【发布时间】：2021-04-05 21:16:57
【问题描述】：
我是 Kotlin 的新手，我正在尝试使用依赖注入 (dagger.hilt) 创建一个 ViewModel 实例。我收到“无法创建类 CoursesViewModel 的实例”错误，我不知道为什么。你能帮我解决这个问题吗？
CoursesViewModel.kt
class CoursesViewModel @ViewModelInject constructor(
private val courseDao: CourseDao
) : ViewModel() {
}
AppModule.kt
@Module
@InstallIn(ApplicationComponent::class)
object AppModule {
@Provides
@Singleton
fun provideCourseDatabase(
app: Application,
callback: CourseDatabase.Callback
) = Room.databaseBuilder(app, CourseDatabase::class.java, "course_database")
.fallbackToDestructiveMigration()
.addCallback(callback)
.build()
@Provides
fun provideCourseDao(db: CourseDatabase) = db.courseDao()
@Provides
@Singleton
fun provideApplicationScope() = CoroutineScope(SupervisorJob())
}
CourseDatabase.kt
@Database(entities = [Course::class], version = 1)
abstract class CourseDatabase : RoomDatabase() {
// DbSet equivalent
abstract fun courseDao(): CourseDao
// Inner callback class
class Callback @Inject constructor(
private val dbProvider: Provider<CourseDatabase>,
@ApplicationScope
private val applicationScope: CoroutineScope
) : RoomDatabase.Callback(){
override fun onCreate(database: SupportSQLiteDatabase){
super.onCreate(database)
val courseDao = dbProvider.get().courseDao()
applicationScope.launch {
courseDao.insert(Course("my course")
}
}
}
}
CoursesAllFragment.kt
class CoursesAllFragment : Fragment() {
private val viewModel : CoursesViewModel by viewModels()
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
// Inflate the layout for this fragment
val view: View = inflater.inflate(R.layout.fragment_courses_all, container, false)
// Set the recycler view
val recyclerView: RecyclerView = view.findViewById(R.id.lectures_classes_recycler_view)
recyclerView.setHasFixedSize(true)
recyclerView.setLayoutManager(LinearLayoutManager(context))
recyclerView.setAdapter(CoursesAllAdapter(viewModel)) // Line 26. see: logcat
return view
}
}
logcat 输出：
2021-04-05 23:52:33.202 17137-17137/com.something.something E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.something.something, PID: 17137
java.lang.RuntimeException: Cannot create an instance of class com.something.something.Courses.CoursesViewModel
at androidx.lifecycle.ViewModelProvider$NewInstanceFactory.create(ViewModelProvider.java:221)
at androidx.lifecycle.ViewModelProvider$AndroidViewModelFactory.create(ViewModelProvider.java:278)
at androidx.lifecycle.SavedStateViewModelFactory.create(SavedStateViewModelFactory.java:112)
at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.java:185)
at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.java:150)
at androidx.lifecycle.ViewModelLazy.getValue(ViewModelProvider.kt:54)
at androidx.lifecycle.ViewModelLazy.getValue(ViewModelProvider.kt:41)
at com.something.something.Courses.Fragments.CoursesAllFragment.getViewModel(Unknown Source:2)
//In the following line, "CoursesAllFragment.kt:26" is blue, which is where I pass the view model to an RecyclerViewAdapter.
at com.something.something.Courses.Fragments.CoursesAllFragment.onCreateView(CoursesAllFragment.kt:26)
at androidx.fragment.app.Fragment.performCreateView(Fragment.java:2950)
at androidx.fragment.app.FragmentStateManager.createView(FragmentStateManager.java:518)
at androidx.fragment.app.FragmentStateManager.moveToExpectedState(FragmentStateManager.java:277)
at androidx.fragment.app.FragmentManager.executeOpsTogether(FragmentManager.java:2177)
at androidx.fragment.app.FragmentManager.removeRedundantOperationsAndExecute(FragmentManager.java:2088)
at androidx.fragment.app.FragmentManager.execSingleAction(FragmentManager.java:1959)
at androidx.fragment.app.BackStackRecord.commitNowAllowingStateLoss(BackStackRecord.java:306)
at androidx.fragment.app.FragmentPagerAdapter.finishUpdate(FragmentPagerAdapter.java:249)
at androidx.viewpager.widget.ViewPager.populate(ViewPager.java:1244)
at androidx.viewpager.widget.ViewPager.populate(ViewPager.java:1092)
at androidx.viewpager.widget.ViewPager.onMeasure(ViewPager.java:1622)
at android.view.View.measure(View.java:25466)
at androidx.constraintlayout.widget.ConstraintLayout$Measurer.measure(ConstraintLayout.java:792)
at androidx.constraintlayout.solver.widgets.ConstraintWidgetContainer.measure(ConstraintWidgetContainer.java:583)
at androidx.constraintlayout.solver.widgets.ConstraintWidgetContainer.layout(ConstraintWidgetContainer.java:682)
at androidx.constraintlayout.solver.widgets.analyzer.BasicMeasure.solveLinearSystem(BasicMeasure.java:159)
at androidx.constraintlayout.solver.widgets.analyzer.BasicMeasure.solverMeasure(BasicMeasure.java:290)
at androidx.constraintlayout.solver.widgets.ConstraintWidgetContainer.measure(ConstraintWidgetContainer.java:119)
