java - ViewModel 没有零参数构造函数错误，原因是 ViewModelFactory 一直为 null(不是 100% 确定)

Question

到目前为止，我遵循 Android 开发人员指南了解架构组件，当然，问题是他们的示例无法与默认工厂一起使用，原因是“无零参数异常”。我遵循了 Google 示例存储库上的一些逻辑，以及相当多的 StackOverflow 建议答案、博客和教程。但我仍然遇到同样的错误。

现在，我想我已经找到了一个问题，似乎我的 ViewModelFactory 一直为 null，因此 ViewModelProvider 将其替换为默认 Factory，当然默认 Factory 需要一个零参数构造函数。但我仍然不知道代码到底出了什么问题。

所以我基本上有一个 ViewModelFactory

public class ViewModelFactory implements ViewModelProvider.Factory {

    private final Map<Class<? extends CustomViewModel>, Provider<CustomViewModel>> viewModels;

    @Inject
    public ViewModelFactory(Map<Class<? extends CustomViewModel>, Provider<CustomViewModel>> viewModels) {
        this.viewModels = viewModels;
    }

    @SuppressWarnings("unchecked")
    @Override
    public <T extends ViewModel> T create(Class<T> modelClass) {

        Provider<? extends CustomViewModel> viewModelProvider = viewModels.get(modelClass);

        if (viewModelProvider == null) {

            for (Map.Entry<Class<? extends CustomViewModel>, Provider<CustomViewModel>> entry : viewModels.entrySet()) {

                if (modelClass.isAssignableFrom(entry.getKey())) {

                    viewModelProvider = entry.getValue();
                    break;
                }
            }
        }

        if (viewModelProvider == null) {

            throw new IllegalArgumentException("unknown model class " + modelClass);
        }

        try {

            return (T) viewModelProvider.get();
        } catch (Exception e) {

            throw new RuntimeException(e);
        }
    }
}

和AppComponent

@Singleton
@Component(modules = {AndroidSupportInjectionModule.class, ViewModelModule.class})
public interface AppComponent {

    @Component.Builder
    interface Builder {

        @BindsInstance
        Builder application(App application);
        AppComponent build();
    }
    void inject(App application);
}

然后是ViewModelModule

@Module
public abstract class ViewModelModule {

    @Binds
    abstract ViewModelProvider.Factory bindViewModelFactory(ViewModelFactory viewModelFactory);

    @Binds
    @IntoMap
    @ViewModelKey(HourlyViewModel.class)
    abstract ViewModel bindHourlyViewModel(HourlyViewModel hourlyViewModel);
}

还有一个 ViewModelKey

@Documented
@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
@MapKey
@interface ViewModelKey {

    Class<? extends CustomViewModel> value();
}

还有一个 ViewModel

public class HourlyViewModel extends CustomViewModel {

    private LiveData<HourlyData> hourlyData;
    private MainRepository mainRepo;

    @Inject
    public HourlyViewModel(HourlyRepository mainRepo) {

        this.mainRepo = mainRepo;
    }

    @Override
    public void init(int id, long start, long stop) {
        super.init(id, start, stop);

        // some logic
    }
}

还有一个额外的 CustomViewModel

public class CustomViewModel extends ViewModel {

    public OpenDataApi api;

    public int id;
    public long start;
    public long stop;

    /**
     *
     * @param id
     * @param start
     * @param stop
     */
    public void init(int id, long start, long stop) {

        api = OpenDataApi.getRetrofitInstance().create(OpenDataApi.class);
        this.id = id;
        this.start = start;
        this.stop = stop;
    }
}

我的申请

public class App extends Application {

    @Override
    public void onCreate() {
        super.onCreate();

        DaggerAppComponent
                .builder()
                .application(this)
                .build()
                .inject(this);

        AndroidThreeTen.init(this);
    }
}

以及我如何尝试在 Fragment 中调用 ViewModel

public class FragmentHourly extends Fragment {

    @Inject
    ViewModelFactory viewModelFactory;

    private HourlyViewModel viewModel;

    @Override
    public void onActivityCreated(@Nullable Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);

        viewModel = ViewModelProviders.of(this, viewModelFactory).get(HourlyViewModel.class);
    }
}

我到底错过了什么？我的实现是否错误，或者缺少什么？

干杯并感谢您的帮助

Answer 1

我今天也遇到了类似的拦截器，错误是 fragment 中遗漏了以下代码:

`

@Override
public void onAttach(Context context) {
      AndroidSupportInjection.inject(this);
      super.onAttach(context);
}

`