我正在开发新闻应用程序，并且已经使用进度栏实现了实时数据，但是我的代码中出现了以下异常
java.lang.IllegalStateException: pb must not be null
at yodgorbek.komilov.musobaqayangiliklari.ui.TopHeadlinesFragment$initViewModel$2.onChanged(TopHeadlinesFragment.kt:60)
at yodgorbek.komilov.musobaqayangiliklari.ui.TopHeadlinesFragment$initViewModel$2.onChanged(TopHeadlinesFragment.kt:22)
at androidx.lifecycle.LiveData.considerNotify(LiveData.java:131)
at androidx.lifecycle.LiveData.dispatchingValue(LiveData.java:144)
at androidx.lifecycle.LiveData$ObserverWrapper.activeStateChanged(LiveData.java:442)
at androidx.lifecycle.LiveData$LifecycleBoundObserver.onStateChanged(LiveData.java:394)
at androidx.lifecycle.LifecycleRegistry$ObserverWithState.dispatchEvent(LifecycleRegistry.java:361)
at androidx.lifecycle.LifecycleRegistry.forwardPass(LifecycleRegistry.java:300)
at androidx.lifecycle.LifecycleRegistry.sync(LifecycleRegistry.java:339)
at androidx.lifecycle.LifecycleRegistry.moveToState(LifecycleRegistry.java:145)
at androidx.lifecycle.LifecycleRegistry.handleLifecycleEvent(LifecycleRegistry.java:131)
at androidx.fragment.app.Fragment.performStart(Fragment.java:2637)
at androidx.fragment.app.FragmentManagerImpl.moveToState(FragmentManagerImpl.java:915)
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$2.run(FragmentManagerImpl.java:150)
at android.os.Handler.handleCallback(Handler.java:873)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:201)
at android.app.ActivityThread.main(ActivityThread.java:6820)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:547)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:922)
在我的TopHeadlinesFragment.kt类之下
class TopHeadlinesFragment : Fragment() {
private var binding: FragmentTopHeadlinesBinding? = null
private val viewModel by viewModel<MainViewModel>()
private lateinit var topHeadlinesAdapter: TopHeadlinesAdapter
// private val newsRepository: NewsRepository by inject()
private var article:List<Article>? = 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, article)
recyclerView.layoutManager = LinearLayoutManager(context)
recyclerView.adapter = topHeadlinesAdapter
initViewModel()
binding?.lifecycleOwner
return binding?.root
}
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()
}
}
fragment_top_headlines.xml以下
<androidx.recyclerview.widget.RecyclerView
android:id="@+id/recyclerView"
android:layout_width="0dp"
android:layout_height="wrap_content"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<ProgressBar
android:id="@+id/pb"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>
我已遵循所有stackoverflow的建议，但并没有解决我的问题。我想知道我到底在哪里犯错，为了避免发生异常，我必须做什么。
我尝试过的
1。使缓存重新启动无效2.清理并重建项目3.我检查了进度条是否已经初始化。4.我也尝试了这个stackoverflow链接Android: Progressbar must not be null using Kotlin
在我的MainViewModel.kt下面
@ Suppress（“ UNCHECKED_CAST”）类MainViewModel（val newsRepository：NewsRepository）：ViewModel（），CoroutineScope {//协程的后台工作val job = Job（）//将Coroutine的默认线程定义为Main并添加作业覆盖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()
}
}