已注册具有给定键的 SavedStateProvider

Question

我目前正在尝试使用savedState 的新Jetpack ViewModel。

    implementation 'androidx.lifecycle:lifecycle-viewmodel-savedstate:1.0.0-rc01'

我正在使用 1 个活动并尝试与 2 个片段共享 1 个 ViewModel，但是当我尝试启动第二个片段时，我从标题中收到错误消息。

这就是我使用savedInstance调用ViewModel的方式：

    val repository = (activity?.application as App).getRepository()
    viewModel = activity?.run {
        ViewModelFactory(repository, this, savedInstanceState).create(MainViewModel::class.java)
    } ?: throw Exception("Invalid Activity")

这是我的日志：

java.lang.IllegalArgumentException: SavedStateProvider with the given key is already registered
    at androidx.savedstate.SavedStateRegistry.registerSavedStateProvider(SavedStateRegistry.java:111)
    at androidx.lifecycle.SavedStateHandleController.attachToLifecycle(SavedStateHandleController.java:50)
    at androidx.lifecycle.SavedStateHandleController.create(SavedStateHandleController.java:70)
    at androidx.lifecycle.AbstractSavedStateViewModelFactory.create(AbstractSavedStateViewModelFactory.java:67)
    at androidx.lifecycle.AbstractSavedStateViewModelFactory.create(AbstractSavedStateViewModelFactory.java:84)
    at com.xxx.yyy.presentation.details.DetailsFragment.onCreate(DetailsFragment.kt:29)
    at androidx.fragment.app.Fragment.performCreate(Fragment.java:2586)
    at androidx.fragment.app.FragmentManagerImpl.moveToState(FragmentManagerImpl.java:838)
    at androidx.fragment.app.FragmentTransition.addToFirstInLastOut(FragmentTransition.java:1197)
    at androidx.fragment.app.FragmentTransition.calculateFragments(FragmentTransition.java:1080)
    at androidx.fragment.app.FragmentTransition.startTransitions(FragmentTransition.java:119)
    at androidx.fragment.app.FragmentManagerImpl.executeOpsTogether(FragmentManagerImpl.java:1866)
    at androidx.fragment.app.FragmentManagerImpl.removeRedundantOperationsAndExecute(FragmentManagerImpl.java:1824)
    at androidx.fragment.app.FragmentManagerImpl.execPendingActions(FragmentManagerImpl.java:1727)
    at androidx.fragment.app.FragmentManagerImpl$2.run(FragmentManagerImpl.java:150)

看起来它正在尝试使用已经注册的 SavedState 并因此出现错误？我认为这就是图书馆的全部意义所在。任何人都可以帮助或指出如何使用此传递参数到 ViewModel 并使用 savedStateHandle？

Answer 1

你永远不应该打电话给create自己——这样做，你实际上并没有使用ViewModel已经创建的保留，导致AbstractSavedStateViewModelFactory尝试多次注册相同的密钥。

相反，您应该将您ViewModelFactory的ViewModelProvider实例传递给一个实例以检索已经存在的 ViewModel 或仅在必要时创建它：

val repository = (activity?.application as App).getRepository()
viewModel = activity?.run {
    val factory = ViewModelFactory(repository, this, savedInstanceState)
    ViewModelProvider(this, factory).get(MainViewModel::class.java)
} ?: throw Exception("Invalid Activity")

如果您依赖于fragment-ktx版本1.1.0或更高版本，则可以改用by activityViewModelsKotlin 属性委托，它在幕后懒惰地使用ViewModelProvider：

val viewModel: MainViewModel by activityViewModels {
    val repository = (activity?.application as App).getRepository()
    ViewModelFactory(repository, requireActivity(), savedInstanceState)
}