Dagger 2 循环注射

Question

我有两个单例 class 我想将它们注入到 Fragments、Activites 等中，但我也必须将它们相互注入。那时我总是得到 SO 错误。

public class AdverticumChecker implements IAdverticumChecker {

    @Inject BannerManager bannerManager;

    public AdverticumChecker(Context context) {
        IndexApplication.getApplication().getAppComponent().inject(this);
    }
}

public class BannerManager {
    @Inject IAdverticumChecker adverticumChecker;

    public BannerManager(){
        IndexApplication.getApplication().getAppComponent().inject(this);
    }
}

这些是模块

@Module
public class BannerManagerModule {

        @Singleton
        @Provides
        BannerManager provideBannerManager(){
            return new BannerManager();
        }
    }

@Module
public class AdverticumCheckerModule {
    private Context context;

    public AdverticumCheckerModule(Context context){
        this.context = context;
    }

    @Singleton
    @Provides
    IAdverticumChecker provideAdverticumChecker(){
        return new AdverticumChecker(context);
    }
}

我在应用程序 class 中构建了一次图表。这是错误：

FATAL EXCEPTION: main java.lang.WhosebugError at com.aff.index.adverticum.AdverticumChecker_MembersInjector.injectMembers(AdverticumChecker_MembersInjector.java:38) at com.aff.index.adverticum.AdverticumChecker_MembersInjector.injectMembers(AdverticumChecker_MembersInjector.java:8) at com.aff.index.dagger.DaggerAppComponent.inject(DaggerAppComponent.java:679) at com.aff.index.adverticum.AdverticumChecker.(AdverticumChecker.java:50) at com.aff.index.dagger.AdverticumCheckerModule.provideAdverticumChecker(AdverticumCheckerModule.java:30) at com.aff.index.dagger.AdverticumCheckerModule_ProvideAdverticumCheckerFactory.get(AdverticumCheckerModule_ProvideAdverticumCheckerFactory.java:24) at com.aff.index.dagger.AdverticumCheckerModule_ProvideAdverticumCheckerFactory.get(AdverticumCheckerModule_ProvideAdverticumCheckerFactory.java:8) at dagger.internal.DoubleCheck.get(DoubleCheck.java:46) at com.aff.index.adverticum.BannerManager_MembersInjector.injectMembers(BannerManager_MembersInjector.java:67) at com.aff.index.adverticum.BannerManager_MembersInjector.injectMembers(BannerManager_MembersInjector.java:11) at com.aff.index.dagger.DaggerAppComponent.inject(DaggerAppComponent.java:704) at com.aff.index.adverticum.BannerManager.(BannerManager.java:89) at com.aff.index.dagger.BannerManagerModule.provideBannerManager(BannerManagerModule.java:21) at com.aff.index.dagger.BannerManagerModule_ProvideBannerManagerFactory.get(BannerManagerModule_ProvideBannerManagerFactory.java:24) at com.aff.index.dagger.BannerManagerModule_ProvideBannerManagerFactory.get(BannerManagerModule_ProvideBannerManagerFactory.java:8) at dagger.internal.DoubleCheck.get(DoubleCheck.java:46) at com.aff.index.adverticum.AdverticumChecker_MembersInjector.injectMembers(AdverticumChecker_MembersInjector.java:39) at com.aff.index.adverticum.AdverticumChecker_MembersInjector.injectMembers(AdverticumChecker_MembersInjector.java:8) at com.aff.index.dagger.DaggerAppComponent.inject(DaggerAppComponent.java:679)

Answer 1

首先，这...

@Singleton
@Provides
IAdverticumChecker provideAdverticumChecker(){
    return new AdverticumChecker(context);
}
...
public AdverticumChecker(Context context) {
    IndexApplication.getApplication().getAppComponent().inject(this);
}

绕过 DI 代表什么，基本上是注入依赖项，而不是让构造函数中的某些静态访问器神奇地注入它们 - 这种方式 AdvertiumChecker 几乎无法测试！将所有依赖项列为构造函数参数，并像这样执行：

@Singleton
@Provides
IAdverticumChecker provideAdverticumChecker(BannerManager bannerManager){
    return new AdverticumChecker(bannerManager);
}
...
private BannerManager mBannerManager;
public AdverticumChecker(BannerManager bannerManager) {
    mBannerManager = bannerManager;
}

Dagger 会自动为您填补此处的空白并构建合适的图形。

其次，如果 BannerManager 的构造依赖于 IAdvertiumChecker 的实例，你显然有一个 Dagger 会出错的循环依赖。通常这听起来像是糟糕的设计，但有时它并没有不同的做法，以防您在运行时需要一些东西。

在这些情况下，使用 Lazy 注入，即

@Inject
Lazy<BannerManager> mLazyBannerManager;
...
mLazyBannerManager.get().doSomething();

或

IAdvertiumChecker providerAdvertiumChecker(Lazy<BannerManager> lazyBannerManager) {
    return new AdverticumChecker(lazyBannerManager);
}

希望这对您有所帮助。

Dagger 2 循环注射

Dagger 2 cycle injection

java

android

dependency-injection

stack-overflow

dagger-2