Question

我实现了自定义ViewModelFactory，Dagger DI对ViewModel的成员进行了自动注入，所有代码如下：

class ViewModelFactory @Inject constructor(
    private val creators: Map<Class<out ViewModel>, @JvmSuppressWildcards Provider<ViewModel>>
): ViewModelProvider.Factory {

    override fun <T : ViewModel?> create(modelClass: Class<T>): T {
        val creator = creators[modelClass] ?: creators.entries.firstOrNull {
            modelClass.isAssignableFrom(it.key)
        }?.value ?: throw IllegalArgumentException("unknown model class $modelClass")

        try {
            @Suppress("UNCHECKED_CAST")
            return creator.get() as T
        } catch (e: Exception) {
            throw RuntimeException(e)
        }
    }
}

DI：

@Suppress("unused")
@Module
abstract class ViewModelModule {

    @Binds
    abstract fun bindViewModelFactory(factory: ViewModelFactory): ViewModelProvider.Factory
}

@Singleton
@Component(
    modules = [
        AndroidInjectionModule::class,
        AppModule::class,
        ViewModelModule::class,
        ActivityModule::class
    ]
)
interface AppComponent: AndroidInjector<App> {

    @Component.Builder
    abstract class Builder: AndroidInjector.Builder<App>()
}

@Suppress("unused")
@Module
abstract class ActivityModule {
    @ContributesAndroidInjector(
        modules = [LoginFragmentBuilderModule::class, LoginViewModelModule::class]
    )
    abstract fun contributeLoginActivity(): LoginActivity

    @ContributesAndroidInjector(modules = [])
    abstract fun contributeMainActivity(): MainActivity
}

@Suppress("unused")
@Module
abstract class LoginViewModelModule {

    @Binds
    @IntoMap
    @ViewModelKey(AccountViewModel::class)
    abstract fun bindAccountViewModel(accountViewModel: AccountViewModel): ViewModel
}

@Suppress("unused")
@Module
abstract class LoginFragmentBuilderModule {

    @ContributesAndroidInjector
    abstract fun contributeAccountFragment(): AccountFragment
}

@Module
object AppModule {

    @JvmStatic
    @Provides
    fun provideGitHubApi(retrofit: Retrofit): IGitHubApi {
        return retrofit.create(IGitHubApi::class.java)
    }

    // A lot of other providers
}

AccountViewModel：：

class AccountViewModel(app: Application) : AndroidViewModel(app) {

    @Inject
    lateinit var gitHubApi: IGitHubApi
}

我使用tutorial编写了它，但是编译时出现了错误：

e: /test/di/AppComponent.java:8: error: [Dagger/MissingBinding] [dagger.android.AndroidInjector.inject(T)] test.ui.login.models.AccountViewModel cannot be provided without an @Inject constructor or an @Provides-annotated method. This type supports members injection but cannot be implicitly provided.
public abstract interface AppComponent extends dagger.android.AndroidInjector<com.contedevel.juke.App> {
                ^
      test.ui.login.models.AccountViewModel is injected at
          test.di.LoginViewModelModule.bindAccountViewModel(accountViewModel)

      java.util.Map<java.lang.Class<? extends androidx.lifecycle.ViewModel>,javax.inject.Provider<androidx.lifecycle.ViewModel>> is injected at
          test.di.ViewModelFactory.<init>(creators)
      test.di.ViewModelFactory is injected at
          test.di.ViewModelModule.bindViewModelFactory(factory)
      androidx.lifecycle.ViewModelProvider.Factory is injected at
          test.ui.login.AccountFragment.viewModelFactory
      test.ui.login.AccountFragment is injected at
          dagger.android.AndroidInjector.inject(T)
  component path: test.di.AppComponent → test.di.ActivityModule_ContributeLoginActivity.LoginActivitySubcomponent → test.di.LoginFragmentBuilderModule_ContributeAccountFragment.AccountFragmentSubcomponent

Answer 1

从堆栈跟踪中：

test.ui.login.models.AccountViewModel cannot be provided without an @Inject constructor or an @Provides-annotated method

您的AccountViewModel没有@Inject构造函数。

尝试一下：

class AccountViewModel @Inject constructor(
    private val gitHubApi: IGitHubApi, 
    app: Application) : AndroidViewModel(app) {
}

Answer 2

首先，在这种情况下Dagger将如何工作。您正在通过AccountViewModel中的参数绑定bindAccountViewModel的实例。但是，现在匕首将创建AccountViewModel的实例，并将其绑定到键为AccountViewModel::class的Map。

根据堆栈跟踪，Dagger建议您可以使用构造函数注入，也可以在模块中使用Provides方法提供ViewModel。从我们当前的实现中，第二个建议变得很普遍，因为我们没有创建AccountViewModel实例。因此，您需要在AccountViewModel中将IGithubApi作为构造函数参数传递，这在这种情况下将是可行的解决方案。

class AccountViewModel @Inject constructor(private val api: IGithubAPI, app: Application) : AndroidViewModel(app)

Dagger无法注入ViewModel的成员

2 个答案: