I have a dynamic Json and I am trying to parse it like this
obs.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
.unsubscribeOn(Schedulers.io())
.subscribe(object: Observer <Response<Any>> {
override fun onComplete() {}
override fun onSubscribe(d: Disposable) {}
override fun onNext(t: Response<Any>) {
if (t.code() != 400) {
val registerResponse = t.body() as RegisterResponse?
//this is null
println("value of register resp " + registerResponse?.status)
liveData.value = t.body() as RegisterResponse ?
} else {
val validationError = t.body() as ValidationError?
//this is also null
println("error resp " + validationError?.message?.password?.get(0))
error.value = t.body() as ValidationError?
}
}
override fun onError(e: Throwable) {}
})
I am trying to get a generic Response as Any and then if the response returns a valid response I cast it to RegisterResponse and if it returns error then I cast it to ValidationError response. But when I am doing this, it is returning null every time. What am I doing wrong here?
Any specifies and assures your instance t is not NULL. The only explanation is that t.body() is null, and that it is a nullable type. There is not enough info here to solve why.
If your are certain it should not be, cast to non-null types
val registerResponse = t.body() as RegisterResponse
val validationError = t.body() as ValidationError
That will make your code much cleaner downstream as well, and you can remove all the null guards.
You will also get an exception instead of falling through.
Related
Looking for a natural Kotlin way to let startTime be initialized only in a particular place and exactly once.
The following naive implementation have two problems:
it is not thread safe
it does not express the fact "the variable was or will be assigned exactly once in the lifetime of an Item instance"
class Item {
var startTime: Instant?
fun start(){
if (startTime == null){
startTime = Instant.now()
}
// do stuff
}
}
I believe some kind of a delegate could be applicable here. In other words this code needs something similar to a lazy variable, but without initialization on first read, instead it happens only after explicit call of "touching" method. Maybe the Wrap calls could give an idea of possible implementation.
class Wrap<T>(
supp: () -> T
){
private var value: T? = null
private val lock = ReentrantLock()
fun get(){
return value
}
fun touch(){
lock.lock()
try{
if (value == null){
value = supp()
} else {
throw IllegalStateExecption("Duplicate init")
}
} finally{
lock.unlock()
}
}
}
How about combining AtomicReference.compareAndSet with a custom backing field?
You can use a private setter and make sure that the only place the class sets the value is from the start() method.
class Item(val value: Int) {
private val _startTime = AtomicReference(Instant.EPOCH)
var startTime: Instant?
get() = _startTime.get().takeIf { it != Instant.EPOCH }
private set(value) = check(_startTime.compareAndSet(Instant.EPOCH, value)) { "Duplicate set" }
fun start() {
startTime = Instant.now()
}
override fun toString() = "$value: $startTime"
}
fun main() = runBlocking {
val item1 = Item(1)
val item2 = Item(2)
println(Instant.now())
launch { println(item1); item1.start(); println(item1) }
launch { println(item1) }
delay(1000)
println(item2)
item2.start()
println(item2)
println(item2)
item2.start()
}
Example output:
2021-07-14T08:20:27.546821Z
1: null
1: 2021-07-14T08:20:27.607365Z
1: 2021-07-14T08:20:27.607365Z
2: null
2: 2021-07-14T08:20:28.584114Z
2: 2021-07-14T08:20:28.584114Z
Exception in thread "main" java.lang.IllegalStateException: Duplicate set
I think your Wrap class is a good starting point to implement this. I would definitely make it a property delegate and touch() could be much simplified:
fun touch() {
synchronized(this) {
check(value == null) { "Duplicate init" }
value = supp()
}
}
Then you can remove lock. But generally, this is a good approach.
If you would like to reuse lazy util from stdlib then you can do this by wrapping it with another object which does not read its value until asked:
class ManualLazy<T : Any>(private val lazy: Lazy<T>) {
operator fun getValue(thisRef: Any?, property: KProperty<*>): T? {
return if (lazy.isInitialized()) lazy.value else null
}
fun touch() {
lazy.value
}
}
class Item {
private val _startTime = ManualLazy(lazy { Instant.now() })
val startTime: Instant? by _startTime
fun start(){
_startTime.touch()
}
}
Of course, depending on your needs you can implement it in a much different way, using a similar technique.
