I am developing news and I have implemented ViewModel in a fragment. However, my app crashes.
Following is the error I get in my logcat:
java.lang.RuntimeException: Cannot create an instance of class yodgorbek.komilov.musobaqayangiliklari.viewmodel.MainViewModel
at androidx.lifecycle.ViewModelProvider$NewInstanceFactory.create(ViewModelProvider.java:184)
at androidx.lifecycle.ViewModelProvider$AndroidViewModelFactory.create(ViewModelProvider.java:241)
at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.java:164)
at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.java:130)
at yodgorbek.komilov.musobaqayangiliklari.ui.TopHeadlinesFragment.onCreateView(TopHeadlinesFragment.kt:58)
at androidx.fragment.app.Fragment.performCreateView(Fragment.java:2600)
at androidx.fragment.app.FragmentManagerImpl.moveToState(FragmentManagerImpl.java:881)
at androidx.fragment.app.FragmentManagerImpl.moveFragmentToExpectedState(FragmentManagerImpl.java:1238)
at androidx.fragment.app.FragmentManagerImpl.moveToState(FragmentManagerImpl.java:1303)
at androidx.fragment.app.BackStackRecord.executeOps(BackStackRecord.java:439)
at androidx.fragment.app.FragmentManagerImpl.executeOps(FragmentManagerImpl.java:2079)
at androidx.fragment.app.FragmentManagerImpl.executeOpsTogether(FragmentManagerImpl.java:1869)
at androidx.fragment.app.FragmentManagerImpl.removeRedundantOperationsAndExecute(FragmentManagerImpl.java:1824)
at androidx.fragment.app.FragmentManagerImpl.execPendingActions(FragmentManagerImpl.java:1727)
at androidx.fragment.app.FragmentManagerImpl.dispatchStateChange(FragmentManagerImpl.java:2663)
at androidx.fragment.app.FragmentManagerImpl.dispatchActivityCreated(FragmentManagerImpl.java:2613)
at androidx.fragment.app.FragmentController.dispatchActivityCreated(FragmentController.java:246)
at androidx.fragment.app.FragmentActivity.onStart(FragmentActivity.java:542)
at androidx.appcompat.app.AppCompatActivity.onStart(AppCompatActivity.java:201)
at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1425)
at android.app.Activity.performStart(Activity.java:7825)
at android.app.ActivityThread.handleStartActivity(ActivityThread.java:3294)
at android.app.servertransaction.TransactionExecutor.performLifecycleSequence(TransactionExecutor.java:221)
at android.app.servertransaction.TransactionExecutor.cycleToPath(TransactionExecutor.java:201)
at android.app.servertransaction.TransactionExecutor.executeLifecycleState(TransactionExecutor.java:173)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:97)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2016)
at android.os.Handler.dispatchMessage(Handler.java:107)
at android.os.Looper.loop(Looper.java:214)
at android.app.ActivityThread.main(ActivityThread.java:7356)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)
Caused by: java.lang.InstantiationException: java.lang.Class<yodgorbek.komilov.musobaqayangiliklari.viewmodel.MainViewModel> has no zero argument constructor
at java.lang.Class.newInstance(Native Method)
at androidx.lifecycle.ViewModelProvider$NewInstanceFactory.create(ViewModelProvider.java:182)
Below is my MainViewModel.kt
class MainViewModel(newsRepository: NewsRepository) : ViewModel(), CoroutineScope {
// Coroutine's background job
val job = Job()
val sportNewsInterface: SportNewsInterface? = null
// 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) {
sportNewsInterface?.getNews()
}
// 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 is my MainViewModelFactory.kt
class MainViewModelFactory(
private val someParameter: NewsRepository
) : ViewModelProvider.NewInstanceFactory() {
override fun <T : ViewModel> create(modelClass: Class<T>): T {
return MainViewModel(someParameter) as T
}
}
Below is my TopHeadlinesFragment.kt
