android - ViewModelFactory can't create an instance 错误创建自定义ViewModelFactory类

Question

我正在尝试在 MVVM 架构中使用 Dagger2、Rxjava2、Retrofit2 设计一个应用程序。我在模型(存储库)类中得到响应，我想将其传递给我的 ViewModel，为此我必须设计自己的 ViewModelFactory 类。但我收到无法创建实例错误。这是我的类(class):型号:

private final NetworkService networkService;

public Model(NetworkService networkService) {
    this.networkService = networkService;
}

public LiveData<CakeResponse> getCakeList(){

    final MutableLiveData<CakeResponse> data = new MutableLiveData<>();

    networkService.getTheCakes().enqueue(new Callback<CakeResponse>() {
        @Override
        public void onResponse(Call<CakeResponse> call, Response<CakeResponse> response) {
            data.setValue(response.body());
        }

        @Override
        public void onFailure(Call<CakeResponse> call, Throwable t) {

        }
    });

    return data;

蛋糕 View 模型工厂:

public class CakeViewModelFactory implements ViewModelProvider.Factory{

private final Model model;
private final Application application;

@Inject
public CakeViewModelFactory(Model model, Application application) {

    this.model = model;
    this.application = application;
}


@NonNull
@Override
public <T extends ViewModel> T create(@NonNull Class<T> modelClass) {
    if (modelClass.isAssignableFrom(Model.class)) {
        return (T) new CakeViewModel(model, application);
    }
    throw new IllegalArgumentException("Unknown ViewModel class");
}

蛋糕 View 模型:

public class CakeViewModel extends AndroidViewModel {

private final LiveData<CakeResponse> cakeListObservable;

public CakeViewModel(@NonNull Model model, @NonNull Application application) {
    super(application);

    cakeListObservable = model.getCakeList();
}

public LiveData<CakeResponse> getCakeListObservable() {
    return cakeListObservable;
}

蛋糕 Activity

 @Inject
CakeViewModelFactory factory;

@BindView(R.id.recyclerView)
RecyclerView recyclerView;

List<CakeResponseCakes> cakes;
CakesAdapter adapter;

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

    CakeViewModel viewModel = ViewModelProviders.of(this, factory).get(CakeViewModel.class);

    DaggerCakeComponent.builder()
            .cakeModule(new CakeModule(this))
            .applicationComponent(CakeApplication.get(this).getComponent())
            .build().inject(this);

    ButterKnife.bind(this);

    initializeList();

    observeViewModel(viewModel);
}

private void observeViewModel(CakeViewModel cakeViewModel){
    cakeViewModel.getCakeListObservable().observeForever(new Observer<CakeResponse>() {
        @Override
        public void onChanged(@Nullable CakeResponse cakeResponse) {
            cakes = new ArrayList<>();
            if(cakeResponse != null) {
                CakeResponseCakes[] cakeList = cakeResponse.getCakes();
                if(cakeList != null) {
                    for(CakeResponseCakes caky: cakeList){
                        CakeResponseCakes cake = new CakeResponseCakes();
                        cake.setId(caky.getId());
                        cake.setDetailDescription(caky.getDetailDescription());
                        cake.setPreviewDescription(caky.getPreviewDescription());
                        cake.setTitle(caky.getTitle());
                        cake.setImage(caky.getImage());
                        cakes.add(cake);
                    }

                }
            }
            adapter.addCakes(cakes);
            adapter.notifyDataSetChanged();
        }
    });
}

@Override
protected void onDestroy() {
    super.onDestroy();
}

private void initializeList() {
    recyclerView.hasFixedSize();
    recyclerView.setLayoutManager(new LinearLayoutManager(this, LinearLayoutManager.VERTICAL, false));
    adapter = new CakesAdapter(getLayoutInflater());
    recyclerView.setAdapter(adapter);
}

这是我的 logCat:

 java.lang.RuntimeException: Unable to start activity ComponentInfo{ir.athenaishere.cakemvvm/ir.athenaishere.cakemvvm.activities.base.CakesActivity}: java.lang.RuntimeException: Cannot create an instance of class ir.athenaishere.cakemvvm.activities.base.mvvm.CakeViewModel
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2656)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2721)
        at android.app.ActivityThread.access$900(ActivityThread.java:168)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1393)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:135)
        at android.app.ActivityThread.main(ActivityThread.java:5753)
        at java.lang.reflect.Method.invoke(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:372)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1405)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1200)
     Caused by: java.lang.RuntimeException: Cannot create an instance of class ir.athenaishere.cakemvvm.activities.base.mvvm.CakeViewModel
        at android.arch.lifecycle.ViewModelProvider$AndroidViewModelFactory.create(ViewModelProvider.java:201)
        at android.arch.lifecycle.ViewModelProvider.get(ViewModelProvider.java:134)
        at android.arch.lifecycle.ViewModelProvider.get(ViewModelProvider.java:102)
        at ir.athenaishere.cakemvvm.activities.base.CakesActivity.onCreate(CakesActivity.java:51)
        at android.app.Activity.performCreate(Activity.java:6112)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1117)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2609)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2721) 
        at android.app.ActivityThread.access$900(ActivityThread.java:168) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1393) 
        at android.os.Handler.dispatchMessage(Handler.java:102) 
        at android.os.Looper.loop(Looper.java:135) 
        at android.app.ActivityThread.main(ActivityThread.java:5753) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at java.lang.reflect.Method.invoke(Method.java:372) 
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1405) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1200) 
     Caused by: java.lang.NoSuchMethodException: <init> [class android.app.Application]
        at java.lang.Class.getConstructor(Class.java:531)
        at java.lang.Class.getConstructor(Class.java:495)
        at android.arch.lifecycle.ViewModelProvider$AndroidViewModelFactory.create(ViewModelProvider.java:199)
        at android.arch.lifecycle.ViewModelProvider.get(ViewModelProvider.java:134) 
        at android.arch.lifecycle.ViewModelProvider.get(ViewModelProvider.java:102) 
        at ir.athenaishere.cakemvvm.activities.base.CakesActivity.onCreate(CakesActivity.java:51) 
        at android.app.Activity.performCreate(Activity.java:6112) 
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1117) 
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2609) 
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2721) 
        at android.app.ActivityThread.access$900(ActivityThread.java:168) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1393) 
        at android.os.Handler.dispatchMessage(Handler.java:102) 
        at android.os.Looper.loop(Looper.java:135) 
        at android.app.ActivityThread.main(ActivityThread.java:5753) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at java.lang.reflect.Method.invoke(Method.java:372) 
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1405) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1200)

更新:这是我的模块类:

@Module
public class CakeModule {
private CakesActivity cakesActivity;

public CakeModule(CakesActivity cakesActivity) {
    this.cakesActivity = cakesActivity;
}

@CakeContext
@BaseScope
@Provides
public CakesActivity providesCakeActivity() {
    return this.cakesActivity;
}

@BaseScope
@Provides
public Model providesModel(NetworkService networkService) {
    return new Model(networkService);
}

@BaseScope
@Provides
CakeViewModelFactory provideViewModel(Model model) {
    return new CakeViewModelFactory(model, cakesActivity.getApplication());
}

}

networkService 是我的 API 所在的接口(interface)。我的模型和应用程序在这个模块类中提供。

如有任何帮助，我们将不胜感激。 3>

Answer 1

我不确定，但是，在您的“CakeViewModelFactory”中，您正在执行构造函数注入(inject)，其中您正在注入(inject)模型和应用程序的实例，但是您的模块类没有提供应用程序上下文的@Provides 方法。所以可能将此添加到您的 Module 类中会有所帮助:

@Provides
public Context provideApplicationContext(Application application) {
     return applicaton;
}

并且还尝试在调用 CakesActivity 类中的 super.onCreate() 之前注入(inject)依赖项。

如果有任何解决方案解决了您的问题，请告诉我。 :)