我正在开发新闻，并且已经在片段类中实现了viewmodel，但是我运行的代码是从片段类中获取以下异常
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:38)
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$NewInstanceFactory.create(ViewModelProvider.java:182)
at androidx.lifecycle.ViewModelProvider$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:38)
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)
在我遇到异常的TopHeadlinesFragment下方
class TopHeadlinesFragment : Fragment() {
lateinit var viewModel: MainViewModel
var topHeadlinesAdapter: TopHeadlinesAdapter? = null
val showError = SingleLiveEvent<String>()
//3
override fun onCreateView(
inflater: LayoutInflater,
container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
val view = inflater.inflate(
R.layout.fragment_top_headlines
, container, false
)
viewModel = ViewModelProviders.of(this).get(MainViewModel::class.java)
val recyclerView = view.findViewById(R.id.recyclerView) as RecyclerView
val pb = view.findViewById(R.id.pb) as ProgressBar
return view
viewModel.loadNews(viewLifecycleOwner, Observer { result ->
when (result) {
is UseCaseResult.Success<*> -> {
pb.visibility = View.GONE
result.data as List<Deferred<SportNewsResponse>>
topHeadlinesAdapter?.articleList
}
is Error -> {
showError.value = result.message
pb.visibility = View.GONE
}
}
})
}
}
在MainViewModel.kt下面，其中我已实现ViewModel
class MainViewModel(
private val sportNewsInterface: SportNewsInterface
) : ViewModel(), CoroutineScope {
// Coroutine's background job
private val job = Job()
// Define default thread for Coroutine as Main and add job
override val coroutineContext: CoroutineContext = Dispatchers.Main + job
private val showLoading = MutableLiveData<Boolean>()
private val sportList = MutableLiveData<List<Deferred<SportNewsResponse>>>()
val showError = SingleLiveEvent<String>()
fun loadNews(
viewLifecycleOwner: LifecycleOwner,
observer: Observer<Any>
) {
// 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<Deferred<SportNewsResponse>>
}
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()
}
}
NewsRepository.kt以下
interface NewsRepository {
// Suspend is used to await the result from Deferred
suspend fun getNewsList(): UseCaseResult<Deferred<List<SportNewsResponse>>>
}
class NewsRepositoryImpl(private val sportNewsInterface: SportNewsInterface) : NewsRepository {
override suspend fun getNewsList(): UseCaseResult<Deferred<List<SportNewsResponse>>> {
/*
We try to return a list of cats from the API
Await the result from web service and then return it, catching any error from API
*/
return try {
val result = sportNewsInterface.getNews()
UseCaseResult.Success(result) as UseCaseResult<Deferred<List<SportNewsResponse>>>
} catch (ex: Exception) {
UseCaseResult.Error(ex)
}
}
}
在UseCaseResult.kt下面
sealed class UseCaseResult<out T : Any>() {
class Success<out T : Any>(val data: T) : UseCaseResult<List<SportNewsResponse>>()
class Error(val exception: Throwable) : UseCaseResult<Nothing>()
}
在app.gradle下面
apply plugin: 'com.android.application'
apply plugin: 'kotlin-android'
apply plugin: 'kotlin-kapt'
apply plugin: 'kotlin-android-extensions'
android {
compileSdkVersion 29
buildToolsVersion "29.0.2"
defaultConfig {
applicationId "yodgorbek.komilov.musobaqayangiliklari"
minSdkVersion 15
targetSdkVersion 29
versionCode 1
versionName "1.0"
testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
dataBinding {
enabled = true
}
}
buildTypes {
release {
minifyEnabled false
proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
}
}
compileOptions {
sourceCompatibility JavaVersion.VERSION_1_8
targetCompatibility JavaVersion.VERSION_1_8
}
kotlinOptions {
jvmTarget = "1.8"
}
}
dependencies {
implementation fileTree(dir: 'libs', include: ['*.jar'])
implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version"
implementation 'androidx.appcompat:appcompat:1.1.0'
implementation 'androidx.core:core-ktx:1.0.2'
implementation 'androidx.constraintlayout:constraintlayout:1.1.3'
implementation 'com.squareup.retrofit2:retrofit:2.5.0'
implementation 'com.squareup.retrofit2:converter-gson:2.5.0'
implementation 'com.google.code.gson:gson:2.8.5'
implementation 'org.koin:koin-android-viewmodel:1.0.0-RC-1'
implementation 'org.koin:koin-android:0.9.3'
def lifecycle_version = "2.1.0"
implementation 'org.jetbrains.kotlinx:kotlinx-coroutines-android:1.0.1'
implementation 'org.jetbrains.kotlinx:kotlinx-coroutines-core:1.2.0'
implementation "org.koin:koin-androidx-viewmodel:2.0.1"
implementation 'com.jakewharton.retrofit:retrofit2-kotlin-coroutines-adapter:0.9.2'
implementation 'com.squareup.retrofit2:adapter-rxjava2:2.3.0'
// ViewModel and LiveData
implementation "androidx.lifecycle:lifecycle-extensions:$lifecycle_version"
// alternatively - just ViewModel
implementation "androidx.lifecycle:lifecycle-viewmodel:$lifecycle_version"
