MVVM Dagger2 组件中存在具有匹配键的绑定

Question

我正在使用以下 google 示例项目：https://github.com/googlesamples/android-architecture-components 作为我的新项目的参考，但在尝试向该项目添加第二个 activity 时遇到困难。

这是我在编译时得到的错误

Error:(22, 8) error: [dagger.android.AndroidInjector.inject(T)] com.apps.myapp.ui.common.MainActivity cannot be provided without an @Inject constructor or from an @Provides-annotated method. This type supports members injection but cannot be implicitly provided.
com.apps.myapp.ui.common.MainActivity is injected at
com.apps.myapp.ui.common.NavigationController.<init>(mainActivity)
com.apps.myapp.ui.common.NavigationController is injected at
com.apps.myapp.ui.addContacts.AddContactsFragment.navigationController
com.apps.myapp.ui.addContacts.AddContactsFragment is injected at
dagger.android.AndroidInjector.inject(arg0)
A binding with matching key exists in component: com.apps.myapp.di.ActivityModule_ContributeMainActivity.MainActivitySubcomponent

这是我的代码

活动模块

@Module
public abstract class ActivityModule {

    @ContributesAndroidInjector(modules = FragmentBuildersModule.class)
    abstract MainActivity contributeMainActivity();

    @ContributesAndroidInjector(modules = FragmentBuildersModule.class)
    abstract ContactActivity contributeContactActivity();
}

应用组件

@Singleton
@Component(modules = {
        AndroidInjectionModule.class,
        AppModule.class,
        ActivityModule.class})
public interface AppComponent {
    @Component.Builder
    interface Builder {
        @BindsInstance Builder application(Application application);
        AppComponent build();
    }
    void inject(App app);
}

AppInjector

public class AppInjector {
    private AppInjector() {}
    public static void init(App app) {DaggerAppComponent.builder().application(app).build().inject(app);
                    app.registerActivityLifecycleCallbacks(new Application.ActivityLifecycleCallbacks() {
                    @Override
                    public void onActivityCreated(Activity activity, Bundle savedInstanceState) {
                        handleActivity(activity);
                    }

                    @Override
                    public void onActivityStarted(Activity activity) {

                    }

                    @Override
                    public void onActivityResumed(Activity activity) {

                    }

                    @Override
                    public void onActivityPaused(Activity activity) {

                    }

                    @Override
                    public void onActivityStopped(Activity activity) {

                    }

                    @Override
                    public void onActivitySaveInstanceState(Activity activity, Bundle outState) {

                    }

                    @Override
                    public void onActivityDestroyed(Activity activity) {

                    }
                });
    }

    private static void handleActivity(Activity activity) {
        if (activity instanceof HasSupportFragmentInjector) {
            AndroidInjection.inject(activity);
        }
        if (activity instanceof FragmentActivity) {
            ((FragmentActivity) activity).getSupportFragmentManager()
                    .registerFragmentLifecycleCallbacks(
                            new FragmentManager.FragmentLifecycleCallbacks() {
                                @Override
                                public void onFragmentCreated(FragmentManager fm, Fragment f,
                                        Bundle savedInstanceState) {
                                    if (f instanceof Injectable) {
                                        AndroidSupportInjection.inject(f);
                                    }
                                }
                            }, true);
        }
    }
}

AppModule

@Module(includes = ViewModelModule.class)
class AppModule {
    @Singleton @Provides
    BnderAPIService provideService() {
        return new Retrofit.Builder()
                .baseUrl("serverurl")
                .addConverterFactory(GsonConverterFactory.create())
                .addCallAdapterFactory(new LiveDataCallAdapterFactory())
                .build()
                .create(APIService.class);
    }

    @Singleton @Provides
    Db provideDb(Application app) {
        return Room.databaseBuilder(app, Db.class,"Db.db").build();
    }

    @Singleton @Provides
    UserDao provideUserDao(Db db) {
        return db.userDao();
    }

    @Singleton @Provides
    ContactDao provideContactDao(Db db) {
        return db.contactDao();
    }
}

FragmentBuildersModule

@Module
public abstract class FragmentBuildersModule {

    @ContributesAndroidInjector
    abstract AddContactsFragment contributeAddUserFragment();

    @ContributesAndroidInjector
    abstract ContactsFragment contributeContactsFragment();

    @ContributesAndroidInjector
    abstract ChalkboardFragment contributeChalkboardFragment();
}

