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使用@Assisted带有 savedStateHandleby viewModels()的注释，并且可以将 SavedStateHandle 对象注入到 ViewModel 中的模块中，这些模块不是带有匕首柄的动态功能模块

@AndroidEntryPoint
class MainActivity : AppCompatActivity() {

    private val viewModel: MainActivityViewModel by viewModels()

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
    }
}

class MainActivityViewModel @ViewModelInject constructor(
    @Assisted savedStateHandle: SavedStateHandle
) : ViewModel() {

    val stringData = savedStateHandle.getLiveData<String>("hello_world")
}

但是动态功能模块不可能这样做。动态功能模块 ViewModels 是如何完成的？

4

1 回答 1

3

我的视图模型是

class DashboardViewModel @ViewModelInject constructor(
    @Assisted private val savedStateHandle: SavedStateHandle,
    private val coroutineScope: CoroutineScope,
    private val dashboardStatsUseCase: GetDashboardStatsUseCase,
    private val setPropertyStatsUseCase: SetPropertyStatsUseCase
) : ViewModel() {

}

FragmentFactory为 SavedStateHandle创建泛型

interface ViewModelFactory<out V : ViewModel> {
    fun create(handle: SavedStateHandle): V
}

class GenericSavedStateViewModelFactory<out V : ViewModel>(
    private val viewModelFactory: ViewModelFactory<V>,
    owner: SavedStateRegistryOwner,
    defaultArgs: Bundle? = null
) : AbstractSavedStateViewModelFactory(owner, defaultArgs) {
    @Suppress("UNCHECKED_CAST")
    override fun <T : ViewModel> create(
        key: String,
        modelClass: Class<T>,
        handle: SavedStateHandle
    ): T {
        return viewModelFactory.create(handle) as T
    }
}

/**
 * Convenience function to use with `by viewModels` that creates an instance of
 * [AbstractSavedStateViewModelFactory] that enables us to pass [SavedStateHandle]
 * to the [ViewModel]'s constructor.
 *
 * @param factory instance of [ViewModelFactory] that will be used to construct the [ViewModel]
 * @param owner instance of Fragment or Activity that owns the [ViewModel]
 * @param defaultArgs Bundle with default values to populate the [SavedStateHandle]
 *
 * @see ViewModelFactory
 */
@MainThread
inline fun <reified VM : ViewModel> SavedStateRegistryOwner.withFactory(
    factory: ViewModelFactory<VM>,
    defaultArgs: Bundle? = null
) = GenericSavedStateViewModelFactory(factory, this, defaultArgs)

ViewModel 的 ViewModel 工厂

class DashboardViewModelFactory @Inject constructor(
    private val coroutineScope: CoroutineScope,
    private val dashboardStatsUseCase: GetDashboardStatsUseCase,
    private val setPropertyStatsUseCase: SetPropertyStatsUseCase
) : ViewModelFactory<DashboardViewModel> {

    override fun create(handle: SavedStateHandle): DashboardViewModel {
        return DashboardViewModel(
            handle,
            coroutineScope,
            dashboardStatsUseCase,
            setPropertyStatsUseCase
        )
    }
}

并使用 Fragment 中的 DashBoardViewModelFactory 创建 ViewModel 作为

@Inject
lateinit var dashboardViewModelFactory: DashboardViewModelFactory

private val viewModel: DashboardViewModel
by viewModels { withFactory(dashboardViewModelFactory) }

在这里，您可以看到完整的实施。我无法找到我用来实现此解决方案的来源，如果您可以评论链接，我想感谢作者。

于 2020-10-19T18:57:31.190 回答