// For Kotlin use lifecycle-viewmodel-ktx
// alternatively - just LiveData
implementation "androidx.lifecycle:lifecycle-livedata:$lifecycle_version"
// alternatively - Lifecycles only (no ViewModel or LiveData). Some UI
// AndroidX libraries use this lightweight import for Lifecycle
implementation "androidx.lifecycle:lifecycle-runtime:$lifecycle_version"
annotationProcessor "androidx.lifecycle:lifecycle-compiler:$lifecycle_version"
// For Kotlin use kapt instead of annotationProcessor
// alternately - if using Java8, use the following instead of lifecycle-compiler
implementation "androidx.lifecycle:lifecycle-common-java8:$lifecycle_version"
// optional - ReactiveStreams support for LiveData
implementation "androidx.lifecycle:lifecycle-reactivestreams:$lifecycle_version"
// For Kotlin use lifecycle-reactivestreams-ktx
implementation 'com.google.android.material:material:1.0.0'
implementation 'androidx.cardview:cardview:1.0.0'
implementation 'androidx.recyclerview:recyclerview:1.0.0'
implementation 'com.github.bumptech.glide:glide:4.8.0'
// optional - Test helpers for LiveData
testImplementation "androidx.arch.core:core-testing:$lifecycle_version"
implementation 'com.squareup.picasso:picasso:2.71828'
implementation 'com.google.android.material:material:1.0.0-alpha3'
implementation 'com.github.florent37:shapeofview:1.3.2'
implementation 'com.github.AppIntro:AppIntro:5.1.0'
implementation 'androidx.cardview:cardview:1.0.0'
testImplementation 'junit:junit:4.12'
androidTestImplementation 'androidx.test:runner:1.1.1'
androidTestImplementation 'androidx.test.espresso:espresso-core:3.1.1'
implementation 'com.squareup.okhttp3:okhttp:4.2.1'
implementation "com.squareup.okhttp3:logging-interceptor:4.2.1"
def room_version = "2.2.1"
implementation "androidx.room:room-runtime:$room_version"
annotationProcessor "androidx.room:room-compiler:$room_version" // For Kotlin use kapt instead of annotationProcessor
// optional - Kotlin Extensions and Coroutines support for Room
implementation "androidx.room:room-ktx:$room_version"
// Core library
androidTestImplementation 'androidx.test:core:1.0.0'
// AndroidJUnitRunner and JUnit Rules
androidTestImplementation 'androidx.test:runner:1.1.0'
androidTestImplementation 'androidx.test:rules:1.1.0'
// Assertions
androidTestImplementation 'androidx.test.ext:junit:1.0.0'
androidTestImplementation 'androidx.test.ext:truth:1.0.0'
androidTestImplementation 'com.google.truth:truth:0.42'
// Espresso dependencies
androidTestImplementation 'androidx.test.espresso:espresso-core:3.1.0'
androidTestImplementation 'androidx.test.espresso:espresso-contrib:3.1.0'
androidTestImplementation 'androidx.test.espresso:espresso-intents:3.1.0'
androidTestImplementation 'androidx.test.espresso:espresso-accessibility:3.1.0'
androidTestImplementation 'androidx.test.espresso:espresso-web:3.1.0'
androidTestImplementation 'androidx.test.espresso.idling:idling-concurrent:3.1.0'
androidTestImplementation 'com.agoda.kakao:kakao:2.2.0'
androidTestImplementation 'com.21buttons:fragment-test-rule:2.0.1'
debugImplementation 'com.21buttons:fragment-test-rule-extras:2.0.1'
androidTestImplementation 'androidx.test.espresso:espresso-idling-resource:3.1.0'
implementation 'com.github.bumptech.glide:glide:4.10.0'
annotationProcessor 'com.github.bumptech.glide:compiler:4.10.0'
}
在自定义ViewModelParameterizedProvider.kt下面
类ViewModelParameterizedProvider {
companion object {
lateinit var provider: ViewModelProvider
private var viewModelStore: ViewModelStore? = null
fun of(fragment: Fragment): Companion {
viewModelStore = ViewModelStores.of(fragment)
return this@Companion
}
fun of(fragment: android.app.Fragment): Companion {
val fragAct: FragmentActivity = fragment.activity as FragmentActivity;
return of(fragAct)
}
fun of(activity: FragmentActivity): Companion {
viewModelStore = ViewModelStores.of(activity)
return this@Companion
}
fun with(constructorParams: Array<out Any>) =
viewModelStore?.let { ViewModelProvider(it, parametrizedFactory(constructorParams)) }
private fun parametrizedFactory(constructorParams: Array<out Any>) = ParametrizedFactory(constructorParams)
}
class ParametrizedFactory(private var constructorParams: Array<out Any>) : ViewModelProvider.Factory {
override fun <T : ViewModel?> create(modelClass: Class<T>): T {
if (modelClass == null) {
throw IllegalArgumentException("Target ViewModel class can not be null")
}
Log.w("ParametrizedFactory", "Don't use callbacks or Context as parameters in order to avoid leaks!!")
return when (constructorParams.size) {
0 -> {
modelClass.newInstance()
}
else -> {
val parameterClasses: Array<Class<*>> = constructorParams.map { param -> param.javaClass }.toList().toTypedArray()
modelClass.getConstructor(*parameterClasses).newInstance(*constructorParams)
}
}
}
}
}