可注射

public interface Injectable {
}

ViewModelKey

@Documented
@Target({ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@MapKey
@interface ViewModelKey {
    Class<? extends ViewModel> value();
}

ViewModelModule

@Module
abstract class ViewModelModule {
    @Binds
    @IntoMap
    @ViewModelKey(AddContactsViewModel.class)
    abstract ViewModel bindAddContactsViewModel(AddContactsViewModel addContactsViewModel);

    @Binds
    @IntoMap
    @ViewModelKey(ContactsViewModel.class)
    abstract ViewModel bindContactsViewModel(ContactsViewModel contactsViewModel);

    @Binds
    @IntoMap
    @ViewModelKey(ChalkboardViewModel.class)
    abstract ViewModel bindChalkboardViewModel(ChalkboardViewModel chalkboardViewModel);

    @Binds
    abstract ViewModelProvider.Factory bindViewModelFactory(ViewModelFactory factory);
}

申请

public class App extends Application implements HasActivityInjector {

    @Inject
    DispatchingAndroidInjector<Activity> dispatchingAndroidInjector;
    @Override
    protected void attachBaseContext(Context base) {
        super.attachBaseContext(base);
        MultiDex.install(this);
    }
    @Override
    public void onCreate() {
        super.onCreate();
        if (BuildConfig.DEBUG) {

        }
        AppInjector.init(this);
    }

    @Override
    public DispatchingAndroidInjector<Activity> activityInjector() {
        return dispatchingAndroidInjector;
    }
}

导航控制器

public class NavigationController {
    private final int containerId;
    private final FragmentManager fragmentManager;
    @Inject
    public NavigationController(MainActivity mainActivity) {
        this.containerId = R.id.container;
        this.fragmentManager = mainActivity.getSupportFragmentManager();
    }

    public void navigateToUsers() {
        Log.i("TAG", "Navigate to users");
        String tag = "users";
        AddContactsFragment userFragment = AddContactsFragment.create();
        fragmentManager.beginTransaction()
                .replace(containerId, userFragment, tag)
                .addToBackStack(null)
                .commitAllowingStateLoss();
    }

    public void navigateToContacts() {
        Log.i("TAG", "Navigate to contacts");
        String tag = "contacts";
        ContactsFragment contactsFragment = ContactsFragment.create();
        fragmentManager.beginTransaction()
                .add(contactsFragment, tag)
                .addToBackStack(null)
                .commitAllowingStateLoss();
    }

    public void navigateToChalkboard() {
        Log.i("TAG", "Navigate to chalkboard");
        String tag = "chalkboard";
        ChalkboardFragment chalkboardFragment = ChalkboardFragment.create();
        fragmentManager.beginTransaction()
                .add(chalkboardFragment, tag)
                .addToBackStack(null)
                .commitAllowingStateLoss();
    }
}

主要活动

public class MainActivity extends AppCompatActivity implements LifecycleRegistryOwner, HasSupportFragmentInjector {
    private final LifecycleRegistry lifecycleRegistry = new LifecycleRegistry(this);
    @Inject
    DispatchingAndroidInjector<Fragment> dispatchingAndroidInjector;
    @Inject
    NavigationController navigationController;
    private Toolbar toolbar;
    @Override
    public LifecycleRegistry getLifecycle() {
        return lifecycleRegistry;
    }

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        ActivityMainBinding binding = DataBindingUtil.setContentView(this, R.layout.activity_main);
        binding.setHandler(this);
        binding.setManager(getSupportFragmentManager());
        toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
    }

    @Override
    public DispatchingAndroidInjector<Fragment> supportFragmentInjector() {
        return dispatchingAndroidInjector;
    }

    static class ViewPagerAdapter extends FragmentPagerAdapter {
        private final List<Fragment> mFragmentList = new ArrayList<>();
        private final List<String> mFragmentTitleList = new ArrayList<>();

        public ViewPagerAdapter(FragmentManager manager) {
            super(manager);
        }

        @Override
        public Fragment getItem(int position) {
            return mFragmentList.get(position);
        }

        @Override
        public int getCount() {
            return mFragmentList.size();
        }

        public void addFragment(Fragment fragment, String title) {
            mFragmentList.add(fragment);
            mFragmentTitleList.add(title);
        }

        @Override
        public CharSequence getPageTitle(int position) {
            return mFragmentTitleList.get(position);
        }
    }

