the interface and the implementation class, and make the latter private to the object:
object SharedPrefs {
val userdata: UserPreferences by lazy { UserPreferencesImpl() }
interface UserPreferences {
var email: String
}
private class UserPreferencesImpl : UserPreferences {
private val prefs: SharedPreferences =
App.instance.getSharedPreferences("userdata", Context.MODE_PRIVATE)
override var email: String
get() = prefs.getString("email", null)
set(value) = prefs.edit().putString("email", value).apply()
}
// ...
}
Alternatively, if you are developing a library or you have a modular architecture, you can make use of the internal visibility modifier to restrict the visibility to the module:
class UserPreferences internal constructor() { /* ... */ }
You can try something like this
class UserPreferences private constructor()
{
// your impl
}
This is the reference
Suppose I only want one or two fields to be included in the generated equals and hashCode implementations (or perhaps exclude one or more fields). For a simple class, e.g.:
data class Person(val id: String, val name: String)
Groovy has this:
#EqualsAndHashCode(includes = 'id')
Lombok has this:
#EqualsAndHashCode(of = "id")
What is the idiomatic way of doing this in Kotlin?
My approach so far
data class Person(val id: String) {
// at least we can guarantee it is present at access time
var name: String by Delegates.notNull()
constructor(id: String, name: String): this(id) {
this.name = name
}
}
Just feels wrong though... I don't really want name to be mutable, and the extra constructor definition is ugly.
I've used this approach.
data class Person(val id: String, val name: String) {
override fun equals(other: Person) = EssentialData(this) == EssentialData(other)
override fun hashCode() = EssentialData(this).hashCode()
override fun toString() = EssentialData(this).toString().replaceFirst("EssentialData", "Person")
}
private data class EssentialData(val id: String) {
constructor(person: Person) : this(id = person.id)
}
This approach may be suitable for property exclusion:
class SkipProperty<T>(val property: T) {
override fun equals(other: Any?) = true
override fun hashCode() = 0
}
SkipProperty.equals simply returns true, which causes the embeded property to be skipped in equals of parent object.
data class Person(
val id: String,
val name: SkipProperty<String>
)
I also don't know "the idomatic way" in Kotlin (1.1) to do this...
I ended up overriding equals and hashCode:
data class Person(val id: String,
val name: String) {
override fun equals(other: Any?): Boolean {
if (this === other) return true
if (other?.javaClass != javaClass) return false
other as Person
if (id != other.id) return false
return true
}
override fun hashCode(): Int {
return id.hashCode()
}
}
Isn't there a "better" way?
This builds on #bashor's approach and uses a private primary and a public secondary constructor. Sadly the property to be ignored for equals cannot be a val, but one can hide the setter, so the result is equivalent from an external perspective.
data class ExampleDataClass private constructor(val important: String) {
var notSoImportant: String = ""
private set
constructor(important: String, notSoImportant: String) : this(important) {
this.notSoImportant = notSoImportant
}
}
Here's a somewhat creative approach:
data class IncludedArgs(val args: Array<out Any>)
fun includedArgs(vararg args: Any) = IncludedArgs(args)
abstract class Base {
abstract val included : IncludedArgs
override fun equals(other: Any?) = when {
this identityEquals other -> true
other is Base -> included == other.included
else -> false
}
override fun hashCode() = included.hashCode()
override fun toString() = included.toString()
}
class Foo(val a: String, val b : String) : Base() {
override val included = includedArgs(a)
}
fun main(args : Array<String>) {
val foo1 = Foo("a", "b")
val foo2 = Foo("a", "B")
println(foo1 == foo2) //prints "true"
println(foo1) //prints "IncludedArgs(args=[a])"
}
Reusable solution: to have an easy way to select which fields to include in equals() and hashCode(), I wrote a little helper called "stem" (essential core data, relevant for equality).
Usage is straightforward, and the resulting code very small:
class Person(val id: String, val name: String) {
private val stem = Stem(this, { id })
override fun equals(other: Any?) = stem.eq(other)
override fun hashCode() = stem.hc()
}
It's possible to trade off the backing field stored in the class with extra computation on-the-fly:
private val stem get() = Stem(this, { id })
Since Stem takes any function, you are free to specify how the equality is computed. For more than one field to consider, just add one lambda expression per field (varargs):
private val stem = Stem(this, { id }, { name })
Implementation:
class Stem<T : Any>(
private val thisObj: T,
private vararg val properties: T.() -> Any?
) {
fun eq(other: Any?): Boolean {
if (thisObj === other)
return true
if (thisObj.javaClass != other?.javaClass)
return false
// cast is safe, because this is T and other's class was checked for equality with T
#Suppress("UNCHECKED_CAST")
other as T
return properties.all { thisObj.it() == other.it() }
}
fun hc(): Int {
// Fast implementation without collection copies, based on java.util.Arrays.hashCode()
var result = 1
for (element in properties) {
val value = thisObj.element()
result = 31 * result + (value?.hashCode() ?: 0)
}
return result
}
#Deprecated("Not accessible; use eq()", ReplaceWith("this.eq(other)"), DeprecationLevel.ERROR)
override fun equals(other: Any?): Boolean =
throw UnsupportedOperationException("Stem.equals() not supported; call eq() instead")
#Deprecated("Not accessible; use hc()", ReplaceWith("this.hc(other)"), DeprecationLevel.ERROR)
override fun hashCode(): Int =
throw UnsupportedOperationException("Stem.hashCode() not supported; call hc() instead")
}
In case you're wondering about the last two methods, their presence makes the following erroneous code fail at compile time:
override fun equals(other: Any?) = stem.equals(other)
override fun hashCode() = stem.hashCode()
The exception is merely a fallback if those methods are invoked implicitly or through reflection; can be argued if it's necessary.
