ViewModelProviders with Dagger 2,无法掌握概念 [英] ViewModelProviders with Dagger 2, not able to grasp the concept

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问题描述

我有这样的改造服务

public interface BrandsService {
    @GET("listBrand")
    Call<List<Brand>> getBrands();
}

然后我有一个存储库来从这样的 api 中获取数据

Then I have a Repository to get data from an api like this

public class BrandsRepository {
    public static final String TAG = "BrandsRepository";
    MutableLiveData<List<Brand>> mutableLiveData;
    Retrofit retrofit;

    @Inject
    public BrandsRepository(Retrofit retrofit) {
        this.retrofit = retrofit;
    }

    public LiveData<List<Brand>> getListOfBrands() {
//       Retrofit retrofit = ApiManager.getAdapter();
        final BrandsService brandsService = retrofit.create(BrandsService.class);
        Log.d(TAG, "getListOfBrands: 00000000000 "+retrofit);

        mutableLiveData = new MutableLiveData<>();

        Call<List<Brand>> retrofitCall = brandsService.getBrands();
        retrofitCall.enqueue(new Callback<List<Brand>>() {
            @Override
            public void onResponse(Call<List<Brand>> call, Response<List<Brand>> response) {
                mutableLiveData.setValue(response.body());
            }

            @Override
            public void onFailure(Call<List<Brand>> call, Throwable t) {
                t.printStackTrace();
            }
        });
        return mutableLiveData;

    }
}

我通过像这样注入 Retrofit 来使用 Dagger2 的构造函数注入.然后我有一个这样的 ViewModel

I am using constructor injection of Dagger2 by injecting Retrofit like that. Then I have a ViewModel like this

public class BrandsViewModel extends ViewModel{
    BrandsRepository brandsRepository;
    LiveData<List<Brand>> brandsLiveData;
    @Inject
    public BrandsViewModel(BrandsRepository brandsRepository) {
        this.brandsRepository = brandsRepository;
    }

    public void callService(){
       brandsLiveData = brandsRepository.getListOfBrands();
    }

    public LiveData<List<Brand>> getBrandsLiveData() {
        return brandsLiveData;
    }


}

要在 BrandsRepository 中注入 Retrofit,我必须像这样注入 BrandsRepository.然后我有这样的 MainActivity

To inject Retrofit in BrandsRepository, I have to inject BrandsRepository like that. Then I have MainActivity like this

public class MainActivity extends AppCompatActivity {
    private static final String TAG = "MainActivity";
    @Inject
    BrandsViewModel brandsViewModel;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        ((MainApplication)getApplication()).getNetComponent().inject(this);

//        BrandsViewModel brandsViewModel = ViewModelProviders.of(this).get(BrandsViewModel.class);
        brandsViewModel.callService();

        LiveData<List<Brand>> brandsLiveData = brandsViewModel.getBrandsLiveData();
        brandsLiveData.observe(this, new Observer<List<Brand>>() {
            @Override
            public void onChanged(@Nullable List<Brand> brands) {
                Log.d(TAG, "onCreate: "+brands.get(0).getName());
            }
        });


    }
}

BrandsViewModel 是使用 Dagger2 而不是 ViewModelProviders 注入的.这工作正常,但是当我尝试通过取消注释来使用 ViewModelProviders 时,dagger 给了我一个明显的错误.获取 ViewModel 的正确方法是使用 ViewModelProviders,但我将如何在注入这样的改造的同时实现这一点.

The BrandsViewModel is injected using Dagger2 rather than ViewModelProviders. This is working fine but when I try to use ViewModelProviders by uncommenting it, dagger gives me the error which is obvious. The proper way of getting a ViewModel is by using ViewModelProviders but how will I accomplish this while injecting retrofit like that.

推荐答案

重要说明.要使用 Jetpack ViewModel,您不需要地图多重绑定.继续阅读.

An important note. To use Jetpack ViewModel, you don't need map-multibinding. Read on.

答案可能比 Mumi 的方法更简单,即您在组件上公开 ViewModel:

The answer can be simpler than Mumi's approach, which is that you expose the ViewModel on your component:

@Singleton
@Component(modules={...})
public interface SingletonComponent {
    BrandsViewModel brandsViewModel();
}

现在您可以在 ViewModelFactory 内的组件上访问此方法:

And now you can access this method on the component inside the ViewModelFactory:

// @Inject
BrandsViewModel brandsViewModel;

...
brandsViewModel = new ViewModelProvider(this, new ViewModelProvider.Factory() {
    @Override
    public <T extends ViewModel> create(Class<T> modelClazz) {
        if(modelClazz == BrandsViewModel.class) {
            return singletonComponent.brandsViewModel();
        }
        throw new IllegalArgumentException("Unexpected class: [" + modelClazz + "]");
    }).get(BrandsViewModel.class);

<小时>

所有这些都可以用 Kotlin 简化和隐藏:


All this can be simplified and hidden with Kotlin:

inline fun <reified T: ViewModel> AppCompatActivity.createViewModel(crossinline factory: () -> T): T = T::class.java.let { clazz ->
    ViewModelProvider(this, object: ViewModelProvider.Factory {
        override fun <T : ViewModel?> create(modelClass: Class<T>): T {
            if(modelClass == clazz) {
                @Suppress("UNCHECKED_CAST")
                return factory() as T
            }
            throw IllegalArgumentException("Unexpected argument: $modelClass")
        }
    }).get(clazz)
}

现在让你做

brandsViewModel = createViewModel { singletonComponent.brandsViewModel() }

现在 BrandsViewModel 可以从 Dagger 接收参数的地方:

Where now BrandsViewModel can receive its parameters from Dagger:

class BrandsViewModel @Inject constructor(
    private val appContext: Context,
    /* other deps */
): ViewModel() {
    ...
}

虽然如果 Provider 从 Dagger 中暴露出来,那么意图可能会更清晰

Though the intent might be cleaner if a Provider<BrandsViewModel> is exposed from Dagger instead

interface SingletonComponent {
    fun brandsViewModel(): Provider<BrandsViewModel>
}

brandsViewModel = createViewModel { singletonComponent.brandsViewModel().get() }

<小时>

通过 android-ktx 的一些额外技巧,你甚至可以做到


With some additional trickery coming in from android-ktx, you could even do

@Suppress("UNCHECKED_CAST")
inline fun <reified T : ViewModel> Fragment.fragmentViewModels(
    crossinline creator: () -> T
): Lazy<T> {
    return createViewModelLazy(T::class, storeProducer = {
        viewModelStore
    }, factoryProducer = {
        object : ViewModelProvider.Factory {
            override fun <T : ViewModel?> create(
                modelClass: Class<T>
            ): T = creator.invoke() as T
        }
    })
}

然后

class ProfileFragment: Fragment(R.layout.profile_fragment) {
    private val viewModel by fragmentViewModels {
        singletonComponent.brandsViewModelFactory().get()
    }

brandsViewModelFactory() 在哪里

fun brandsViewModelFactory(): Provider<BrandsViewModel>

这篇关于ViewModelProviders with Dagger 2,无法掌握概念的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!

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