android – MVVM Dagger2与组件中存在匹配键的绑定

我正在使用以下谷歌示例项目： https://github.com/googlesamples/android-architecture-components作为我的新项目的参考,并且难以尝试向项目添加第二个活动.

这是编译时遇到的错误

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

ActivityModule

@Module
public abstract class ActivityModule {

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

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

AppComponent

@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);
        }
    }
}

的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();
}

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);
}

应用

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;
    }
}

NavigationController

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);
    }
}

ContactActivity

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;
    }
}

解决方法

“组件中存在与匹配键的绑定”意味着您已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中访问它.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.使用@ContributesAndroidInjector生成子组件并在ActivityA模块中绑定Foo,但不绑定ActivityB模块.如果您使用@Inject Foo foo请求ActivityB中的Foo注入,您将收到该错误消息.

在您的特定情况下,您获得的错误可以通过以下方式重现：

>从GitHub克隆项目

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

>将MainActivity复制粘贴到新文件ContactsActivity中
>将MainActivityModule修改为与ActivityModule类似

因此,我们可以得出结论,您的ActivityModule存在问题. @ContributesAndroidInjector并不像看起来那么简单.它实际上意味着您要为在此处指定的活动创建新的Dagger 2子组件(请参阅docs here).

子组件可以使用父组件的绑定,但不能使用兄弟组件. ActivityModule中的两行ContributesAndroidInjector创建了两个兄弟子组件：一个用于MainActivity,另一个用于ContactsActivity.

但是,NavigationController依赖于MainActivity,MainActivity绑定在MainActivity子组件的对象图中,但不包含在ContactsActivity子组件的对象图中. AddContactsFragment已成为ContactsActivity子组件的对象图的一部分,并且不再具有对MainActivity的访问权限.这意味着当Dagger 2尝试在您的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“无法提供”部分.

虽然它无法在该特定对象图中提供MainActivity,但AndroidInjector一般都知道MainActivity,因此错误消息“存在绑定密钥”.这有什么约束力？将MainActivity.class绑定到MainActivityFactory的键.这个键的位置在哪里？在为ActiveActivity编写@ContributesAndroidInjector时的ActivityModule中.

如何解决这个问题超出了StackOverflow问题的范围,因为它涉及代码的冗长重构.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,因为它是你的两个活动的超类.然后,您需要停止使用ContributesAndroidInjector并为包含AppCompatActivity绑定的两个活动编写显式模块.

但是,现在请回到基础,并从更容易开始.这是一个灾难的秘诀,从一个复杂的项目开始,没有完全理解,只是修改它希望它可以工作.

Codepath Dagger 2 tutorial project更容易理解,让您熟悉Dagger 2中涉及的基本概念.一旦您熟悉了基本概念并理解了相关组件和子组件,那么您可以尝试更难的示例.祝好运！