at androidx.constraintlayout.widget.ConstraintLayout.resolveSystem(ConstraintLayout.java:1578)
at androidx.constraintlayout.widget.ConstraintLayout.onMeasure(ConstraintLayout.java:1690)
at android.view.View.measure(View.java:25466)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6957)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at android.view.View.measure(View.java:25466)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6957)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at android.view.View.measure(View.java:25466)
at androidx.constraintlayout.widget.ConstraintLayout$Measurer.measure(ConstraintLayout.java:792)
at androidx.constraintlayout.solver.widgets.ConstraintWidgetContainer.measure(ConstraintWidgetContainer.java:583)
at androidx.constraintlayout.solver.widgets.analyzer.Direct.verticalSolvingPass(Direct.java:355)
at androidx.constraintlayout.solver.widgets.analyzer.Direct.solveVerticalMatchConstraint(Direct.java:636)
at androidx.constraintlayout.solver.widgets.analyzer.Direct.verticalSolvingPass(Direct.java:407)
at androidx.constraintlayout.solver.widgets.analyzer.Direct.solvingPass(Direct.java:178)
at androidx.constraintlayout.solver.widgets.ConstraintWidgetContainer.layout(ConstraintWidgetContainer.java:642)
at androidx.constraintlayout.solver.widgets.analyzer.BasicMeasure.solveLinearSystem(BasicMeasure.java:159)
2021-04-05 23:52:33.202 17137-17137/com.something.something E/AndroidRuntime: at androidx.constraintlayout.solver.widgets.analyzer.BasicMeasure.solverMeasure(BasicMeasure.java:290)
at androidx.constraintlayout.solver.widgets.ConstraintWidgetContainer.measure(ConstraintWidgetContainer.java:119)
at androidx.constraintlayout.widget.ConstraintLayout.resolveSystem(ConstraintLayout.java:1578)
at androidx.constraintlayout.widget.ConstraintLayout.onMeasure(ConstraintLayout.java:1690)
at android.view.View.measure(View.java:25466)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6957)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at android.view.View.measure(View.java:25466)
at androidx.constraintlayout.widget.ConstraintLayout$Measurer.measure(ConstraintLayout.java:792)
at androidx.constraintlayout.solver.widgets.ConstraintWidgetContainer.measure(ConstraintWidgetContainer.java:583)
at androidx.constraintlayout.solver.widgets.analyzer.Direct.verticalSolvingPass(Direct.java:355)
at androidx.constraintlayout.solver.widgets.analyzer.Direct.solveVerticalMatchConstraint(Direct.java:636)
at androidx.constraintlayout.solver.widgets.analyzer.Direct.verticalSolvingPass(Direct.java:455)
at androidx.constraintlayout.solver.widgets.analyzer.Direct.verticalSolvingPass(Direct.java:387)
at androidx.constraintlayout.solver.widgets.analyzer.Direct.solvingPass(Direct.java:178)
at androidx.constraintlayout.solver.widgets.ConstraintWidgetContainer.layout(ConstraintWidgetContainer.java:642)
at androidx.constraintlayout.solver.widgets.analyzer.BasicMeasure.solveLinearSystem(BasicMeasure.java:159)
at androidx.constraintlayout.solver.widgets.analyzer.BasicMeasure.solverMeasure(BasicMeasure.java:290)
at androidx.constraintlayout.solver.widgets.ConstraintWidgetContainer.measure(ConstraintWidgetContainer.java:119)
at androidx.constraintlayout.widget.ConstraintLayout.resolveSystem(ConstraintLayout.java:1578)
at androidx.constraintlayout.widget.ConstraintLayout.onMeasure(ConstraintLayout.java:1690)
at android.view.View.measure(View.java:25466)
at androidx.drawerlayout.widget.DrawerLayout.onMeasure(DrawerLayout.java:1156)
at android.view.View.measure(View.java:25466)
at androidx.constraintlayout.widget.ConstraintLayout$Measurer.measure(ConstraintLayout.java:792)
at androidx.constraintlayout.solver.widgets.ConstraintWidgetContainer.measure(ConstraintWidgetContainer.java:583)
at androidx.constraintlayout.solver.widgets.analyzer.Direct.verticalSolvingPass(Direct.java:355)
at androidx.constraintlayout.solver.widgets.analyzer.Direct.solveVerticalMatchConstraint(Direct.java:636)
at androidx.constraintlayout.solver.widgets.analyzer.Direct.verticalSolvingPass(Direct.java:407)
at androidx.constraintlayout.solver.widgets.analyzer.Direct.verticalSolvingPass(Direct.java:446)
at androidx.constraintlayout.solver.widgets.analyzer.Direct.solvingPass(Direct.java:178)
at androidx.constraintlayout.solver.widgets.ConstraintWidgetContainer.layout(ConstraintWidgetContainer.java:642)
at androidx.constraintlayout.solver.widgets.analyzer.BasicMeasure.solveLinearSystem(BasicMeasure.java:159)
由于问题正文中的代码过多，Stackoverflow 不允许我粘贴 logcat 输出的其余部分。
【问题讨论】：
-
CoursesAllFragment缺少@AndroidEntryPoint，但无论如何您也应该将您的 Hilt 更新到最新版本，您的版本大约是 2.28-alpha 左右，当前是 2.33-beta。 -
@EpicPandaForce 你的建议解决了它。添加这个作为答案。