为什么 dagger 不能处理这些 kotlin 泛型？

Question

我在使用 Dagger 时遇到了一些奇怪的 kotlin 通用问题，我已经解决了一些问题，但解决方案并不完善。

这是匕首类：

@Module class P5Module {
    @Provides fun pool(): RecyclerView.RecycledViewPool = RecyclerView.RecycledViewPool()
    @Provides
    fun adapters(fusion: P5FusionAdapter, personas: P5ListAdapter, skills: P5SkillsAdapter, info: InfoAdapter)
            : List<Pageable> = listOf(fusion, personas, skills, info)
}

@ActivityScope
@Subcomponent(modules = arrayOf(P5Module::class)) interface P5Component {
    fun adapter(): PageableAdapter
}

interface Pageable {
    fun manager(ctx: Context): LayoutManager
    fun attach()
    fun adapter(): Adapter<*>
}

class PageableAdapter
@Inject constructor(val pageables: List<Pageable>, val pool: RecyclerView.RecycledViewPool) :PagerAdapter()

当我构建时，我在*组件中得到这个 kapt 错误：

e: C:\Users\daykm\StudioProjects\P5Executioner\app\build\tmp\kapt3\stubs\appDebug\com\daykm\p5executioner\AppComponent.java:17: error: [com.daykm.p5executioner.main.P5Component.adapter()] java.util.List<? extends com.daykm.p5executioner.view.Pageable> cannot be provided without an @Provides-annotated method.
e: 

e: public abstract interface AppComponent {
e:                 ^
e:       java.util.List<? extends com.daykm.p5executioner.view.Pageable> is injected at
e:           com.daykm.p5executioner.view.PageableAdapter.<init>(pageables, …)
e:       com.daykm.p5executioner.view.PageableAdapter is provided at
e:           com.daykm.p5executioner.main.P5Component.adapter()
e: java.lang.IllegalStateException: failed to analyze: org.jetbrains.kotlin.kapt3.diagnostic.KaptError: Error while annotation processing

我查看了生成的存根：

@javax.inject.Inject()
public PageableAdapter(@org.jetbrains.annotations.NotNull()
java.util.List<? extends com.daykm.p5executioner.view.Pageable> pageables, @org.jetbrains.annotations.NotNull()
android.support.v7.widget.RecyclerView.RecycledViewPool pool) {
    super();
}

@org.jetbrains.annotations.NotNull()
@dagger.Provides()
public final java.util.List<com.daykm.p5executioner.view.Pageable> adapters(@org.jetbrains.annotations.NotNull()

显然不匹配，因为当我像这样修改匕首类时：

@Module class P5Module {
    @Provides fun pool(): RecyclerView.RecycledViewPool = RecyclerView.RecycledViewPool()
    @Provides
    fun adapters(fusion: P5FusionAdapter, personas: P5ListAdapter, skills: P5SkillsAdapter, info: InfoAdapter)
            : List<*> = listOf(fusion, personas, skills, info)
}

@ActivityScope
@Subcomponent(modules = arrayOf(P5Module::class)) interface P5Component {
    fun adapter(): PageableAdapter
}

interface Pageable {
    fun manager(ctx: Context): LayoutManager
    fun attach()
    fun adapter(): Adapter<*>
}

class PageableAdapter
@Inject constructor(val pageables: List<*>, val pool: RecyclerView.RecycledViewPool) :PagerAdapter()

问题消失了。 我是否遇到了协变和逆变的一些奇怪的翻译问题？我宁愿不强迫下游演员。

Answer 1

默认情况下，Kotlin 的 List<out E> 转换为 Java 的 List<? extends E> 中的协方差。 Dagger 不喜欢那样。

要解决这个问题，您可以切换到不变的MutableList<E>，或者写成List<@JvmSuppressWildcards E>。