android - 无法创建 ViewModel 类的实例(无法启动 Activity ComponentInfo)

Question

我在我的项目中使用 MVVM、Retrofit、LiveData，但在我看到这些链接之前出现此错误

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

错误

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
                  

View 模型

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();
} }

Activity 类

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);
            }
        });
    }
}

我应该在我的项目和自定义工厂中使用 Dagger 吗？

Answer 1

引用 the documentation for AndroidViewModel :

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

您的构造函数不符合该要求。

或者:

• 从 HomeViewModel 中删除 Context 上下文 和 LifecycleOwner lifecycleOwner 构造函数参数，或者

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

一起使用