android - 在 android kotlin mvvm 中没有主构造函数就不可能进行超类型初始化

Question

我正在尝试做的事情：

我正在尝试将 viewModel 链接到活动并在两者之间使用工厂

在MainActivity.kt

KtMainActivityViewModelFactory    ktMainActivityViewModel = ViewModelProviders.of(this,ktMainActivityViewModelFactory).get(KtMainActivityViewModel::class.java)

KtMainActivityViewModelFactory.kt

class KtMainActivityViewModelFactory : ViewModelProvider.Factory {


    private val movieRepository: MovieRepository
    private val database: MoviesAppDatabase
    private val dataservice: MovieDataService

    @Inject
    constructor(movieRepository: MovieRepository, database: MoviesAppDatabase, dataservice: MovieDataService) {
        this.movieRepository = movieRepository
        this.database = database
        this.dataservice = dataservice
    }


    override fun <T : ViewModel> create(modelClass: Class<T>): T {
        return KtMainActivityViewModelFactory(movieRepository, database, dataservice) as T
    }


}

KtMainActivityViewModel.kt

class KtMainActivityViewModel : ViewModel() {


    private val movieRepository: MovieRepository
    private val database: MoviesAppDatabase
    private val dataservice: MovieDataService


    constructor(movieRepository: MovieRepository, database: MoviesAppDatabase, dataservice: MovieDataService) : super() {
        this.movieRepository = movieRepository
        this.database = database
        this.dataservice = dataservice
    }


}

错误：

标签： androidkotlinmvvm

Answer 1

由于您只有一个构造函数，因此应将其设为主要构造函数：

class KtMainActivityViewModel(private val movieRepository: MovieRepository, private val database: MoviesAppDatabase, private val dataservice: MovieDataService) : ViewModel() { ... }

作为额外的好处，这样您还需要提及每个属性一次而不是 4 次。

请注意，您可以在正文中声明private val movieRepository: MovieRepository等

class KtMainActivityViewModel(movieRepository: MovieRepository, database: MoviesAppDatabase, dataservice: MovieDataService) : ViewModel() { 
    private val _movieRepository: MovieRepository = movieRepository
    ...
}

但没有理由这样做。

当然这也适用于KtMainActivityViewModelFactory：

class KtMainActivityViewModelFactory @Inject constructor(private val movieRepository: MovieRepository, private val database: MoviesAppDatabase, private val dataservice: MovieDataService) : ViewModelProvider.Factory {

    override fun <T : ViewModel> create(modelClass: Class<T>): T {
        return KtMainActivityViewModelFactory(movieRepository, database, dataservice) as T
    }

}