This may be considered exploiting or hacking lazy util. I agree and I think Wrap approach is a better one.
using kotlin, having code
fun fetchRemoteDataApi(): Single<RemoteDataResponse> = networkApi.getData()
// it is just a retrofit
#GET(".../api/getData")
fun getData() : Single<RemoteDataResponse>
fun mergeApiWithDb(): Completable = fetchRemoteDataApi()
.zipWith(localDao.getAll())
.flatMapCompletable { (remoteData, localData) ->
doMerge(remoteData, localData) //<== return a Completable
}
the code flow:
val mergeApiDbCall = mergeApiWithDb().onErrorComplete().cache() //<=== would like do some inspection at this level
PublishSubject.create<Unit>().toFlowable(BackpressureStrategy.LATEST)
.compose(Transformers.flowableIO())
.switchMap {
//merge DB with api, or local default value first then listen to DB change
mergeApiDbCall.andThen(listAllTopics())
.concatMapSingle { topics -> remoteTopicUsers.map { topics to it } }
}
.flatMapCompletable { (topics, user) ->
// do something return Completable
}
.subscribe({
...
}, { throwable ->
...
})
and when making the call
val mergeApiDbCall = mergeApiWithDb().onErrorComplete().cache()
the question is if would like to inspect on the Singles<RemoteDataResponse> returned from fetchRemoteDataApi() (i.e. using Log.i(...) to printout the content of RemoteDataResponse, etc.), either in got error or success case, how to do it?
/// the functions
fun listAllTopics(): Flowable<List<String>> = localRepoDao.getAllTopics()
// which a DAO:
#Query("SELECT topic FROM RemoteDataTable WHERE read = 1")
fun getAllTopics(): Flowable<List<String>>
///
private val remoteTopicUsers: Single<List<User>>
get() {
return Single.create {
networkApi.getTopicUsers(object : ICallback.IGetTopicUsersCallback {
override fun onSuccess(result: List<User>) = it.onSuccess(result)
override fun onError(errorCode: Int, errorMsg: String?) = it.onError(Exception(errorCode, errorMsg))
})
}
}
You cannot extract information about elements from the Completable. Though you can use doOnComplete() on Completable, it will not provide you any information about the element.
You can inspect elements if you call doOnSuccess() on your Single, so you need to incorporate this call earlier in your code. To inspect errors you can use doOnError() on both Completable or Single.
I want to write a Promise class in kotlin. This class uses a generic type. The type can also be a nullable type. When I call the consumer, the value can be null, if the genereic type is nullable. If not the value must be set to an object. The kotlin compiler shows me following message:
Smart cast to 'T' is impossible, because 'value' is a mutable property that could have been changed by this time
I understand why this message appears but I am sure, that the value must be correct at this moment. How can I compile this class? I tried to force to access the value with !! but then my test with null will fail with a NPE.
java.lang.NullPointerException
at test.Promise.resolve(App.kt:20)
at test.AppTest.testPromiseNull(AppTest.kt:31)
class Promise<R> {
private var resolved = false
private var value: R? = null
var then: Consumer<R>? = null
fun resolve(r: R) = synchronized(this) {
if (resolved) error("Promise already resolved!")
value = r
resolved = true
then?.accept(value) // Smart cast to 'T' is impossible, because 'value' is a mutable property that could have been changed by this time*
}
fun then(consumer: Consumer<R>) = synchronized(this) {
if (then != null) error("Just one consumer is allowed!")
then = consumer
val value = value
if (resolved) {
consumer.accept(value) // Smart cast to 'T' is impossible, because 'value' is a mutable property that could have been changed by this time*
}
}
}
#Test fun testPromise() {
val promise = Promise<String>()
var resolved = false
promise.then {
assertEquals(it, "hello" )
resolved = true
}
promise.resolve("hello")
assert(resolved)
}
#Test fun testPromiseNull() {
val promise = Promise<String?>()
var resolved = false
promise.then {
assertNull(it)
resolved = true
}
promise.resolve(null)
assert(resolved)
}
UPDATE
I created a little help function
private fun <T> uncheckedCast(t: T?): T {
#Suppress("UNCHECKED_CAST")
return t as T
}
For your resolve function, you already have the immutable parameter value you can use instead.
fun resolve(r: R) = synchronized(this) {
if (resolved) error("Promise already resolved!")
value = r
resolved = true
then?.accept(r)
}
In the other case, since you know more than the compiler, you can do an explicit cast, and suppress the warning.
fun then(consumer: Consumer<R>) = synchronized(this) {
if (then != null) error("Just one consumer is allowed!")