class TopHeadlinesFragment : Fragment() {
private var viewModel: MainViewModel? = null
private lateinit var topHeadlinesAdapter: TopHeadlinesAdapter
private var newsRepository: NewsRepository? = null
//3
override fun onCreateView(
inflater: LayoutInflater,
container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
val view = inflater.inflate(
R.layout.fragment_top_headlines
, container, false
)
val recyclerView = view.findViewById(R.id.recyclerView) as RecyclerView
val pb = view.findViewById(R.id.pb) as ProgressBar
topHeadlinesAdapter = TopHeadlinesAdapter(recyclerView.context)
recyclerView.layoutManager = LinearLayoutManager(context)
recyclerView.adapter = topHeadlinesAdapter
val param = newsRepository
val factory = param?.let { MainViewModelFactory(it) }
viewModel = ViewModelProviders.of(this, factory).get(MainViewModel::class.java)
initViewModel()
return view
}
private fun initViewModel() {
viewModel?.sportList?.observe(this, Observer { newList ->
topHeadlinesAdapter.updateData(newList)
})
viewModel?.showLoading?.observe(this, Observer { showLoading ->
pb.visibility = if (showLoading) View.VISIBLE else View.GONE
})
viewModel?.showError?.observe(this, Observer { showError ->
(showError)
})
viewModel?.loadNews()
}
}
NewsRepository.kt
interface NewsRepository {
// Suspend is used to await the result from Deferred
suspend fun getNewsList(): UseCaseResult<List<Article>>
}
class NewsRepositoryImpl(private val sportNewsInterface: SportNewsInterface) : NewsRepository {
override suspend fun getNewsList(): UseCaseResult<List<Article>> {
return try {
val result = sportNewsInterface.getNews()
UseCaseResult.Success(result) as UseCaseResult<List<Article>>
} catch (ex: Exception) {
UseCaseResult.Error(ex)
}
}
}
below appModules.kt
const val BASE_URL = "https://newsapi.org/"
val appModules = module {
// The Retrofit service using our custom HTTP client instance as a singleton
single {
createWebService<SportNewsInterface>(
okHttpClient = createHttpClient(),
factory = RxJava2CallAdapterFactory.create(),
baseUrl = BASE_URL
)
}
// Tells Koin how to create an instance of CatRepository
factory<NewsRepository> { (NewsRepositoryImpl(sportNewsInterface = get())) }
// Specific viewModel pattern to tell Koin how to build MainViewModel
viewModel { MainViewModel (newsRepository = get ()) }
}
/* Returns a custom OkHttpClient instance with interceptor. Used for building Retrofit service */
fun createHttpClient(): OkHttpClient {
val client = OkHttpClient.Builder()
client.readTimeout(5 * 60, TimeUnit.SECONDS)
return client.addInterceptor {
val original = it.request()
val requestBuilder = original.newBuilder()
requestBuilder.header("Content-Type", "application/json")
val request = requestBuilder.method(original.method, original.body).build()
return@addInterceptor it.proceed(request)
}.build()
}
/* function to build our Retrofit service */
inline fun <reified T> createWebService(
okHttpClient: OkHttpClient,
factory: CallAdapter.Factory, baseUrl: String
): T {
val retrofit = Retrofit.Builder()
.baseUrl(baseUrl)
.addConverterFactory(GsonConverterFactory.create(GsonBuilder().setLenient().create()))
.addCallAdapterFactory(CoroutineCallAdapterFactory())
.addCallAdapterFactory(factory)
.client(okHttpClient)
.build()
return retrofit.create(T::class.java)
}
Please let me know, how to fix this crash
I have followed a method described here
Your ViewModelFactory needs to have NewsRepository to construct the ViewModel. But you newRepository is not initialized, and hence the factory is not initialized. Check the code again.
Update : OP is using Koin for dependency injection and forgot to inject NewsRepository in the fragement.
Solved by using private val newsRepository: newsRepository by inject()