我有以下课程：
视图模型
class MealPlanViewModel @AssistedInject constructor(private val mealPlanRepository: MealPlanRepository, @Assisted private val canteenId: String) : ViewModel() {
// AssistedInject code for using ViewModel injection with runtime parameters
@AssistedInject.Factory
interface AssistedFactory {
fun create (canteenId: String): MealPlanViewModel
}
companion object {
fun provideFactory(assistedFactory: AssistedFactory, canteenId: String): ViewModelProvider.Factory = object : ViewModelProvider.Factory {
override fun <T : ViewModel?> create(modelClass: Class<T>): T {
return assistedFactory.create(canteenId) as T
}
}
}
}
父片段：
class MealPlanFragment : Fragment() {
val canteenId = "mensa"
@Inject
lateinit var viewModelAssistedFactory: MealPlanViewModel.AssistedFactory
private val viewModel: MealPlanViewModel by viewModels {
MealPlanViewModel.provideFactory(viewModelAssistedFactory, canteenId)
}
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
val binding = FragmentMealPlanBinding.inflate(inflater, container, false)
val tabLayout = binding.tabLayout
val viewPager = binding.viewPager
viewPager.adapter = MealPlanPagerAdapter(childFragmentManager, lifecycle)
return binding.root
}
}
以及通过 viewpager 附加到父片段的子片段
@AndroidEntryPoint
class DayFragment : Fragment() {
private val viewModel: MealPlanViewModel by viewModels(
ownerProducer = {requireParentFragment()}
)
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
val binding = FragmentDayBinding.inflate(inflater, container, false)
viewModel.getMealPlanByDay(...).observe(viewLifecycleOwner, Observer {
...
})
return binding.root
}
companion object {
@JvmStatic
fun newInstance(position: Int) =
DayFragment().apply {
arguments = Bundle().apply {
putInt(POSITION, position)
}
}
}
}
的呼唤
viewModel.getMealPlanByDay(...).observe(viewLifecycleOwner, Observer {
})
导致以下错误：Cannot create an instance of class MealPlanViewModel has no zero argument constructor
但是，如果我不使用 AssistedInject 在父片段中创建 ViewModel 并像下面这样实例化它，我不会在子片段中得到“没有零参数构造函数”。
val bundle: Bundle = ...
val mealPlanRepository = ...
val mealPlanViewModelFactory = MealPlanViewModelFactory(mealPlanRepository, canteenId, this, bundle)
val viewModel = ViewModelProvider(this, mealPlanViewModelFactory).get(MealPlanViewModel::class.java)
关于为什么会这样以及如何在仍然使用 AssistedInject 的同时解决这个问题的任何想法？