我正在开发一个非常简单的示例应用程序,它使用 ViewModel、协程和数据绑定。
这里使用了非常简单的类:
class MainFragment : Fragment() {
companion object {
fun newInstance() = MainFragment()
}
private val viewModel by viewModels<MainViewModel>()
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View {
val binding: MainFragmentBinding =
DataBindingUtil.inflate(inflater, R.layout.main_fragment, container, false)
binding.lifecycleOwner = viewLifecycleOwner
binding.model = viewModel
return binding.root
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
viewModel.loadData()
}
}
class MainViewModel : ViewModel() {
val txt1 = MutableLiveData<String>()
val txt2 = Transformations.map(txt1)
{
if (it == "test") R.string.yes else R.string.no
}
fun loadData() {
viewModelScope.launch(Dispatchers.IO)
{
delay(1000)
txt1.postValue("test")
}
}
}
<?xml version="1.0" encoding="utf-8"?>
<layout>
<data>
<variable
name="model"
type="com.example.myapplication.ui.main.MainViewModel" />
</data>
<androidx.constraintlayout.widget.ConstraintLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/main"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".ui.main.MainFragment">
<TextView
android:id="@+id/txt1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@{model.txt1}"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"/>
<TextView
android:id="@+id/txt2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@{model.txt2}"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"/>
</androidx.constraintlayout.widget.ConstraintLayout>
</layout>
不幸的是,这个非常简单的应用程序因以下堆栈跟踪而崩溃:
java.lang.RuntimeException: Failed to call observer method
at androidx.lifecycle.ClassesInfoCache$MethodReference.invokeCallback(ClassesInfoCache.java:226)
at androidx.lifecycle.ClassesInfoCache$CallbackInfo.invokeMethodsForEvent(ClassesInfoCache.java:194)
at androidx.lifecycle.ClassesInfoCache$CallbackInfo.invokeCallbacks(ClassesInfoCache.java:185)
at androidx.lifecycle.ReflectiveGenericLifecycleObserver.onStateChanged(ReflectiveGenericLifecycleObserver.java:37)
at androidx.lifecycle.LifecycleRegistry$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.FragmentViewLifecycleOwner.handleLifecycleEvent(FragmentViewLifecycleOwner.java:51)
at androidx.fragment.app.Fragment.performStart(Fragment.java:2737)
at androidx.fragment.app.FragmentStateManager.start(FragmentStateManager.java:355)
at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1192)
at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1354)
at androidx.fragment.app.FragmentManager.moveFragmentToExpectedState(FragmentManager.java:1432)
at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1495)
at androidx.fragment.app.FragmentManager.dispatchStateChange(FragmentManager.java:2617)
at androidx.fragment.app.FragmentManager.dispatchStart(FragmentManager.java:2575)
at androidx.fragment.app.FragmentController.dispatchStart(FragmentController.java:258)
at androidx.fragment.app.FragmentActivity.onStart(FragmentActivity.java:550)
at androidx.appcompat.app.AppCompatActivity.onStart(AppCompatActivity.java:178)
at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1391)
at android.app.Activity.performStart(Activity.java:7157)
at android.app.ActivityThread.handleStartActivity(ActivityThread.java:2937)
at android.app.servertransaction.TransactionExecutor.performLifecycleSequence(TransactionExecutor.java:180)
at android.app.servertransaction.TransactionExecutor.cycleToPath(TransactionExecutor.java:165)
at android.app.servertransaction.TransactionExecutor.executeLifecycleState(TransactionExecutor.java:142)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:70)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:6669)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
Caused by: android.content.res.Resources$NotFoundException: String resource ID #0x0
at android.content.res.Resources.getText(Resources.java:348)
at android.widget.TextView.setText(TextView.java:5831)
at com.example.myapplication.databinding.MainFragmentBindingImpl.executeBindings(MainFragmentBindingImpl.java:168)
at androidx.databinding.ViewDataBinding.executeBindingsInternal(ViewDataBinding.java:472)
at androidx.databinding.ViewDataBinding.executePendingBindings(ViewDataBinding.java:444)
at androidx.databinding.ViewDataBinding$OnStartListener.onStart(ViewDataBinding.java:1685)
at java.lang.reflect.Method.invoke(Native Method)
at androidx.lifecycle.ClassesInfoCache$MethodReference.invokeCallback(ClassesInfoCache.java:216)
at androidx.lifecycle.ClassesInfoCache$CallbackInfo.invokeMethodsForEvent(ClassesInfoCache.java:194)
at androidx.lifecycle.ClassesInfoCache$CallbackInfo.invokeCallbacks(ClassesInfoCache.java:185)
at androidx.lifecycle.ReflectiveGenericLifecycleObserver.onStateChanged(ReflectiveGenericLifecycleObserver.java:37)
at androidx.lifecycle.LifecycleRegistry$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.FragmentViewLifecycleOwner.handleLifecycleEvent(FragmentViewLifecycleOwner.java:51)
at androidx.fragment.app.Fragment.performStart(Fragment.java:2737)
at androidx.fragment.app.FragmentStateManager.start(FragmentStateManager.java:355)
at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1192)
at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1354)
at androidx.fragment.app.FragmentManager.moveFragmentToExpectedState(FragmentManager.java:1432)
at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1495)
at androidx.fragment.app.FragmentManager.dispatchStateChange(FragmentManager.java:2617)
at androidx.fragment.app.FragmentManager.dispatchStart(FragmentManager.java:2575)
at androidx.fragment.app.FragmentController.dispatchStart(FragmentController.java:258)
at androidx.fragment.app.FragmentActivity.onStart(FragmentActivity.java:550)
at androidx.appcompat.app.AppCompatActivity.onStart(AppCompatActivity.java:178)
at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1391)
at android.app.Activity.performStart(Activity.java:7157)
at android.app.ActivityThread.handleStartActivity(ActivityThread.java:2937)
at android.app.servertransaction.TransactionExecutor.performLifecycleSequence(TransactionExecutor.java:180)
at android.app.servertransaction.TransactionExecutor.cycleToPath(TransactionExecutor.java:165)
at android.app.servertransaction.TransactionExecutor.executeLifecycleState(TransactionExecutor.java:142)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:70)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:6669)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
MainFragmentBindingImpl.java
该类的第 168 行如下:
this.txt2.setText(androidxDatabindingViewDataBindingSafeUnboxModelTxt2GetValue);
所以,问题是Transformations.map(...)
. 如果我删除txt2
属性的绑定,一切正常。
我怎样才能避免这个错误?
谢谢您的帮助。