Develop Reference

No exception/error when no internet coroutine + retrofit

I have the following setup
Service
// ItunesService
suspend fun searchItunesPodcast(#Query("term") term: String): Response<PodcastResponse>
Repository
// ItunesRepo
override suspend fun searchByTerm(term: String) = withContext(ioDispatcher) {
return#withContext itunesService.searchItunesPodcast(term)
}
ViewModel
fun searchPodcasts(term: String) {
viewModelScope.launch {
_res.value = Result.loading()
try {
val response = itunesRepo.searchByTerm(term)
if (response.isSuccessful) { // Nothing from here when no internet
_res.value = Result.success(response.body())
} else {
_res.value = Result.error(response.errorBody().toString())
}
} catch (e: Exception) {
_res.value = Result.exception(e)
}
}
}
Everything works great until i turn off mobile data/internet on my testing device. _res value stuck on Loading state. I have tried adding break point at if (response.isSuccessful) when there is no internet and it seams like val response = itunesRepo.searchByTerm(term) never returns how can I fix this

I switched to using Flow api on my Repository
override suspend fun searchPodcasts(term: String) = flow {
emit(Result.Loading)
try {
val res = itunesService.searchItunesPodcast(term)
if (res.isSuccessful)
emit(Result.Success(res.body()))
else
emit(Result.Error("Generic error: ${res.code()}"))
} catch (e: Exception) {
emit(Result.Error("Unexpected error", e))
}
}.flowOn(ioDispatcher)
Then collect the results on my ViewModels

how can i wrap this (AdsWizz) Kotlin callback function in a couroutine?

I'm new to coroutines and having a hard time figuring out how to correctly wrap an existing callback in a coroutine.
My goal is to be able to do the following:
lifecycleScope.launch {
withContext(Dispatchers.Main) {
val theResult = getPreRollAd() //1. call this suspending func and wait for result
doSomethingWithResult(theResult) //2. now that the result is returned from AdsWizz API (below), do something with it
}
}
Here is the AdsWizz API call that I'd like to "wrap":
val adReqInterface: AdRequestHandlerInterface = object :
AdRequestHandlerInterface {
override fun onResponseError(error: AdswizzSDKError) {
Timber.e("onResponseError $error")
}
override fun onResponseReady(adResponse: AdResponse) {
Timber.d( "onResponseReadySingleAd")
//this contains the url to the ad, title, etc..
!!!*** I WANT TO RETURN THE adResponse.mediaFile?.source string back to "theResult" variable above (in lifecycleScope.launch {.... )
}
}
try {
AdswizzSDK.getAdsLoader().requestAd(adReqParams, adReqInterface)
} catch (e: IllegalArgumentException) {
Timber.d( "IllegalArgumentException")
} catch (e: SecurityException) {
Timber.d( "SecurityException")
} catch (e: Exception) {
Timber.d( "other exception")
e.printStackTrace()
}
I've tried using suspendCoroutine {... to wrap but nothing is working. Really appreciate someones help re the right way to achieve this.

the right way to do it is to use suspendCancellableCoroutine. It can return a result or can be cancelled with an exception.
suspend fun getPreRollAd(): AdResponse {
return suspendCancellableCoroutine {
...
val adReqInterface: AdRequestHandlerInterface = object : AdRequestHandlerInterface {
override fun onResponseError(error: AdswizzSDKError) {
Timber.e("onResponseError $error")
it.cancel(error)
}
override fun onResponseReady(adResponse: AdResponse) {
Timber.d( "onResponseReadySingleAd")
it.resume(adResponse)
}
}
AdswizzSDK.getAdsLoader().requestAd(adReqParams, adReqInterface)
}
}
viewModelScope.launch {
val result = try {
getPreRollAd()
} catch(e: Throwable) {
null
}
...
}

