Question

我正在开发一个新的android应用程序，但出现以下异常

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)

在我的MainViewModel.kt

在我的MainViewModel.kt下面

@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()
    }
}

Article.kt以下

@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
)

SportNewsResponse.kt以下

数据类SportNewsResponse（ val文章：列表， val状态：字符串， val totalResults：Int ）

在UseCaseResult.kt下面

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

在我实现了UserCaseResult的NewsRepository.kt下面

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)
        }
    }
}

在我的SportNewsInteface.kt下

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>>

在我的服务器回应下方

{
    "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

不正确：

val result = sportsNewsApi.getNewsAsync()

正确：

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

Answer 2

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

该演员阵容非常可疑，因为即使没有演员也可以使用。这意味着您的演员表无效，从而导致您看到的错误。

Answer 3

因此您已经进行了一些更改现在，getNewsAsync必须返回UseCaseResult而不是它的列表，因为这是端点返回的内容。然后，您可以在该对象中获取文章

Answer 4

在NewsRepository中在这2行中

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

您正在尝试将result投射到UseCaseResult<List<Article>> ，但是在SportNewsInterface中，getNewsAsync()会返回Deferred<SportNewsResponse>，因此您必须像这样将其强制转换为UseCaseResult<Deferred<SportNewsResponse>>。

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

或者如果您想获取值，请像这样在.await()上使用getNewsAsync()

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

现在不要忘记，您应该将结果投射到UseCaseResult<SportNewsResponse>并删除Deferred

java.lang.ClassCastException：kotlinx.coroutines.CompletableDeferredImpl无法转换为java.util.List吗？

4 个答案: