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

android-viewmodel android-architecture-components dagger-2 android

0

Zar E Ahmer · 技术社区 · 5 年前

我正在注射 ViewModelProvider.Factory BaseActivity 如下

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)
    }
}

class MainViewModel @Inject constructor( private val alertStore: AlertStore)
    : BaseViewModel(){

    fun showDialog(){
        viewModelScope.launch {
            delay(4000)

            alertStore.showToast("Alert after 4 seconds.")
        }
    }
}

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()
}

class App : DaggerApplication() {

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

AppComponent.kt

@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
    }
}

AppModule.kt

@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
            }
        }
    }
}

@Module
abstract class ActivityBuilder {

    //@Scope("")
    @ContributesAndroidInjector ///(modules = {MainModelFactory.class})
    public abstract MainActivity bindMainActivity();
}

@模块

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

}

ViewModelKey.kt

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

为什么我必须附加 @注入构造函数 视图模型 请解释一下我们为什么需要

0 回复 | 直到 5 年前

1

Sergei Bubenshchikov 5 年前

当你使用 匕首机器人 DaggerActivity (及 DaggerFragment 对于碎片)。

class MainActivity : DaggerActivity() {

    @Inject
    lateinit var viewModel: MainViewModel
}

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

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

@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

图表

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

其他信息: Dagger & Android