Android Inject Dependency (Dagger 2) Inside Fragment 使用@ContributesAndroidInjector

Question

我正在使用 Dagger 2在我的项目中进行依赖注入(inject)

问题是当我试图在依赖于 FragmentManager 的 fragment 类中注入(inject) ViewPageAdapter 时，如下所示:

@Inject
lateinit var mainTripsFragmentAdapter: MainTripsFragmentAdapter

我收到以下构建错误:

error: [dagger.android.AndroidInjector.inject(T)] android.support.v4.app.FragmentManager cannot be provided without an @Provides-annotated method.
public abstract interface AppComponent extends dagger.android.AndroidInjector { ^ android.support.v4.app.FragmentManager is injected at com.example.presenters.main.trips.MainTripsFragmentAdapter.(fragmentManager, …) com.example.presenters.main.trips.MainTripsFragmentAdapter is injected at com.example.presenters.main.trips.MainTripsFragment.mainTripsFragmentAdapter com.example.presenters.main.trips.MainTripsFragment is injected at com.example.presenters.main.MainActivity.tripsFragment com.example.presenters.main.MainActivity is injected at dagger.android.AndroidInjector.inject(arg0) A binding with matching key exists in component: com.example.di.FragmentBuilder_BindMainTripsFragment$app_debug.MainTripsFragmentSubcomponent

我研究了3天，看了很多文章，都没有弄清楚问题出在哪里!
相关代码我贴出来，如果太长请见谅

需要PagerAdapter的Fragment:

class MainTripsFragment @Inject constructor() : BaseFragment() {

    @Inject
    lateinit var mainTripsFragmentAdapter: MainTripsFragmentAdapter

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        pager.adapter = mainTripsFragmentAdapter
    }
}

基础 fragment :

abstract class BaseFragment : DaggerFragment() {

    override fun onAttach(context: Context?) {
        AndroidSupportInjection.inject(this)
        super.onAttach(context)
    }

    override fun onCreateView(
            inflater: LayoutInflater,
            container: ViewGroup?,
            savedInstanceState: Bundle?
    ): View? = inflater.inflate(getLayout(), container, false)

    abstract fun getLayout(): Int
}

这是FragmentPagerAdapter:

class MainTripsFragmentAdapter @Inject constructor(
    fragmentManager: FragmentManager,
    private val mainCurrentTripsFragment: MainCurrentTripsFragment,
    private val mainHistoryTripsFragment: MainHistoryTripsFragment
) : FragmentPagerAdapter(fragmentManager) {

    override fun getItem(position: Int) = when (position) {
        0 -> mainCurrentTripsFragment
        1 -> mainHistoryTripsFragment
        else -> mainCurrentTripsFragment
    }

    override fun getCount() = 2
}

这里是 DI 相关类:

应用组件:

@Singleton
@Component(modules = [
    AndroidInjectionModule::class,
    ActivityBuilder::class,
    FragmentBuilder::class
])

interface AppComponent : AndroidInjector<DaggerApplication> {

    fun inject(app: App)

    override fun inject(instance: DaggerApplication)

    @Component.Builder
    interface Builder {
        @BindsInstance
        fun application(app: Application): Builder

        fun build(): AppComponent
    }
}

fragment 生成器:

@Module
abstract class FragmentBuilder {

    @ContributesAndroidInjector
    internal abstract fun bindMainHomeFragment(): MainHomeFragment

    @Module
    internal interface MainTripsFragmentModule {

        @Binds
        fun bindMainTripsFragment(fragment: MainTripsFragment): Fragment
    }

    @ContributesAndroidInjector(modules = [FragmentModule::class, MainTripsFragmentModule::class])
    internal abstract fun bindMainTripsFragment(): MainTripsFragment

    @ContributesAndroidInjector
    internal abstract fun bindMainCurrentTripsFragment(): MainCurrentTripsFragment
    @ContributesAndroidInjector
    internal abstract fun bindMainHistoryTripsFragment(): MainHistoryTripsFragment
}

fragment 模块:

@Module
class FragmentModule {

    @Provides
    fun provideFragmentManager(fragment: Fragment) = fragment.childFragmentManager
}

