android - 尝试使用 Retrofit 发出 get 请求时无法为类 java.lang.Object 创建调用适配器

Question

我在尝试向 NewsApi.org api 发出获取请求时收到以下错误。根据他们的文档，一切似乎都是正确的，我的设置基本上与很多教程和我在 github 上找到的一些示例相同。

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.newsfeed, PID: 12360
    java.lang.IllegalArgumentException: Unable to create call adapter for class java.lang.Object
        for method NewsApi.getBreakingNews
        at retrofit2.ServiceMethod$Builder.methodError(ServiceMethod.java:720)
        at retrofit2.ServiceMethod$Builder.createCallAdapter(ServiceMethod.java:234)
        at retrofit2.ServiceMethod$Builder.build(ServiceMethod.java:160)
        at retrofit2.Retrofit.loadServiceMethod(Retrofit.java:166)
        at retrofit2.Retrofit$1.invoke(Retrofit.java:145)
        at java.lang.reflect.Proxy.invoke(Proxy.java:393)
        at $Proxy1.getBreakingNews(Unknown Source)
        at com.example.newsfeed.data.API.NewsApi$DefaultImpls.getBreakingNews$default(NewsApi.kt:11)
        at com.example.newsfeed.util.NewsPagingSource.load(NewsPagingSource.kt:25)
        at androidx.paging.PageFetcherSnapshot.doInitialLoad(PageFetcherSnapshot.kt:275)
        at androidx.paging.PageFetcherSnapshot$pageEventFlow$1.invokeSuspend(PageFetcherSnapshot.kt:160)
        at androidx.paging.PageFetcherSnapshot$pageEventFlow$1.invoke(PageFetcherSnapshot.kt)
        at androidx.paging.CancelableChannelFlowKt$cancelableChannelFlow$1.invokeSuspend(CancelableChannelFlow.kt:30)
        at androidx.paging.CancelableChannelFlowKt$cancelableChannelFlow$1.invoke(CancelableChannelFlow.kt)
        at androidx.paging.SimpleChannelFlowKt$simpleChannelFlow$1$1$producer$1$1.invokeSuspend(SimpleChannelFlow.kt:57)
        at androidx.paging.SimpleChannelFlowKt$simpleChannelFlow$1$1$producer$1$1.invoke(SimpleChannelFlow.kt)
        at kotlinx.coroutines.intrinsics.UndispatchedKt.startUndispatchedOrReturn(Undispatched.kt:91)
        at kotlinx.coroutines.CoroutineScopeKt.coroutineScope(CoroutineScope.kt:194)
        at androidx.paging.SimpleChannelFlowKt$simpleChannelFlow$1$1$producer$1.invokeSuspend(SimpleChannelFlow.kt:52)
        at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
        at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:106)
        at kotlinx.coroutines.EventLoop.processUnconfinedEvent(EventLoop.common.kt:69)
        at kotlinx.coroutines.internal.DispatchedContinuationKt.resumeCancellableWith(DispatchedContinuation.kt:357)
        at kotlinx.coroutines.intrinsics.CancellableKt.startCoroutineCancellable(Cancellable.kt:30)
        at kotlinx.coroutines.intrinsics.CancellableKt.startCoroutineCancellable$default(Cancellable.kt:27)
        at kotlinx.coroutines.CoroutineStart.invoke(CoroutineStart.kt:110)
        at kotlinx.coroutines.AbstractCoroutine.start(AbstractCoroutine.kt:158)
        at kotlinx.coroutines.BuildersKt__Builders_commonKt.launch(Builders.common.kt:56)
        at kotlinx.coroutines.BuildersKt.launch(Unknown Source)
        at kotlinx.coroutines.BuildersKt__Builders_commonKt.launch$default(Builders.common.kt:49)
        at kotlinx.coroutines.BuildersKt.launch$default(Unknown Source)
        at androidx.lifecycle.BlockRunner.maybeRun(CoroutineLiveData.kt:174)
        at androidx.lifecycle.CoroutineLiveData.onActive(CoroutineLiveData.kt:240)
        at androidx.lifecycle.LiveData.changeActiveCounter(LiveData.java:390)
        at androidx.lifecycle.LiveData$ObserverWrapper.activeStateChanged(LiveData.java:466)
        at androidx.lifecycle.LiveData$LifecycleBoundObserver.onStateChanged(LiveData.java:425)
        at androidx.lifecycle.LifecycleRegistry$ObserverWithState.dispatchEvent(LifecycleRegistry.java:354)
        at androidx.lifecycle.LifecycleRegistry.forwardPass(LifecycleRegistry.java:265)
        at androidx.lifecycle.LifecycleRegistry.sync(LifecycleRegistry.java:307)
        at androidx.lifecycle.LifecycleRegistry.moveToState(LifecycleRegistry.java:148)
        at androidx.lifecycle.LifecycleRegistry.handleLifecycleEvent(LifecycleRegistry.java:134)
        at androidx.fragment.app.FragmentViewLifecycleOwner.handleLifecycleEvent(FragmentViewLifecycleOwner.java:88)
        at androidx.fragment.app.Fragment.performStart(Fragment.java:3028)
        at androidx.fragment.app.FragmentStateManager.start(FragmentStateManager.java:589)
        at androidx.fragment.app.FragmentStateManager.moveToExpectedState(FragmentStateManager.java:300)
        at androidx.fragment.app.FragmentStore.moveToExpectedState(FragmentStore.java:112)
        at androidx.fragment.app.FragmentManager.moveToS