    @BindingAdapter({"handler"})
    public static void bindViewPagerAdapter(final ViewPager view, final MainActivity activity) {
        final ViewPagerAdapter adapter = new ViewPagerAdapter(activity.getSupportFragmentManager());
        adapter.addFragment(new ChalkboardFragment(), "Chalkboard");
        adapter.addFragment(new ContactsFragment(), "Contacts");
        view.setAdapter(adapter);
    }

    @BindingAdapter({"pager"})
    public static void bindViewPagerTabs(final TabLayout view, final ViewPager pagerView) {
        view.setupWithViewPager(pagerView, true);
    }
}

联系活动

public class ContactActivity extends AppCompatActivity implements LifecycleRegistryOwner, HasSupportFragmentInjector {
    private final LifecycleRegistry lifecycleRegistry = new LifecycleRegistry(this);
    @Inject
    DispatchingAndroidInjector<Fragment> dispatchingAndroidInjector;
    @Override
    public LifecycleRegistry getLifecycle() {
        return lifecycleRegistry;
    }

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_contact);
        if (savedInstanceState == null) {

        }
    }

    @Override
    public DispatchingAndroidInjector<Fragment> supportFragmentInjector() {
        return dispatchingAndroidInjector;
    }
}

Answer 1

"A binding with matching key exists in component" 表示您在整个对象图中的某处绑定了一个依赖项，但无法从需要注入它的子组件到达它。这是 javadoc：

Utility code that looks for bindings matching a key in all subcomponents in a binding graph so that a user is advised that a binding exists elsewhere when it is not found in the current subgraph. If a binding matching a key exists in a sub- or sibling component, that is often what the user actually wants to use.

例如，假设您有两个活动，ActivityA 和 ActivityB。您使用 @ContributesAndroidInjector 生成子组件并在 ActivityA 模块中绑定 Foo 而不是 ActivityB 模块。如果您请求使用 @Inject Foo foo 在 ActivityB 中注入 Foo，您将收到该错误消息。

在您的特定情况下，您遇到的错误可以通过以下方式重现：

正在从 GitHub

克隆项目

git clone https://github.com/googlesamples/android-architecture-components.git`

复制粘贴 MainActivity 到一个新文件中 ContactsActivity
修改 MainActivityModule 使其看起来像您的 ActivityModule

所以由此我们可以断定你的ActivityModule是有问题的。 @ContributesAndroidInjector 并不像看起来那么简单。这实际上意味着您正在为您在此处指定的 Activity 创建一个新的 Dagger 2 子组件（请参阅 docs here）。

子组件可以使用父组件的绑定，但不能使用同级组件。 ActivityModule 中 ContributesAndroidInjector 的两行创建两个同级子组件：一个用于 MainActivity 和一个用于 ContactsActivity.

但是，NavigationController 依赖于 MainActivity，它在 MainActivity 子组件的对象图中绑定，但在 ContactsActivity 子组件的对象图中不绑定。 AddContactsFragment 已成为 ContactsActivity 子组件对象图的一部分，并且无法再访问 MainActivity。这意味着当 Dagger 2 试图在你的 AddContactsFragment 中注入 NavigationController 时，它无法提供 MainActivity 作为它的依赖项。这解释了错误消息的 "cannot provide" 部分。

虽然它不能在那个特定的对象图中提供 MainActivity，但是 AndroidInjector 大体上知道 MainActivity 因此错误消息 "a binding key exists"。这是什么绑定密钥？将 MainActivity.class 绑定到 MainActivityFactory 的键。这个键绑定在哪里？在 ActivityModule 中，当您为 MainActivity 编写 @ContributesAndroidInjector 时。

如何解决这个问题超出了 Whosebug 问题的范围，因为它涉及冗长的代码重构。您需要重新组织对象图，以便 NavigationController 不再依赖于 MainActivity。也许你可以让它依赖于 AppCompatActivity，因为它是你两个活动的超类。然后您将需要停止使用 ContributesAndroidInjector 并为您的两个 Activity 编写显式模块，其中包括 AppCompatActivity.

的绑定

但是，现在请回到基础并从更简单的事情开始。在没有完全理解的情况下开始一个复杂的项目，然后只是修改它，希望它能工作，这是灾难的根源。

Codepath Dagger 2 tutorial project更容易理解，会让你熟悉Dagger 2中涉及的基本概念。一旦你熟悉了基本概念并理解了依赖组件和子组件，那么你可以尝试一个更难的例子。祝你好运！

MVVM Dagger2 组件中存在具有匹配键的绑定

MVVM Dagger2 A Binding With Matching Key Exists in Component

android

mvvm

dagger-2

android-mvvm

android-architecture-components