Java Dagger 2-提供具有自己依赖项的方法

我正在努力理解和实施匕首2。我已经阅读了很多不同的教程和官方指南。我想我大体上理解了它，但我仍然不能理解一些简单的观点（虽然我写了它，但我已经找到了一些解决方案，但是..）：

@Provides方法可能有自己的依赖项

什么时候可能？

我所看到的可能是“组件包含一个依赖循环”

有没有人能帮助我了解可能的情况和不可能的情况。

---

谢谢。

经过漫长的实验，我找到了答案。 我把这个答案作为自己的提示卡，希望它能帮助其他匕首绝地

所以我们有匕首结构

• 雄激素应用
• 基本活动
• 导航器
• 应用程序组件
• 应用程序模块

ApplicationComponent.class

 @Singleton 
 @Component(modules = ApplicationModule.class)
 public interface ApplicationComponent {
     void inject(BaseActivity baseActivity);

     Navigator navigator();
     Context context();
     //...
 }

 @Singleton 
 @Component(modules = ApplicationModule.class)
 public interface ApplicationComponent {
     void inject(BaseActivity baseActivity);

     BaseNavigator navigator(); // changed to interface type
     Context context();
     //...
 }

ApplicationModule.class

@Module
public class ApplicationModule {
    private final AndroidApplication application;

    public ApplicationModule(AndroidApplication application) {
        this.application = application;
    }

    @Provides
    @Singleton
    Navigator provideNavigator() {
        return new Navigator();
    }

    @Provides
    @Singleton
    Context provideApplicationContext() {
        return this.application;
    }

}

@Module
public class ApplicationModule {
    private final AndroidApplication application;

    public ApplicationModule(AndroidApplication application) {
        this.application = application;
    }

    @Provides
    @Singleton
    BaseNavigator provideNavigator(Navigator navigator) {
        return navigator;
    } // this will return interface type but with implementation you needed

    @Provides
    @Singleton
    Context provideApplicationContext() {
        return this.application;
    }

}

导航器类

@Singleton
public class Navigator implements BaseNavigator {

    public Navigator() {}

}

@Singleton
public class Navigator implements BaseNavigator {

    @Inject // don't forget to add this annotation to the constructor
    public Navigator() {}

}

基本活动类

public abstract class BaseActivity extends Activity {

    @Inject
    Navigator navigator;

    //code here

}

public abstract class BaseActivity extends Activity {

    @Inject
    BaseNavigator navigator;// changed to interface type

    //code here

}

此代码将正常工作，BaseActivity将以ApplicationModule提供的新navigator（）的形式获取navigator

但是，如果您有几个BaseNavigator类的实现，您可以获得一些特定的实现，例如Navigator类，而无需手动创建新实例

*此构造将为您提供“组件包含依赖循环”

---

您可以这样做：

ApplicationComponent.class

 @Singleton 
 @Component(modules = ApplicationModule.class)
 public interface ApplicationComponent {
     void inject(BaseActivity baseActivity);

     Navigator navigator();
     Context context();
     //...
 }

 @Singleton 
 @Component(modules = ApplicationModule.class)
 public interface ApplicationComponent {
     void inject(BaseActivity baseActivity);

     BaseNavigator navigator(); // changed to interface type
     Context context();
     //...
 }

ApplicationModule.class

@Module
public class ApplicationModule {
    private final AndroidApplication application;

    public ApplicationModule(AndroidApplication application) {
        this.application = application;
    }

    @Provides
    @Singleton
    Navigator provideNavigator() {
        return new Navigator();
    }

    @Provides
    @Singleton
    Context provideApplicationContext() {
        return this.application;
    }

}

@Module
public class ApplicationModule {
    private final AndroidApplication application;

    public ApplicationModule(AndroidApplication application) {
        this.application = application;
    }

    @Provides
    @Singleton
    BaseNavigator provideNavigator(Navigator navigator) {
        return navigator;
    } // this will return interface type but with implementation you needed

    @Provides
    @Singleton
    Context provideApplicationContext() {
        return this.application;
    }

}

导航器类

@Singleton
public class Navigator implements BaseNavigator {

    public Navigator() {}

}

@Singleton
public class Navigator implements BaseNavigator {

    @Inject // don't forget to add this annotation to the constructor
    public Navigator() {}

}

基本活动类

public abstract class BaseActivity extends Activity {

    @Inject
    Navigator navigator;

    //code here

}

public abstract class BaseActivity extends Activity {

    @Inject
    BaseNavigator navigator;// changed to interface type

    //code here

}

---

现在您没有为Navigator创建新的实例，Dagger在其生成的工厂中代替了您创建了它。

实际上，您可以使用限定符（

@Named（“something”）

注释）为给定的依赖项获取多种不同类型的实现

 @Singleton 
 @Component(modules = ApplicationModule.class)
 public interface ApplicationComponent {
     void inject(BaseActivity baseActivity);

     @Named("first")
     BaseNavigator firstNavigator();
     @Named("second")
     BaseNavigator secondNavigator();

     Context context();
     //...
 }

@Module
public class ApplicationModule {
    private final AndroidApplication application;

    public ApplicationModule(AndroidApplication application) {
        this.application = application;
    }

    @Provides
    @Singleton
    @Named("first")
    BaseNavigator provideFirstNavigator() {
        return new SomeNavigator();
    }

    @Provides
    @Singleton
    @Named("second")
    BaseNavigator provideSecondNavigator() {
        return new OtherNavigator();
    }

    @Provides
    Context provideApplicationContext() {
        return this.application;
    }

}

public abstract class BaseActivity extends Activity {

    @Inject
    @Named("second")
    BaseNavigator navigator;

---

Navigator provideNavigator（Navigator-Navigator）{

当然，它包含一个循环。provider方法需要它自己的结果作为依赖项，这将是一个递归方法调用。如果需要提供

Navigator

字段，则应该将其提供给模块本身（尽管我不明白为什么），或者您不应该将其指定为提供程序方法的参数。但是我想如果您想要实现的是使用

@Inject

带注释的构造函数将实例化移出模块，那么我想这是可行的。