无法创建ViewModel类的实例(无法启动活动ComponentInfo) [英] Cannot create an instance of ViewModel class (Unable to start activity ComponentInfo)

问题描述

• 无法创建自定义ViewModel的实例
• 无法创建ViewModel类的实例

• Cannot create an instance of custom ViewModel
• Cannot create an instance of class ViewModel

java.lang.RuntimeException:       
Unable to start activity ComponentInfo{ir.orangehat.movieinfo/ir.orangehat.movieinfo.application.home.HomeActivity}: java.lang.RuntimeException:

Cannot create an instance of class ir.orangehat.movieinfo.application.home.HomeViewModel

这是我的ViewModel，我认为问题出在我的构造函数中

public class HomeViewModel extends AndroidViewModel {

private MovieRepository movieRepository;

public HomeViewModel(@NonNull Application application, Context context, LifecycleOwner lifecycleOwner) {
    super(application);
    movieRepository = new MovieRepository(lifecycleOwner, context);
}

LiveData<List<Movie>> getMovies() {
    return movieRepository.getMovies();
}}

存储库

public class MovieRepository extends BaseRepository {

private LifecycleOwner lifecycleOwner;
private MovieApi movieApi;
private MovieDatabaseHelper movieDatabaseHelper;

public MovieRepository(LifecycleOwner lifecycleOwner, Context context) {
    this.lifecycleOwner = lifecycleOwner;
    movieApi = getRetrofitHelper().getService(MovieApi.class);
    movieDatabaseHelper = new MovieDatabaseHelper(context);
}

public LiveData<List<Movie>> getMovies() {
    LiveData<List<Movie>> moviesLiveData = movieApi.getMovieList();
    moviesLiveData.observe(lifecycleOwner, new Observer<List<Movie>>() {
        @Override
        public void onChanged(@Nullable List<Movie> movieArrayList) {
            movieDatabaseHelper.Save(movieArrayList);
        }
    });

    return movieDatabaseHelper.getAll();
} }

活动课程

public class HomeActivity extends AppCompatActivity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    // the error is here
    HomeViewModel homeViewModel = ViewModelProviders.of(this).get(HomeViewModel.class);

    homeViewModel.getMovies().observe(HomeActivity.this, new Observer<List<Movie>>() {
        @Override
        public void onChanged(@Nullable List<Movie> movieArrayList) {
            String str = null;
            if (movieArrayList != null) {
                str = Arrays.toString(movieArrayList.toArray());
            }
            Log.e("movies", str);
        }
    });
}

}

推荐答案

引用 AndroidViewModel 的文档:

Quoting the documentation for AndroidViewModel:

子类必须具有一个接受Application作为唯一参数的构造函数.

Subclasses must have a constructor which accepts Application as the only parameter.

您的构造函数不满足该要求.

Your constructor does not meet that requirement.

要么:

• 从HomeViewModel或

创建 a ViewModelProvider.Factory 可以构建您的HomeViewModel实例，并将该工厂与ViewModelProviders.of()

Create a ViewModelProvider.Factory that can build your HomeViewModel instances, and use that factory with ViewModelProviders.of()

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