java–Dagger– 从其他类访问Singleton对象

概述我一直在努力理解并设置Dagger来处理Android项目的依赖注入.我的单一(没有双关语)目标是创建我可以在我的应用程序中访问的单例对象.我已经在初始活动中成功设置了对象.我被困在哪里是从其他类访问这些对象.这是我到目前为止的设置：初始App活动publicclassSplashScreenActivity

我一直在努力理解并设置Dagger来处理Android项目的依赖注入.我的单一(没有双关语)目标是创建我可以在我的应用程序中访问的单例对象.我已经在初始活动中成功设置了对象.我被困在哪里是从其他类访问这些对象.这是我到目前为止的设置：

初始App活动

public class SplashScreenActivity extends AppCompatActivity {    @Inject SessionKeyExchangerService exchangerService;    @OverrIDe    protected voID onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentVIEw(R.layout.activity_splash_screen);        AppComponent component = DaggerAppComponent.builder().appModule(new AppModule()).build();        // establish the session ID as a singleton object        exchangerService = component.provIDeSessionKeyExchangerService();        // test whether I can access the singleton from another class        exchangerService.sendEncryptedKeyToServer();    } 

组件类

@Singleton@Component(modules = {AppModule.class})public interface AppComponent {    SessionKeyExchangerService provIDeSessionKeyExchangerService();    AESCipherService provIDeCipherService();}

模块类

@Modulepublic class AppModule {    @ProvIDes @Singleton    AESCipherService provIDeCipherService() {        return new AESCipherService();    }    @ProvIDes @Singleton    SessionKeyExchangerService provIDeSessionKeyExchangerService(AESCipherService service) {        return new SessionKeyExchangerService(service);    }}

AESCipherService

public class AESCipherService {    private Long sessionID;    public AESCipherService() {        sessionID = makeSessionID();        Log.d(Constants.TAG, "Session ID: " + Long.toString(sessionID));    }    private Long makeSessionID() {        // this generates a random unsigned integer in the space {0, 2^32-1)        Random random = new Random();        return random.nextLong() & 0xffffffffL;    }    public Long getSessionID() {        return sessionID;    }}

SessionKeyExchanger类

public class SessionKeyExchangerService {    private static SessionKeyExchangerService exchanger;    private AESCipherService cipherService;    @Inject    public SessionKeyExchangerService(AESCipherService cipherService) {        this.cipherService = cipherService;    }    public voID sendEncryptedKeyToServer () {        // the next line is almost certainly part of the problem        // but I don't kNow how to fix!!!        AppComponent component = DaggerAppComponent.builder().appModule(new AppModule()).build();        AESCipherService cipherService = component.provIDeCipherService();        Long sessionID = cipherService.getSessionID();        Log.d(Constants.TAG, "singleton verification: " + (Long.toString(sessionID)));    }

这是一些示例输出：

Session ID: 217186720
singleton verification: 790090968

显然,我没有访问同一个对象.我意识到至少部分问题源于我在尝试获取对AppComponent类的引用时在AESCipherService中调用new运算符的方式,但我不知道如何获取此引用另一种方式.

我该如何解决？谢谢！

解决方法:

 AppComponent component = DaggerAppComponent.builder().appModule(new AppModule()).build();

Nononononono.这不会是一个单身人士.范围提供程序仅适用于每个组件,这意味着您必须在整个应用程序中使用单个组件,以使@Singleton范围内的模块实际共享同一范围提供程序.在这种情况下,您每次创建活动时都会创建一个新组件.

你需要像这样创建它们：

public enum Injector {    INSTANCE;    private AppComponent appComponent;    static {        INSTANCE.appComponent = DaggerAppComponent.create();    }    public getAppComponent() {        return appComponent;    }}

你也可以子类化Application并在onCreate()中创建一个.

也

@Singleton@Component(modules = {AppModule.class})public interface AppComponent {    SessionKeyExchangerService provIDeSessionKeyExchangerService();    AESCipherService provIDeCipherService();    voID inject(SplashScreenActivity splashScreenActivity); //does NOT support base class injection! Concrete classes only!}

然后

public class SplashScreenActivity extends AppCompatActivity {    @Inject SessionKeyExchangerService exchangerService;    @OverrIDe    protected voID onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentVIEw(R.layout.activity_splash_screen);        Injector.INSTANCE.getAppComponent().inject(this);        // establish the session ID as a singleton object        // exchangerService = component.provIDeSessionKeyExchangerService(); //totally not needed        // test whether I can access the singleton from another class        exchangerService.sendEncryptedKeyToServer();

此外,您正在使用基于@ Module的实例创建,因此在构造函数中丢失@Inject

@Injectpublic SessionKeyExchangerService(AESCipherService cipherService) {    this.cipherService = cipherService;}

并且

public voID sendEncryptedKeyToServer () {    // the next line is almost certainly part of the problem    // but I don't kNow how to fix!!!    //AppComponent component = DaggerAppComponent.builder().appModule(new AppModule()).build(); //you don't need this here at all    //AESCipherService cipherService = component.provIDeCipherService(); //already provIDed in constructor

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