Generics and MutableLiveData in Kotlin

I have two quite similar functions and I'm trying to avoid duplication in my code by the use of generics. The functions have both a try catch block and notify its observers with two MutableLiveData of two different types:
val noWasteRecipesPosts: MutableLiveData<List<Recipe>> = MutableLiveData()
val lastArticlesPosts: MutableLiveData<List<Article>> = MutableLiveData()
fun getNoWasteRecipesPosts() {
makeCall(service.getRecipes(), noWasteRecipesPosts)
scope.launch {
try {
val response = service.getRecipes().await()
when (response.isSuccessful) {
true -> {
response.body()?.let {
noWasteRecipesPosts.postValue(ArrayList(response.body()))
} ?: run {
errorLiveData.postValue(response.message())
}
}
false -> errorLiveData.postValue(response.message())
}
} catch (e: Exception) {
noConnectionLiveData.postValue(true)
}
}
}
fun getLastArticlesPosts(excludeRecipes: Boolean) {
scope.launch {
try {
val response = when (excludeRecipes) {
true -> service.getLastArticles(categoriesToExclude = arrayListOf(BlogCategories.NO_WASTE_RECIPES.id))
.await()
false -> service.getLastArticles()
.await()
}
when (response.isSuccessful) {
true -> {
response.body()?.let {
lastArticlesPosts.postValue(ArrayList(response.body()))
} ?: run {
errorLiveData.postValue(response.message())
}
}
false -> errorLiveData.postValue(response.message())
}
} catch (e: Exception) {
noConnectionLiveData.postValue(true)
}
}
}
To avoid code repeating I'm trying to use generics, but probably in the wrong way. I've defined a function that takes the Deferred api response as first parameter and I would like to pass a MutableLiveData to notify observers as the second parameter:
fun makeCall(function: Deferred<Response<*>>, successLiveData: MutableLiveData<*>) {
scope.launch {
try {
val response = function.await()
when (response.isSuccessful) {
true -> {
response.body()?.let {
successLiveData.postValue(it) // Compile error here
} ?: run {
errorLiveData.postValue(response.message())
}
}
false -> errorLiveData.postValue(response.message())
}
} catch (e: Exception) {
noConnectionLiveData.postValue(true)
}
}
}
Unfortunately I'm missing something and the IDE is giving me a Type mismatch error trying to post the LiveData value:
Type mismatch: Required : Nothing! Found: Any.
I'm quite confused, do you have any suggestion to make about MutableLiveData and Generics in kotlin?

The response.body() type and the MutableLiveData type must match. The function signature should be something like this:
fun <T> makeCall(function: Deferred<Response<T>>, successLiveData: MutableLiveData<T>)

Handle no internet connection error of retrofit 2.6 with kotlin coroutines

I'm using retrofit 2.6 with kotlin coroutines to make API call without block the UI thread, I got it work but the app crashes when I switch off the internet connection. The logcat error is: E/AndroidRuntime: FATAL EXCEPTION: DefaultDispatcher-worker-1
Here is my code:
private fun handleIntent(slug: String) {
val service = UtilityMethods.migrationTimeService()
UtilityMethods.showView(loading_view)
UtilityMethods.hideView(network_error_msg)
CoroutineScope(Dispatchers.IO).launch {
val res = service.getPostBySlug(slug)
try {
withContext(Dispatchers.Main) {
//Do something with response e.g show to the UI.
val post = res.body()!!.first()
UtilityMethods.hideView(loading_view)
val title = post.title?.rendered
val content = post.content?.rendered
val imageUrl = post.jetPackFeaturedMediaUrl
title_txtView.text = if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N)
Html.fromHtml(title, Html.FROM_HTML_MODE_COMPACT).toString()
else
Html.fromHtml(title).toString()
content_txtView.loadData(content.toString(), "text/html", "UTF-8")
Picasso.get().load(imageUrl).fit().centerCrop().into(thumbnail_imgview)
}
} catch (e: HttpException) {
UtilityMethods.showView(network_error_msg)
} catch (e: Throwable) {
Toast.makeText(this#PostContentActivity, "Ooops: Something else went wrong", Toast.LENGTH_LONG)
}
}
}

I've got the code working, the new code is:
private fun handleIntent(slug: String) = GlobalScope.launch(Dispatchers.Main) {
val service = UtilityMethods.migrationTimeService()
UtilityMethods.showView(loading_view)
UtilityMethods.hideView(network_error_msg)
try {
val res = withContext(Dispatchers.IO) {
service.getPostBySlug(slug)
}
//Do something with response e.g show to the UI.
val post = res.body()!!.first()
UtilityMethods.hideView(loading_view)
val title = post.title?.rendered
val content = post.content?.rendered
val imageUrl = post.jetPackFeaturedMediaUrl
title_txtView.text = if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N)
Html.fromHtml(title, Html.FROM_HTML_MODE_COMPACT).toString()
else
Html.fromHtml(title).toString()
content_txtView.loadData(content.toString(), "text/html", "UTF-8")
Picasso.get().load(imageUrl).fit().centerCrop().into(thumbnail_imgview)
}
catch (e: HttpException) {
Toast.makeText(this#PostContentActivity, "Exception ${e.message}", Toast.LENGTH_LONG).show()
}catch (e: IOException) {
UtilityMethods.hideView(loading_view)
UtilityMethods.showView(network_error_msg)
} catch (e: Throwable) {
Toast.makeText(this#PostContentActivity, "Ooops: Something else went wrong ${e.message}", Toast.LENGTH_LONG).show()
}
}