Of course, the Stem class could be further extended to include automatic generation of toString() etc.
Simpler, faster, look at there, or into the Kotlin documentation.
https://discuss.kotlinlang.org/t/ignoring-certain-properties-when-generating-equals-hashcode-etc/2715/2
Only fields inside the primary constructor are taken into account to build automatic access methods like equals and so on. Do keep the meaningless ones outside.
Here is another hacky approach if you don't want to touch the data class.
You can reuse the entire equals() from data classes while excluding some fields.
Just copy() the classes with fixed values for excluded fields:
data class Person(val id: String,
val name: String)
fun main() {
val person1 = Person("1", "John")
val person2 = Person("2", "John")
println("Full equals: ${person1 == person2}")
println("equals without id: ${person1.copy(id = "") == person2.copy(id = "")}")
}
Output:
Full equals: false
equals without id: true
Consider the following generic approach for the implementation of equals/hashcode. The code below should have no performance impact because of the use of inlining and kotlin value classes:
#file:Suppress("EXPERIMENTAL_FEATURE_WARNING")
package org.beatkit.common
import kotlin.jvm.JvmInline
#Suppress("NOTHING_TO_INLINE")
#JvmInline
value class HashCode(val value: Int = 0) {
inline fun combineHash(hash: Int): HashCode = HashCode(31 * value + hash)
inline fun combine(obj: Any?): HashCode = combineHash(obj.hashCode())
}
#Suppress("NOTHING_TO_INLINE")
#JvmInline
value class Equals(val value: Boolean = true) {
inline fun combineEquals(equalsImpl: () -> Boolean): Equals = if (!value) this else Equals(equalsImpl())
inline fun <A : Any> combine(lhs: A?, rhs: A?): Equals = combineEquals { lhs == rhs }
}
#Suppress("NOTHING_TO_INLINE")
object Objects {
inline fun hashCode(builder: HashCode.() -> HashCode): Int = builder(HashCode()).value
inline fun hashCode(vararg objects: Any?): Int = hashCode {
var hash = this
objects.forEach {
hash = hash.combine(it)
}
hash
}
inline fun hashCode(vararg hashes: Int): Int = hashCode {
var hash = this
hashes.forEach {
hash = hash.combineHash(it)
}
hash
}
inline fun <T : Any> equals(
lhs: T,
rhs: Any?,
allowSubclasses: Boolean = false,
builder: Equals.(T, T) -> Equals
): Boolean {
if (rhs == null) return false
if (lhs === rhs) return true
if (allowSubclasses) {
if (!lhs::class.isInstance(rhs)) return false
} else {
if (lhs::class != rhs::class) return false
}
#Suppress("unchecked_cast")
return builder(Equals(), lhs, rhs as T).value
}
}
With this in place, you can easily implement/override any equals/hashcode implementation in a uniform way:
data class Foo(val title: String, val bytes: ByteArray, val ignore: Long) {
override fun equals(other: Any?): Boolean {
return Objects.equals(this, other) { lhs, rhs ->
this.combine(lhs.title, rhs.title)
.combineEquals { lhs.bytes contentEquals rhs.bytes }
// ignore the third field for equals
}
}
override fun hashCode(): Int {
return Objects.hashCode(title, bytes) // ignore the third field for hashcode
}
}
You can create an annotation that represents the exclusion of the property as #ExcludeToString or with #ToString(Type.EXCLUDE) parameters by defining enum.
And then using reflection format the value of the getToString().
#Target(AnnotationTarget.FIELD)
#Retention(AnnotationRetention.RUNTIME)
annotation class ExcludeToString
data class Test(
var a: String = "Test A",
#ExcludeToString var b: String = "Test B"
) {
override fun toString(): String {
return ExcludeToStringUtils.getToString(this)
}
}
object ExcludeToStringUtils {
fun getToString(obj: Any): String {
val toString = LinkedList<String>()
getFieldsNotExludeToString(obj).forEach { prop ->
prop.isAccessible = true
toString += "${prop.name}=" + prop.get(obj)?.toString()?.trim()
}
return "${obj.javaClass.simpleName}=[${toString.joinToString(", ")}]"
}
private fun getFieldsNotExludeToString(obj: Any): List<Field> {
val declaredFields = obj::class.java.declaredFields
return declaredFields.filterNot { field ->
isFieldWithExludeToString(field)
}
}
private fun isFieldWithExludeToString(field: Field): Boolean {
field.annotations.forEach {
if (it.annotationClass == ExcludeToString::class) {
return true
}
}
return false
}
}
GL
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