如何为AndroidViewModel创建视图模型工厂

Question

我需要在创建视图模型时传递值(userData(，所以我需要创建一个视图模型工厂

这是我的视图模型，我需要application和userData来初始化这个ScoreViewModel

class ScoreViewModel(application: Application, userData: UserKM) : AndroidViewModel(application) {

}

但现在我很困惑在创建viewModel工厂时如何通过application

class ScoreViewModelFactory(private val userData: UserKM) : ViewModelProvider.Factory {
override fun <T : ViewModel?> create(modelClass: Class<T>): T {
if (modelClass.isAssignableFrom(ScoreViewModel::class.java)) {
return ScoreViewModel(userData = userData,application = ?????? ) as T
}
throw IllegalArgumentException("Unknown ViewModel class")
}
}

我该怎么办？

Answer 1

你可以有这样的东西：

class Factory(val app: Application) : ViewModelProvider.Factory {
override fun <T : ViewModel?> create(modelClass: Class<T>): T {
if (modelClass.isAssignableFrom(NewsViewModel::class.java)) {
@Suppress("UNCHECKED_CAST")
return NewsViewModel(app) as T
}
throw IllegalArgumentException("Unable to construct viewmodel")
}
}

在你的活动或片段中，你有：

/**
* One way to delay creation of the viewModel until an appropriate lifecycle method is to use
* lazy. This requires that viewModel not be referenced before onActivityCreated, which we
* do in this Fragment.
*/
private val viewModel: NewsViewModel by lazy {
val activity = requireNotNull(this.activity) {
"You can only access the viewModel after onActivityCreated()"
}
ViewModelProviders.of(this, NewsViewModel.Factory(activity.application))
.get(NewsViewModel::class.java)
}

在这里，你的视图模型可以看起来像：

class NewsViewModel(application: Application) : AndroidViewModel(application)

有关更多详细信息，您可以查看：https://github.com/Ali-Rezaei/News-Cache/blob/master/app/src/main/java/com/sample/android/news/viewmodels/NewsViewModel.kt