java.lang.ClassCastException: kotlinx.coroutines.CompletableDeferredImpl cannot be cast to java.util.List?

Question

I am developing a new android app but I am getting the following exception

java.lang.ClassCastException: kotlinx.coroutines.CompletableDeferredImpl cannot be cast to java.util.List
    at yodgorbek.komilov.musobaqayangiliklari.viewmodel.MainViewModel$loadNews$1.invokeSuspend(MainViewModel.kt:42)
    at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
    at kotlinx.coroutines.DispatchedTask.run(Dispatched.kt:241)
    at android.os.Handler.handleCallback(Handler.java:873)
    at android.os.Handler.dispatchMessage(Handler.java:99)
    at android.os.Looper.loop(Looper.java:201)
    at android.app.ActivityThread.main(ActivityThread.java:6820)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:547)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:922)

in my MainViewModel.kt

below my MainViewModel.kt

@Suppress("UNCHECKED_CAST")
class MainViewModel(val newsRepository: NewsRepository) : ViewModel(), CoroutineScope {
    // Coroutine's background job
    val job = Job()
    // Define default thread for Coroutine as Main and add job
    override val coroutineContext: CoroutineContext = Dispatchers.Main + job

    val showLoading = MutableLiveData<Boolean>()
    val sportList = MutableLiveData <List<Article>>()
    val showError = SingleLiveEvent<String>()

    fun loadNews() {
        // Show progressBar during the operation on the MAIN (default) thread
        showLoading.value = true
        // launch the Coroutine
        launch {
            // Switching from MAIN to IO thread for API operation
            // Update our data list with the new one from API
            val result = withContext(Dispatchers.IO) {
                newsRepository?.getNewsList()
            }
            // Hide progressBar once the operation is done on the MAIN (default) thread
            showLoading.value = false
            when (result) {

                is UseCaseResult.Success<*> -> {
                    sportList.value = result.data as List<Article>
                }
                is Error -> showError.value = result.message
            }
        }
    }

    override fun onCleared() {
        super.onCleared()
        // Clear our job when the linked activity is destroyed to avoid memory leaks
        job.cancel()
    }
}

below Article.kt

@Entity(tableName = "news_table")
data class Article(@ColumnInfo(name = "author")val author: String,
                   val content: String,
                   val description: String,
                   val publishedAt: String,
                   val source: Source,
                   val title: String,
                   val url: String,
                   val urlToImage: String
)

below SportNewsResponse.kt

data class SportNewsResponse( val articles: List, val status: String, val totalResults: Int )

below UseCaseResult.kt

sealed class UseCaseResult<out T : Any>() {
    class Success<out T : Any>(val data: T) : UseCaseResult<T>()
    class Error(val exception: Throwable) : UseCaseResult<Nothing>()
}

below NewsRepository.kt where I have implemented UserCaseResult

interface NewsRepository {
    // Suspend is used to await 
    suspend fun getNewsList(): UseCaseResult<List<Article>>
}


@Suppress("UNCHECKED_CAST")
class NewsRepositoryImpl(private val sportsNewsApi: SportNewsInterface) : NewsRepository {
    override suspend fun getNewsList(): UseCaseResult<List<Article>> {

        return try {
            val result = sportsNewsApi.getNewsAsync()
            UseCaseResult.Success(result) as UseCaseResult<List<Article>>
        } catch (ex: Exception) {
            UseCaseResult.Error(ex)
        }
    }
}

below my SportNewsInteface.kt

interface SportNewsInterface {

    @GET("v2/top-headlines?country=us&apiKey=da331087e3f3462bb534b3b0917cbee9")
     fun getNewsAsync(): Deferred<SportNewsResponse>

    @GET("/v2/top-headlines?sources=espn&apiKey=da331087e3f3462bb534b3b0917cbee9")
    fun getEspn(): Deferred<List<SportNewsResponse>>