Activity 构建器:

@Module
abstract class ActivityBuilder {

    @ContributesAndroidInjector
    internal abstract fun contributeMainActivity(): MainActivity
}

主要 Activity :

class MainActivity : BaseActivity() {

     @Inject
     lateinit var tripsFragment: MainTripsFragment

     override fun onCreate(savedInstanceState: Bundle?) {
         super.onCreate(savedInstanceState)
         setContentView(R.layout.activity_main)

         showFragment(tripsFragment)
     }

     private fun showFragment(fragment: Fragment) {
         supportFragmentManager
                 .beginTransaction()
                 .replace(R.id.layout_container, fragment)
                 .commit()
     }
 }

基础 Activity :

@SuppressLint("Registered")
abstract class BaseActivity : AppCompatActivity(), HasSupportFragmentInjector {

@Inject
lateinit var fragmentInjector: DispatchingAndroidInjector<Fragment>

    override fun onCreate(savedInstanceState: Bundle?) {
        AndroidInjection.inject(this)
        super.onCreate(savedInstanceState)
    }
    override fun supportFragmentInjector() = fragmentInjector
}

应用类:

class App : Application(), HasActivityInjector {
    @Inject
    lateinit var activityInjector: DispatchingAndroidInjector<Activity>

    override fun activityInjector(): AndroidInjector<Activity> = activityInjector

    override fun onCreate() {
        super.onCreate()

        DaggerAppComponent.builder()
                .application(this)
                .build()
                .apply {
                    inject(this@App)
                }

    }
}

有一点是，如果我在我的 Activity 中 @Inject PagerAdapter(我也应该为它添加一个模块)它工作正常。
哪一部分实现错误？

Answer 1

这里有很多问题:

class MainTripsFragmentAdapter @Inject constructor(
    fragmentManager: FragmentManager,
    private val mainCurrentTripsFragment: MainCurrentTripsFragment,
    private val mainHistoryTripsFragment: MainHistoryTripsFragment
) : FragmentPagerAdapter(fragmentManager) {

    override fun getItem(position: Int) = when (position) { 
        0 -> mainCurrentTripsFragment  //no!!
        1 -> mainHistoryTripsFragment
        else -> mainCurrentTripsFragment
    }

    override fun getCount() = 2
}

PagerAdapter 中的

getItem 表示“创建项目”。当您使用 PagerAdapter 时，您会将 fragment 的创建委托(delegate)给适配器。您不应该编写代码来缓存和存储 fragment ，这是 FragmentManager 的工作。

您的 FragmentAdapter 应该看起来像这样:

    override fun getItem(position: Int) = when (position) { 
        0 -> MainCurrentTripsFragment.instantiate()
        1 -> MainHistoryTripsFragment.instantiate()
        else -> MainCurrentTripsFragment.instantiate()
    }

instantiate 方法在 fragment 中的伴生对象中声明:

class MainCurrentTripsFragment: Fragment() {
    companion object {
        @JvmStatic
        fun instantiate(args: Bundle?) {
            val frag = MainCurrentTripsFragment()
            frag.arguments = args
        }
    }
}

这是在 Android 中使用带有 Fragment 的 PagerAdapter 的标准习惯用法。您不应在对象图中提供 PagerAdapters 或 Fragments 作为依赖项。事实上，许多由操作系统控制的 Android 类，如 FragmentManager、Activity、Fragment、BroadcastReceiver、服务 不是使用 Dagger 2 成为对象图中依赖项的良好候选者。

开始使用 Dagger 2 时的一个常见错误是尝试注入(inject)一切，就好像手动更新任何东西都是错误的一样。这在 Android 中是不可能的。

请从您的模块中取出 Fragments、FragmentManager、PagerAdapter 等。不要尝试使用 Dagger 2 提供或绑定(bind)这些。然后使用 Dagger 2 注入(inject)域层或数据层对象，如存储库、Retrofit 服务等。如果你遇到困难，你可以随时发布另一个问题。

并查看官方 Google Android Architecture blueprints .理想情况下，您的解决方案应该类似于它们。