Dagger 2.0构造函数注入和Singleton

Question

是否可以一次使用Dagger 2.0构造函数注入和单例.我在文档中找不到答案.

例:

@Singleton
public class MyClass {
   private final OtherClass member;

   @Inject
   public MyClass(OtherClass member){
        this.member = member;
   }
 }

构造函数注入确实有效.但是,如果我在课堂上编写@Singleton,是否可以保证MyClass是作为单身人士创建的？

谢谢

Answer 1

是.

由于Dagger 2为您生成源代码,因此很容易检查发生了什么.例如,将以下模块与您的组合使用时MyClass:

@Component
@Singleton
public interface MyComponent {
  MyClass myClass();
}

生成以下实现:

@Generated("dagger.internal.codegen.ComponentProcessor")
public final class DaggerMyComponent implements MyComponent {
  private Provider<MyClass> myClassProvider;

  private DaggerMyComponent(Builder builder) {  
    assert builder != null;
    initialize(builder);
  }

  public static Builder builder() {  
    return new Builder();
  }

  public static MyComponent create() {  
    return builder().build();
  }

  private void initialize(final Builder builder) {  
    this.myClassProvider = ScopedProvider.create(MyClass_Factory.create(OtherClass_Factory.create()));
  }

  @Override
  public MyClass myClass() {  
    return myClassProvider.get();
  }

  public static final class Builder {
    private Builder() {  
    }

    public MyComponent build() {  
      return new DaggerMyComponent(this);
    }
  }
}

在initialize(Builder),您可以看到a ScopedProvider用作Providerfor MyClass.当调用myClass()的方法,所述ScopedProvider的get()方法被调用,其作为一个单实现的:

public T get() {
  // double-check idiom from EJ2: Item 71
  Object result = instance;
  if (result == UNINITIALIZED) {
    synchronized (this) {
      result = instance;
      if (result == UNINITIALIZED) {
        instance = result = factory.get();
      }
    }
  }
  return (T) result;
}