从Dagger2迁移到Hilt：如何迁移带自定义Component.Factory的应用组件

问题背景 #

将遗留应用从Dagger2迁移到Hilt时，原ApplicationComponent通过Factory绑定多个实例并依赖子组件，转为EntryPoint后无法处理Factory中的额外内容，具体代码如下：

原ApplicationComponent代码

abstract class ApplicationComponent : ApplicationDependencies {

    abstract fun inject(application: MyApp)

    @Component.Factory
    interface Factory {
        fun applicationComponent(
            @BindsInstance myApp: MyApp,
            @BindsInstance sharedPreferences: SharedPreferences,
            @BindsInstance activeActivityProvider: ActiveActivityProvider,
            @BindsInstance appLifecycleObservable: Observable<ApplicationStateEvent>,
            @BindsInstance @EnvironmentName
            environmentName: String,
            schedulersComponent: SchedulerComponent,
            commonComponent: CommonComponent,
        ): ApplicationComponent
    }
}

原MyApp初始化代码

public class MyApp extends Application {
    private ApplicationComponent component;
    // ... 定义 appLifecyleObserver 等逻辑

    public void onCreate() {
        ProcessLifecycleOwner.get().getLifecycle().addObserver(appLifecycleObserver);
        super.onCreate();
        
        // ... 初始化 mSharedPreferences、environmentName 等逻辑

        component = DaggerApplicationComponent.factory().applicationComponent(
                this,
                mSharedPreferences,
                activeActivityProvider,
                appLifecycleRelay,
                environmentName,
                DaggerSchedulersComponent.create(),
                DaggerCommonComponent.factory().commonComponent(this),
        );
        component.inject(this);
    }
}

迁移方案 #

Hilt没有直接对应Dagger Component.Factory的概念，需将Factory中的参数拆分处理：

1. 处理@BindsInstance绑定的实例

   • MyApp实例：在MyApp上添加@HiltAndroidApp注解，Hilt自动绑定Application/MyApp类型，无需手动传入。
   • 其余绑定实例（SharedPreferences、ActiveActivityProvider等）：创建Hilt单例模块，通过@Provides方法提供实例，复用原初始化逻辑：

     @Module
     @InstallIn(SingletonComponent::class)
     object AppBindingsModule {
         @Provides
         @Singleton
         fun provideSharedPreferences(app: MyApp): SharedPreferences {
             // 复用原代码中初始化mSharedPreferences的逻辑
             return app.getSharedPreferences("app_prefs", Context.MODE_PRIVATE)
         }
     
         @Provides
         @Singleton
         @EnvironmentName
         fun provideEnvironmentName(app: MyApp): String {
             // 复用原代码中获取environmentName的逻辑
             return app.environmentName
         }
     
         @Provides
         @Singleton
         fun provideActiveActivityProvider(): ActiveActivityProvider {
             // 原代码中初始化该实例的逻辑
             return ActiveActivityProviderImpl()
         }
     
         @Provides
         @Singleton
         fun provideAppLifecycleObservable(app: MyApp): Observable<ApplicationStateEvent> {
             // 复用原appLifecycleRelay的逻辑
             return app.appLifecycleRelay
         }
     }
     

2. 处理依赖的子组件（SchedulerComponent、CommonComponent）

   • 将子组件转为Hilt模块，把原组件提供的依赖移到@InstallIn(SingletonComponent::class)的模块中：
     • 无依赖的SchedulerComponent：直接在模块中提供对应依赖
     • 依赖MyApp的CommonComponent：在@Provides方法中注入MyApp复用逻辑
       示例：

     @Module
     @InstallIn(SingletonComponent::class)
     object CommonModule {
         @Provides
         @Singleton
         fun provideCommonDependency(app: MyApp): CommonDependency {
             // 复用原CommonComponent中提供该依赖的逻辑
             return CommonDependencyImpl(app)
         }
     }
     

3. 替换原Component注入逻辑

   • 在MyApp上添加@HiltAndroidApp注解，Hilt自动生成SingletonComponent替代原ApplicationComponent
   • 移除原component变量及手动初始化代码，Hilt自动完成注入；若需在MyApp中获取依赖，定义EntryPoint：

     @HiltAndroidApp
     public class MyApp extends Application {
         // ... 保留appLifecyleObserver等逻辑
     
         @Override
         public void onCreate() {
             ProcessLifecycleOwner.get().getLifecycle().addObserver(appLifecycleObserver);
             super.onCreate();
             // 移除原component初始化代码
         }
     
         // 定义EntryPoint用于获取依赖
         @EntryPoint
         @InstallIn(SingletonComponent.class)
         interface AppEntryPoint {
             SharedPreferences getSharedPreferences();
             // 其他需要暴露的依赖
         }
     }
     

4. 替换原inject方法
   原ApplicationComponent的inject(MyApp)方法无需保留，只需在MyApp中需要注入的字段上添加@Inject注解，Hilt自动完成注入。

内容的提问来源于stack exchange，提问作者Jenny Zeng