    @GET("/v2/top-headlines?sources=football-italia&apiKey=da331087e3f3462bb534b3b0917cbee9")
    fun getFootballItalia(): Deferred<List<SportNewsResponse>>

    @GET("/v2/top-headlines?sources=bbc-sport&apiKey=da331087e3f3462bb534b3b0917cbee9")
    fun getBBCSport(): Deferred<List<SportNewsResponse>>

below my Response from server

{
    "status": "ok",
    "totalResults": 38,
    "articles": [
        {
            "source": {
                "id": "cnbc",
                "name": "CNBC"
            },
            "author": "Holly Ellyatt",
            "title": "Russia is now not the only pressing issue that NATO has to deal with - CNBC",
            "description": "Heads of state and government are meeting in the U.K. this week for the 70th anniversary of the military alliance NATO.",
            "url": "https://www.cnbc.com/2019/12/02/nato-summit-alliance-has-more-pressing-issues-than-russia-now.html",
            "urlToImage": "https://image.cnbcfm.com/api/v1/image/106272467-1575218599700gettyimages-997112494.jpeg?v=1575218712",
            "publishedAt": "2019-12-02T07:39:00Z",
            "content": "US president Donald Trump is seen during his press conference at the 2018 NATO Summit in Brussels, Belgium on July 12, 2018.\r\nAs heads of state and government meet in the U.K. this week for the 70th anniversary of the military alliance NATO, discussions are l… [+8623 chars]"
        },
        {
            "source": {
                "id": null,
                "name": "Chron.com"
            },
            "author": "Aaron Wilson",
            "title": "Bill O'Brien gets game ball from Deshaun Watson after Texans' win over Patriots - Chron",
            "description": "In an emotional moment, Texans coach Bill O'Brien was presented with the game ball by quarterback Deshaun Watson following a pivotal win over the New England Patriots.",
            "url": "https://www.chron.com/sports/texans/article/Bill-O-Brien-Deshaun-Watson-Texans-Patriots-14874678.php",
            "urlToImage": "https://s.hdnux.com/photos/01/07/23/50/18692664/3/rawImage.jpg",
            "publishedAt": "2019-12-02T06:16:00Z",
            "content": "<ul><li>Houston Texans head coach Bill O'Brien on the sidelines during the fourth quarter of an NFL game against the New England Patriots at NRG Stadium Sunday, Dec. 1, 2019, in Houston.\r\nHouston Texans head coach Bill O'Brien on the sidelines during the four… [+1583 chars]"


        }
    ]
}

Answer 1

Incorrect:

val result = sportsNewsApi.getNewsAsync()

Correct:

val result = sportsNewsApi.getNewsAsync().await()

Answer 2

  val result = sportsNewsApi.getNewsAsync()
  UseCaseResult.Success(result) as UseCaseResult<List<Article>>

That cast is very suspicious since it should work even without it. That means your cast is invalid, causing the error you're seeing.

Answer 3

So you already made some changes Now getNewsAsync must return UseCaseResult not a list of it, since that's what The endpoint is returning. Then you can get the articles inside this object

Answer 4

in NewsRepository in this 2 lines

 val result = sportsNewsApi.getNewsAsync()
 UseCaseResult.Success(result) as UseCaseResult<List<Article>>

you are trying to cast result to UseCaseResult<List<Article>> , but in SportNewsInterface the getNewsAsync() fun returns Deferred<SportNewsResponse> thus you must cast it to UseCaseResult<Deferred<SportNewsResponse>> like this.

UseCaseResult.Success(result) as UseCaseResult<Deferred<SportNewsResponse>>

or if you want to fetch the value use .await() on getNewsAsync() like this

val result = sportsNewsApi.getNewsAsync().await()
 UseCaseResult.Success(result) as UseCaseResult<SportNewsResponse>

don't forget now you should cast result to UseCaseResult<SportNewsResponse> and remove Deferred