我想将依赖项 (HomeViewModel) 注入(inject)到我的 fragment (HomeFragment) 中。
我有一个实现该抽象 (HomeViewModel) 的类 (HomeViewModelImpl),在这个类中,我当然会覆盖父类的方法。
抽象类(HomeViewModel)是从BaseViewModel扩展而来的抽象类。
BaseViewModel 是一个普通的 open
类,它从 Android 生命周期组件的 ViewModel 类扩展而来。
问题是当我想将 HomeViewModel
注入(inject) fragment 时出现错误:
> error: [Dagger/MissingBinding] [dagger.android.AndroidInjector.inject(T)] com.example.mvvm.ui.home.HomeViewModel cannot be provided without an @Provides-annotated method.
public abstract interface AppComponent extends dagger.android.AndroidInjector<com.example.mvvm.MyApplication> {
^
com.example.mvvm.ui.home.HomeViewModel is injected at
com.example.mvvm.ui.home.HomeFragment.viewModel
com.example.mvvm.ui.home.HomeFragment is injected at
dagger.android.AndroidInjector.inject(T)
首页 fragment :
class HomeFragment : BaseFragment() {
//Error comes from this line
@Inject
lateinit var viewModel: HomeViewModel
}
HomeViewModel:
//If I write @Inject annotation here, the error goes away,
//but then I have to remove the abstract keyword, then I have to open the class
//and the useful usage of that abstract class in HomeViewModelImpl class
//will be gone, and I have to set open keyword on the HomeViewModel and
//on its method.
/*open*/ abstract class HomeViewModel /*@Inject constructor()*/ : BaseViewModel() {
sealed class State {
data class AlbumsLoaded(val albums: List<AlbumData>) : State()
object ShowLoading : State()
object ShowContent : State()
object ShowError : State()
}
abstract fun fetchAlbums()
}
基础 View 模型:
open class BaseViewModel : ViewModel() {
private val compositeDisposable: CompositeDisposable = CompositeDisposable()
protected fun addDisposable(disposable: Disposable) {
compositeDisposable.add(disposable)
}
private fun clearDisposables() {
compositeDisposable.clear()
}
override fun onCleared() {
clearDisposables()
}
}
家庭模块:
@Module(includes = [
//HomeModule.HomeViewModelProvide::class,
HomeModule.HomeVM::class])
internal abstract class HomeModule {
@ContributesAndroidInjector
internal abstract fun homeFragment(): HomeFragment
@Module
abstract class HomeVM {
@Binds
@IntoMap
@ViewModelKey(HomeViewModelImpl::class)
internal abstract fun bindHomeViewModel(viewModel: HomeViewModelImpl): HomeViewModel
//I've changed the return type of this method from HomeViewModel to
//BaseViewModel and ViewModel, but error still exists!
}
//I've written this to provide HomeViewModel, but compiler shows another error
//that says there is a dependency circle!
/*@Module
class HomeViewModelProvide {
@Provides
internal fun provideHomeViewModel(homeViewModel: HomeViewModel): HomeViewModel = homeViewModel
}*/
}
ViewModelKey:
@Target(AnnotationTarget.FUNCTION, AnnotationTarget.PROPERTY_GETTER, AnnotationTarget.PROPERTY_SETTER)
@Retention(AnnotationRetention.RUNTIME)
@MapKey
annotation class ViewModelKey(val value: KClass<out ViewModel>)
View 模型工厂:
class ViewModelFactory @Inject constructor(
private val creators: @JvmSuppressWildcards Map<Class<out ViewModel>, Provider<ViewModel>>
) : ViewModelProvider.Factory {
override fun <T : ViewModel> create(modelClass: Class<T>): T {
var creator: Provider<out ViewModel>? = creators[modelClass]
if (creator == null) {
for ((key, value) in creators) {
if (modelClass.isAssignableFrom(key)) {
creator = value
break
}
}
}
if (creator == null) {
throw IllegalArgumentException("unknown model class $modelClass")
}
try {
@Suppress("UNCHECKED_CAST")
return creator.get() as T
} catch (e: Exception) {
throw RuntimeException(e)
}
}
}
View 模型模块:
@Module
internal abstract class ViewModelModule {
@Binds
internal abstract fun bindViewModelFactory(factory: ViewModelFactory): ViewModelProvider.Factory
}
基础模块:
@Module
internal abstract class BaseModule {
@ContributesAndroidInjector(modules = [HomeModule::class])
internal abstract fun mainActivity(): MainActivity
}
应用组件:
@Singleton
@Component(modules = [
AndroidSupportInjectionModule::class,
ViewModelModule::class,
AppModule::class,
BaseModule::class
])
interface AppComponent : AndroidInjector<MyApplication> {
@Component.Builder
abstract class Builder : AndroidInjector.Builder<MyApplication>()
}
注意:请阅读上述 fragment 代码的内嵌注释。
我想要的只是将 HomeViewModel
设置为抽象类并将其注入(inject)到我想要的地方。
最佳答案
解决方案是在 child 和真正的 parent 之间创建一个中间抽象类,然后 child 必须从那个中间抽象类扩展。
HomeViewModel 和中间抽象类:
open class HomeViewModel @Inject constructor() : BaseViewModel() {
sealed class State {
data class AlbumsLoaded(val albums: List<AlbumData>) : State()
object ShowLoading : State()
object ShowContent : State()
object ShowError : State()
}
abstract class Implementation : HomeViewModel() {
abstract fun fetchAlbums()
}
}
HomeViewModelImpl:
class HomeViewModelImpl : HomeViewModel.Implementation() {
override fun fetchAlbums() { }
}
首页 fragment :
class HomeFragment : BaseFragment() {
@Inject
lateinit var viewModel: HomeViewModel
}
关于android - 如果没有@Provides 注释的方法,则无法提供该类,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/52448074/