在android kotlin mvvm中，如果没有主构造函数，超级类型初始化是不可能的

我想做什么：

我试图将viewModel链接到活动中，并在两者之间使用工厂

在MainActivity.kt中

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

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
    }


}

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
    }


}

KtMainActivityViewModelFactory.kt

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

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
    }


}

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：

您应该添加主构造函数并将

super（）

替换为

this（）

---

尝试将其更改为

KtMainActivityViewModel:ViewModel

，因为您只有一个构造函数，所以应该将其设置为主构造函数：

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

作为一个额外的好处，这种方式你还需要提到每个属性一次，而不是4次

注意，您可以在body中声明

private val movieRepository:movieRepository

等

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

但是没有理由这么做

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
    }

}

class KtMainActivityViewModelFactory@Inject构造函数（私有val movieRepository:movieRepository，私有val数据库：MOVIESAPPDABASE，私有val数据服务：MOVIEDASERVICE）：ViewModelProvider.Factory{
重写趣味创建（modelClass:Class）：T{
将KtMainActivityViewModelFactory（移动存储库、数据库、数据服务）返回为T
}
}

这不会编译，因为属性未初始化。@Alexey Romanov他只要求消除该错误，并纠正了该错误