(7) Dependency between Dagger2 Component

Code example

If the PlaygroundComponentsyringe needs to ZooComponentprovide an object.

class Tiger {
    
    
    public void sleep() {
    
    
        System.out.println("Tiger sleeping");
    }
}
// 为注射器提供工厂类
// @Module: 表示Dagger2可以将该类当作对象工厂.
@Module
class ZooModule {
    
    
    // @Provides: 表示Dagger2可以调用providerTiger()方法为注射器提供对象.
    @Provides
    public Tiger providerTiger() {
    
    
        return new Tiger();
    }
}
// 注射器
// @Component: 该注解是用来创造对象提供方和对象使用间的桥梁,如何将对象赋值给成员变量都是由它来做的.
@Component(modules = {
    
    ZooModule.class})
interface ZooComponent {
    
    
    // 表示ZooComponent注射器可以向其他注射器提供ZooModule工厂类中的方法,也就是提供ZooModule工厂中创建的对象.
    Tiger providerTiger();
}

// 注射器
// dependencies: 表示PlaygroundComponent注射器依赖ZooComponent注射器,
// ZooComponent注射器向PlaygroundComponent注射器提供ZooModule工厂创建的Tiger对象.
@Component(dependencies = {
    
    ZooComponent.class})
interface PlaygroundComponent {
    
    
    Playground inject(Playground zoo);
}


// 对象使用者
public class Playground {
    
    
    // @Inject: 该注解用于成员变量上代表注射器可以为该成员变量赋值对象.
    @Inject
    Tiger tiger;

    @Test
    public void 案例七() {
    
    
        // 创建ZooComponent注射器对象
        ZooComponent zooComponent = DaggerZooComponent.create();
        // DaggerPlaygroundComponent注射器依赖ZooComponent注射器,所以使用zooComponent()将ZooComponent注射器对象传入DaggerPlaygroundComponent注射器中.
        // 创建好DaggerPlaygroundComponent对象之后调用inject()方法为Playground对象中注入Tiger对象.
        DaggerPlaygroundComponent.builder().zooComponent(zooComponent).build().inject(this);
        tiger.sleep();
    }
}

Dagger2 generated code reading

After analyzing the dependency between syringes, how can one syringe use objects in other syringes.

Looking at the code generated by Degger2 based on the above case, the generated code is in the build\generated\sources\annotationProcessor\..folder.

1. ZooComponentThe creation of the syringe object
   ZooComponentdepends onZooModule

final class DaggerZooComponent implements ZooComponent {
    
    
    private final ZooModule zooModule;
    public static ZooComponent create() {
    
    
        // 这里最终调用的是Builder.build(),然后回创建ZooComponent对象.
        return new Builder().build();
    }
    static final class Builder {
    
    
        private Builder() {
    
    
        }
        public ZooComponent build() {
    
    
            if (zooModule == null) {
    
    
              // 依赖的ZooModule对象在此处创建
              this.zooModule = new ZooModule();
            }
            // DaggerZooComponent在这里被创建,它持有zooModule引用,zooModule是一个工厂类,里面提供了创建Tiger对象的方法.
            return new DaggerZooComponent(zooModule);
        }
    }
}

2. DaggerPlaygroundComponentObject creation
   DaggerPlaygroundComponentdepends on DaggerZooComponentsyringe
   • DaggerPlaygroundComponent.builder()
DaggerPlaygroundComponentInner class Builderobject being created

      final class DaggerPlaygroundComponent implements PlaygroundComponent {
         
         
          public static Builder builder() {
         
         
              return new Builder();
          }
          static final class Builder {
         
         
              private Builder() {
         
         
              }
          }
      }
   

   • DaggerPlaygroundComponent.Builder.zooComponent(zooComponent)
     To DaggerPlaygroundComponent.Builderset the object zooComponentsyringe objects.

      final class DaggerPlaygroundComponent implements PlaygroundComponent {
         
         
          private ZooComponent zooComponent;
          static final class Builder {
         
         
              // 为Builder对象设置ZooComponent对象
              public Builder zooComponent(ZooComponent zooComponent) {
         
         
                this.zooComponent = Preconditions.checkNotNull(zooComponent);
                return this;
              }
          }
      }
   

   • DaggerPlaygroundComponent.Builder.build()
     Create DaggerPlaygroundComponentobject

      final class DaggerPlaygroundComponent implements PlaygroundComponent {
         
         
          static final class Builder {
         
         
              public PlaygroundComponent build() {
         
         
                  Preconditions.checkBuilderRequirement(zooComponent, ZooComponent.class);
                  // 创建DaggerPlaygroundComponent对象,它持有zooComponent引用
                  return new DaggerPlaygroundComponent(zooComponent);
              }
          } 
      }
   

3. As Playgroundobjects inject Tigerobjects
   DaggerPlaygroundComponent.inject(this)

final class DaggerPlaygroundComponent implements PlaygroundComponent {
    
    
    private final ZooComponent zooComponent;// ZooComponent注射器
    @Override
    public Playground inject(Playground zoo) {
    
    
        // playground被注入的容器
        return injectPlayground(zoo);
    }
    
    private Playground injectPlayground(Playground instance) {
    
    
        // zooComponent.providerTiger(): 获取Tiger对象,这个就是在zooComponent注射器中定义的接口方法.具体的实现在DaggerZooComponent类中.
        // Playground_MembersInjector.injectTiger(instance,tiger): 具体赋值操作在这个地方.
        Playground_MembersInjector.injectTiger(instance, Preconditions.checkNotNull(zooComponent.providerTiger(), "Cannot return null from a non-@Nullable component method"));
        return instance;
    }
}

4. How dependent syringe from the ZooComponentacquisition of Tigerobjects
   specific implementation in the DaggerZooComponentmiddle, DaggerZooComponentthe holding ZooModulefactory class.

final class DaggerZooComponent implements ZooComponent {
    
    
    private final ZooModule zooModule;
    @Override
    public Tiger providerTiger() {
    
    
      // 接着向下看  
      return ZooModule_ProviderTigerFactory.providerTiger(zooModule);
    }
}
public final class ZooModule_ProviderTigerFactory implements Factory<Tiger> {
    
    
    // instance代表ZooModule工厂对象
    // providerTiger()方法就是在ZooModule类中用户定义的方法了,该方法返回Tiger对象.
    public static Tiger providerTiger(ZooModule instance) {
    
    
      return Preconditions.checkNotNull(instance.providerTiger(), "Cannot return null from a non-@Nullable @Provides method");
    }
}

5. Playground_MembersInjector.injectTiger(instance, zooComponent.providerTiger())
   For the Playgroundobject desired field assignment instanceas Playgroundan object, zooComponent.providerTiger()the above analysis is used to create a tiger over an object.

public final class Playground_MembersInjector implements MembersInjector<Playground> {
    
    
    public static void injectTiger(Playground instance, Object tiger) {
    
    
      // 最终的赋值操作在这里
      instance.tiger = (Tiger) tiger;
    }
}

The only point to note about the dependency between syringes is that the dependent syringe needs to define an Tiger providerTiger()interface method to expose the Tigerobject it needs to provide to the syringe that it needs.In the case, an interface method is provided to expose the object.