then = consumer
if (resolved) {
#Suppress("UNCHECKED_CAST")
consumer.accept(value as R)
}
}
I am new to kotlin. I wonder if this is possible
I wish to create a function that will change the value of the properties of the object and return the object itself. The main benefit is that I can chain this setter.
class Person {
var name:String? = null
var age:Int? = null
fun setter(propName:String, value:Any): Person{
return this.apply {
try {
// the line below caused error
this[propName] = value
} catch(e:Exception){
println(e.printStackTrace())
}
}
}
}
//usage
var person = Person(null,null)
person
.setter(name, "Baby")
.setter(age, 20)
But I get error "unknown references"
This question is marked as duplicate, however the possible duplicate question specifically want to change the property of "name", but I wish to change anyProperty that is pass from the function to object. Can't seem to connect the dot between two questions. #Moira Kindly provide answer that explain it. thankyou
Why not just simplify your answer to
fun setter(propName: String, value: Any): Person {
val property = this::class.memberProperties.find { it.name == propName }
when (property) {
is KMutableProperty<*> ->
property.setter.call(this, value)
null ->
// no such property
else ->
// immutable property
}
}
Java reflection isn't needed, its only effect is to stop non-trivial properties from being supported.
Also, if you call it operator fun set instead of fun setter, the
this[propName] = value
syntax can be used to call it.
After googling around, I think I can provide an answer, but relying on java instead of kotlin purely. It will be great if someone can provide a better answer in kotlin.
class Person(
var name: String,
val age: Int
){
fun setter(propName: String, value: Any): Person{
var isFieldExistAndNotFinal = false
try{
val field = this.javaClass.getDeclaredField(propName)
val isFieldFinal = (field.getModifiers() and java.lang.reflect.Modifier.FINAL == java.lang.reflect.Modifier.FINAL)
if(!isFieldFinal) {
// not final
isFieldExistAndNotFinal = true
}
// final variable cannot be changed
else throw ( Exception("field '$propName' is constant, in ${this.toString()}"))
} catch (e: Exception) {
// object does not have property
println("$e in ${this.toString()}")
}
if(isFieldExistAndNotFinal){
val property = this::class.memberProperties.find { it.name == propName }
if (property is KMutableProperty<*>) {
property.setter.call(this, value)
}
}
return this;
}
}
usage like this
person
.setter(propName = "age", value = 30.00)
.setter(propName = "asdf", value = "asdf")
.setter(propName = "name", value = "A Vidy")
You have error because when you do this[propName] = value you are trying to use this as a list, but it is not a list, it is a Person and it doesn't overload the [] operator.
What you can do is to add a check for the property that is setted:
class Person {
privavar name:String? = null
var age:Int? = null
fun setter(propName:String, value:Any): Person{
return this.apply {
if (propName == "name" && value is String?) {
it.name = value as String?
} else if (propName == "age" && value is Int?) {
it.age = value as Int?
} else {
// handle unknown property or value has incorrect type
}
}
}
}
Another more dynamic solution without reflection:
class Person {
private var fields: Map<String, Any?> = HashMap()
fun setter(propName:String, value:Any): Person{
return this.apply {
it.fields[propName] = value;
}
}
fun getName() = fields["name"]
}
If you want to get rid of the getters as well then you need to use reflection.
networkCall = NetworkCall(context)
val responceCall = networkCall!!.getRetrofit(true).callReadMeService()
responceCall.clone().enqueue(object : Callback<BaseResponse<*>?> {
override fun onResponse(call: Call<BaseResponse<*>?>, response: Response<BaseResponse<*>?>) {
networkCall!!.dismissLoading()
web_view!!.loadData((response.body()?.data as LinkedTreeMap<*, *>)["description"] as String, "text/html", "UTF-8")
}
override fun onFailure(call: Call<BaseResponse<*>?>, t: Throwable) {
networkCall!!.dismissLoading()
}
})
here is api method
#POST("stories/readme")
fun callReadMeService(): Call<BaseResponse<*>?>
now i am getting this exception
here is my BaseResponse class
class BaseResponse<T> {
var message: String? = null
var status: Boolean = false
var errors: Array<String>? = null
var code: String? = null
var data: T? = null
}
Method return type must not include a type variable or wildcard: retrofit2.Call>
for method IApi.callReadMeService
now i can't remove generic data variable from BaseResponse class, cause i am using this class as a common Api parser
any solution for this
You cannot do this, because the type info needs to be fully specified, otherwise retrofit cannot correctly generate the Service. See this discussion.
You need to create a different API method for each type.