问题似乎出在我的 api 接口(interface)上，但我会分享更多代码以防万一有用。目前我的api接口(interface)如下:

package com.example.newsfeed.data.API

import com.example.newsfeed.data.API.ApiKey.Companion.API_KEY
import com.example.newsfeed.data.models.NewsApiResponse
import retrofit2.http.GET
import retrofit2.http.Query

interface NewsApi {

    @GET("/v2/top-headlines")
    suspend fun getBreakingNews(
        @Query("country")
        country: String = "us",
        @Query("page")
        pageNum: Int = 1,
        @Query("apiKey")
        apiKey: String = API_KEY,
        @Query("pageSize")
        pageSize: Int
    ): NewsApiResponse

}

用于柄注入(inject)的网络模块:

package com.example.newsfeed.di

import com.example.newsfeed.data.API.NewsApi
import com.example.newsfeed.util.Constants.Companion.BASE_URL
import dagger.Module
import dagger.Provides
import dagger.hilt.InstallIn
import dagger.hilt.components.SingletonComponent
import retrofit2.Retrofit
import retrofit2.converter.gson.GsonConverterFactory
import javax.inject.Singleton

@Module
@InstallIn(SingletonComponent::class)
object NetworkModule {

    @Singleton
    @Provides
    fun provideRetrofit(): Retrofit =
        Retrofit.Builder()
            .baseUrl(BASE_URL)
            .addConverterFactory(GsonConverterFactory.create())
            .build()


    @Provides
    @Singleton
    fun provideNewsApi(retrofit: Retrofit): NewsApi =
        retrofit.create(NewsApi::class.java)
}

我的 PagingSource 设置:

package com.example.newsfeed.util

import androidx.paging.PagingSource
import androidx.paging.PagingState
import com.bumptech.glide.load.HttpException
import com.example.newsfeed.data.API.NewsApi
import com.example.newsfeed.data.models.Article
import com.example.newsfeed.util.Constants.Companion.NEWSAPI_STARTING_PAGE_INDEX
import java.io.IOException


class NewsPagingSource(
    private val newsapi: NewsApi
): PagingSource<Int, Article>() {

    override suspend fun load(params: LoadParams<Int>): LoadResult<Int, Article> {
        val position = params.key ?: NEWSAPI_STARTING_PAGE_INDEX

        return try {

            val response = newsapi.getBreakingNews(pageNum = position, pageSize = params.loadSize)
            val articles = response.articles

            LoadResult.Page(
                data = articles,
                prevKey = if (position == NEWSAPI_STARTING_PAGE_INDEX) null else position - 1,
                nextKey = if (articles.isEmpty()) null else position + 1
            )
        } catch (exception: IOException) {
            LoadResult.Error(exception)
        } catch (exception: HttpException) {
            LoadResult.Error(exception)
        }
    }

    override fun getRefreshKey(state: PagingState<Int, Article>): Int? {
        return state.anchorPosition?.let { anchorPosition ->
            state.closestPageToPosition(anchorPosition)?.prevKey?.plus(1)
                ?: state.closestPageToPosition(anchorPosition)?.nextKey?.minus(1)
        }
    }

}

我的存储库:

package com.example.newsfeed.repository

import androidx.lifecycle.asLiveData
import androidx.paging.Pager
import androidx.paging.PagingConfig
import com.example.newsfeed.data.API.NewsApi
import com.example.newsfeed.util.NewsPagingSource
import javax.inject.Inject
import javax.inject.Singleton

@Singleton
class NewsRepository @Inject constructor(
    private val newsApi: NewsApi
) {
    fun getBreakingNews() =
        Pager(
            config = PagingConfig(
                pageSize = 20,
                maxSize = 100,
                enablePlaceholders = false
            ),
            pagingSourceFactory = { NewsPagingSource(newsApi) }
        ).flow.asLiveData()
}

View 模型:

package com.example.newsfeed.viewmodels


import androidx.lifecycle.ViewModel
import com.example.newsfeed.repository.NewsRepository
import dagger.hilt.android.lifecycle.HiltViewModel
import kotlinx.coroutines.CoroutineScope
import javax.inject.Inject

@HiltViewModel
class NewsScreenViewModel @Inject constructor(
    val newsRepository: NewsRepository,
    private val ApplicationScope: CoroutineScope
): ViewModel() {

    val articles = newsRepository.getBreakingNews()

}

fragment :

package com.example.newsfeed.ui

import android.os.Bundle
import android.view.View
import androidx.fragment.app.Fragment
import androidx.fragment.app.viewModels
import com.example.newsfeed.R
import com.example.newsfeed.adapters.NewsArticlesAdapter
import com.example.newsfeed.databinding.FragmentNewsScreenBinding
import com.example.newsfeed.viewmodels.NewsScreenViewModel
import dagger.hilt.android.AndroidEntryPoint

@AndroidEntryPoint
class NewsScreenFragment : Fragment(R.layout.fragment_news_screen) {

    private val viewModel: NewsScreenViewModel by viewModels()

    private var _binding: FragmentNewsScreenBinding? = null
    private val binding get() = _binding!!

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)

        _binding = FragmentNewsScreenBinding.bind(view)

        val adapter = NewsArticlesAdapter()

        binding.apply {
            newsRecyclerView.setHasFixedSize(true)
            newsRecyclerView.adapter = adapter
        }

        viewModel.articles.observe(viewLifecycleOwner) {
            adapter.submitData(viewLifecycleOwner.lifecycle, it)
        }
    }

    override fun onDestroyView() {
        super.onDestroyView()
        _binding = null
    }

}

Answer 1

您正在运行旧版本的 Retrofit，没有协程支持。

要启用对挂起功能的支持，请将Retrofit升级到版本2.6.0或更高版本。