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 viewModel，我需要 application 和 userData 来初始化这个 ScoreViewModel

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



}

但现在我很困惑如何在创建 viewModel 工厂时传递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)
    }

你的 viewModel 看起来像这样：

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

更多详情可以查看：https://github.com/Ali-Rezaei/News-Cache/blob/master/app/src/main/java/com/sample/android/news/viewmodels/NewsViewModel.kt