Android 如果没有@Inject构造函数或@Provides注释构造函数，则无法提供ViewModel

问题已编辑

我正在向

BaseActivity

注入ViewModelProvider.Factory，如下所示

open class BaseActivity : DaggerAppCompatActivity() {

    @Inject
    lateinit var factories: ViewModelProvider.Factory

    inline fun <reified T : ViewModel> getViewModel(): T {
        return ViewModelProvider(this, factories).get(T::class.java)
    }
}

为什么在我当前的实现中需要这个@Inject构造函数

class MainActivity : BaseActivity() {

  private lateinit var viewModel: MainViewModel

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

    viewModel = getViewModel()
    viewModel.showDialog()
}

}

App.kt

class App : DaggerApplication() {

override fun applicationInjector(): AndroidInjector<out DaggerApplication> {
    return DaggerAppComponent.builder().addContext(this).build()
    }
}

@Component(
    modules = [
        AndroidInjectionModule::class,
        AppModule::class,
        ActivityBuilder::class,
        ViewModelInjector::class

    ]
)
@Singleton
interface AppComponent : AndroidInjector<App> {

    @Component.Builder
    interface Builder {

        fun addContext(@BindsInstance context: Context): Builder

        fun build(): AppComponent
    }
}

@Module
class AppModule {

    @Provides
    fun provideViewModelFactories(viewModels: Map<Class<out ViewModel>,
            @JvmSuppressWildcards Provider<ViewModel>>):
            ViewModelProvider.Factory {
        return object : ViewModelProvider.Factory {
            override fun <T : ViewModel?> create(modelClass: Class<T>): T {
                val factory = viewModels[modelClass]?.get() ?: error(
                    "No factory provided against ${modelClass.name}"
                )
                @Suppress("UNCHECKED_CAST")
                return factory as T
            }
        }
    }
}

@MapKey
@Retention(AnnotationRetention.SOURCE)
annotation class ViewModelKey(
    val value: KClass<out ViewModel>
)

ViewModelInjector.kt

class App : DaggerApplication() {

override fun applicationInjector(): AndroidInjector<out DaggerApplication> {
    return DaggerAppComponent.builder().addContext(this).build()
    }
}

@Component(
    modules = [
        AndroidInjectionModule::class,
        AppModule::class,
        ActivityBuilder::class,
        ViewModelInjector::class

    ]
)
@Singleton
interface AppComponent : AndroidInjector<App> {

    @Component.Builder
    interface Builder {

        fun addContext(@BindsInstance context: Context): Builder

        fun build(): AppComponent
    }
}

@Module
class AppModule {

    @Provides
    fun provideViewModelFactories(viewModels: Map<Class<out ViewModel>,
            @JvmSuppressWildcards Provider<ViewModel>>):
            ViewModelProvider.Factory {
        return object : ViewModelProvider.Factory {
            override fun <T : ViewModel?> create(modelClass: Class<T>): T {
                val factory = viewModels[modelClass]?.get() ?: error(
                    "No factory provided against ${modelClass.name}"
                )
                @Suppress("UNCHECKED_CAST")
                return factory as T
            }
        }
    }
}

@MapKey
@Retention(AnnotationRetention.SOURCE)
annotation class ViewModelKey(
    val value: KClass<out ViewModel>
)

@模块 公共抽象类ViewModelInjector{

@Binds
@IntoMap
@ViewModelKey(MainViewModel.class)
public abstract ViewModel providesMainViewModel(MainViewModel model);

}

ViewModelKey.kt

class App : DaggerApplication() {

override fun applicationInjector(): AndroidInjector<out DaggerApplication> {
    return DaggerAppComponent.builder().addContext(this).build()
    }
}

@Component(
    modules = [
        AndroidInjectionModule::class,
        AppModule::class,
        ActivityBuilder::class,
        ViewModelInjector::class

    ]
)
@Singleton
interface AppComponent : AndroidInjector<App> {

    @Component.Builder
    interface Builder {

        fun addContext(@BindsInstance context: Context): Builder

        fun build(): AppComponent
    }
}

@Module
class AppModule {

    @Provides
    fun provideViewModelFactories(viewModels: Map<Class<out ViewModel>,
            @JvmSuppressWildcards Provider<ViewModel>>):
            ViewModelProvider.Factory {
        return object : ViewModelProvider.Factory {
            override fun <T : ViewModel?> create(modelClass: Class<T>): T {
                val factory = viewModels[modelClass]?.get() ?: error(
                    "No factory provided against ${modelClass.name}"
                )
                @Suppress("UNCHECKED_CAST")
                return factory as T
            }
        }
    }
}

@MapKey
@Retention(AnnotationRetention.SOURCE)
annotation class ViewModelKey(
    val value: KClass<out ViewModel>
)

@MapKey
@保留（AnnotationRetention.SOURCE）
注释类ViewModelKey(
val值：KClass
)

为什么我必须将@injectconstructor附加到每个ViewModel中，并请解释一下为什么我们需要@Binds@IntoMap，当你使用dagger android时，你应该将你的活动和片段作为

DaggerActivity

（对于碎片，

DaggerFragment

）

接下来，您应该为注入准备基础架构：

为您的每项活动创建注射器：

// All your injectors can be defined in this module
@Module(includes = [AndroidInjectionModule::class])
interface AppInjectorModule {

    @ContributesAndroidInjector(modules = [MainActivityVmModule::class, /*other dependecies*/])
    fun getMainActivityInjector(): MainActivity
}

创建模块以提供视图模型（一个活动可以有多个）和工厂模型

@Module(includes = [VmFactoryModule::class])
abstract class MainActivityVmModule {

    // bind implementation of ViewModel into map for ViewModelFactory
    @Binds
    @IntoMap
    @ClassKey(MainViewModelImpl::class)
    abstract fun bindMainVm(impl: MainViewModelImpl): ViewModel

    @Module
    companion object {
        @Provides
        @JvmStatic
        fun getMainVm(activity: MainActivity, factory: ViewModelProvider.Factory): MainViewModel {
            // create MainViewModelImpl in scope of MainActivity and inject dependecies by ViewModelFactory
            return ViewModelProviders.of(activity, factory)[MainViewModelImpl::class.java]
        }
    }
}

工厂可提供不同的模块，以避免重复

@Module
interface VmFactoryModule {

    @Binds
    // bind your implementation of factory
    fun bindVmFactory(impl: ViewModelFactory): ViewModelProvider.Factory
}

将活动添加到

AppComponent

图形

@Component(
    modules = [
        AppInjectorModule::class
    ]
)
@Singleton
interface AppComponent : AndroidInjector<App>

@组件(
模块=[
AppInjectorModule:：类
]
)
@独生子女
接口AppComponent:AndroidJector
请解释MainActivityVmModule以及@Binds、IntoMap和ClassKey。为什么我们不在注入活动或片段中使用，而在为ViewModel添加注释。请看我更新的问题，它现在运行良好。但我的概念不正确clear@XarEAhmer使用
@Binds
接近匕首时r创建依赖项（Vm）自动，但您应该在构造函数上设置注释
@Inject
。您应该明确地说dagger应该使用哪个构造函数来创建Vm和注入依赖项。您还可以通过模块的方法使用
@手动创建依赖项提供注释并通过setter设置依赖项（不推荐）：
@提供有趣的getVm（活动：活动，依赖项：VmDependency）：ViewModel=ViewModelProviders.of（活动）[MainViewModelImpl:：class.java]。应用{this.dependency=dependency}