So while looking into stacktrace I found that ConnectException is thrown when network is unavailable
And that's how I do it in kotlin and it works for me,
suspend fun<T: Any> safeAPICall(call: suspend () -> Response<T>) : T{
val response = try {
call.invoke()
}
catch (e:java.lang.Exception){
e.printStackTrace()
val message = if( e is ConnectException) "Connection Error" else "Something went wrong. Please try again."
throw IOException(ResponseError(message, 500).convertToJsonString())
}
// When connection is OK
if(response.isSuccessful){
return response.body()!!
}else{
val error = response.errorBody()?.string()
error?.let{
val message = JSONObject(it).optString("message", "Something went wrong")
val responseError = ResponseError(message, response.code())
throw IOException(responseError.convertToJsonString())
}
throw IOException(ResponseError("Something went wrong. Please try again.", 500).convertToJsonString())
}
}
The data class that I use
data class ResponseError(val message:String, val errorCode:Int)
Usage:
try {
val response = safeAPICall {APIClient.planner.viewSites(view.context.authToken)}
}
catch (e:Exception){
view.snack(e.message?.toModel<ResponseError>()?.message?: unspecified_error)
}
Bonus:
inline fun <reified T> JSONObject.toModel(): T? = this.run {
try {
Gson().fromJson<T>(this.toString(), T::class.java)
}
catch (e:java.lang.Exception){ e.printStackTrace(); null }
}
inline fun <reified T> String.toModel(): T? = this.run {
try {
JSONObject(this).toModel<T>()
}
catch (e:java.lang.Exception){ null }
}

Instead of this:
CoroutineScope(Dispatchers.IO).launch {
val res = service.getPostBySlug(slug)
try {
withContext(Dispatchers.Main) {
Try this one:
CoroutineScope(Dispatchers.Main).launch {
val res = service.getPostBySlug(slug)
withContext(Dispatchers.IO) {
try {
wrap your 'try and catch' block code within Dispatchers.IO instead of wraping your Dispatchers.IO with in yout try block

How to get the response of another observable when error occurs?

I just want to ask if it is possible to get the response of another observable after encountering an error from the another observable?
for example I am calling a two api Avatar and Attachment using a combineLatest.
val avatar: Observable<ResponseBody> = api().getAvatar()
val attachment: Observable<ResponseBody> = api().getAttachment()
val obs = Observables.combineLatest(avatar, attachment)
.map { it ->
if (it.first is Exception) {
Log.e(TAG, "getAvatar failed")
} else {
updateAvatar()
}
if (it.second is Exception) {
Log.e(TAG, "getAttachment failed")
} else {
updateAttachment()
}
if (it.first !is Exception && it.second !is Exception) {
Log.i(TAG, "success first=${it.first}, second=${it.second}")
updateAll()
}
}
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
.onErrorReturn { it }
.subscribe()
disposable.add(obs)
I just want to get the avatar response if the attachment error and I want to get the attachment response if the avatar error.
Thanks.

Yes, my friend. You can handle error for each observable that you combine by calling onErrorReturn() method. You can use empty ResponseBody for detecting error. Final code
val avatar: Observable<Optional<ResponseBody>> = api().getAvatar().onErrorReturn{ Optional.empty }
val attachment: Observable<Optional<ResponseBody>> = api().getAttachment().onErrorReturn{ Optional.empty }
val obs = Observables.combineLatest(avatar, attachment) {avatar, attachment ->
if (!avatar.isPresent()) {
//logic
}
if (!attachment.isPresent()) {
//logic
}
}.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
.onErrorReturn { it }
.subscribe()
If you use java 7 or lower in you project, you can write your own Optional
class Optional<T>(val value: T?) {
companion object {
fun <T> empty(): Optional<T> = Optional(null)
}
fun isPresent() = value != null
}