Dagger2生成代码解析

Dagger2生成代码解析

根据一个简单的Dagger2示例程序，进行进一步的探索，对Dagger2自动生成的代码进行解析。以下解析都基于该Demo生成的类进行。

UML

DaggerActivityComponent.Builder类

作用: 生成该类的父类 (DaggerActivityComponent)

public static final class Builder {
private ActivityModule activityModule;

    private Builder() {  
    }

    /*
     * 生成Component实现类
     */
    public ActivityComponent build() {  
      if (activityModule == null) {
        this.activityModule = new ActivityModule();
      }
      return new DaggerActivityComponent(this); //Component:被装饰的类
    }

    /*
    * 设置Module
    */
    public Builder activityModule(ActivityModule activityModule) {  
      if (activityModule == null) {
        throw new NullPointerException("activityModule");
      }
      this.activityModule = activityModule;
      return this;
    }
 }  

DaggerActivityComponent

作用: 初始化Provider，MembersInjector，关联Activity和Module，进行注入

@Generated("dagger.internal.codegen.ComponentProcessor")
public final class DaggerActivityComponent implements ActivityComponent {
  private Provider<Person> provideUserModelProvider;
  private MembersInjector<MainActivity> mainActivityMembersInjector;

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

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

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

/*
 * 进行初始化
 */
  private void initialize(final Builder builder) {  
    this.provideUserModelProvider = ActivityModule_ProvideUserModelFactory.create(builder.activityModule);
    this.mainActivityMembersInjector = MainActivity_MembersInjector.create((MembersInjector) MembersInjectors.noOp(), provideUserModelProvider);
  }

/*
 * 进行注入
 */
  @Override
  public void inject(MainActivity activity) {  
    mainActivityMembersInjector.injectMembers(activity);
  }

  public static final class Builder {
    ...
  }
}

ActivityModule_ProvideUserModelFactory

Provides工厂，根据ActivityModule获取Person

@Generated("dagger.internal.codegen.ComponentProcessor")
public final class ActivityModule_ProvideUserModelFactory implements Factory<Person> {
  private final ActivityModule module;

  public ActivityModule_ProvideUserModelFactory(ActivityModule module) {  
    assert module != null;
    this.module = module;
  }

  @Override
  public Person get() {  
    Person provided = module.provideUserModel();
    if (provided == null) {
      throw new NullPointerException("Cannot return null from a non-@Nullable @Provides method");
    }
    return provided;
  }

  public static Factory<Person> create(ActivityModule module) {  
    return new ActivityModule_ProvideUserModelFactory(module);
  }
}  

MainActivity_MembersInjector

作用:对@Inject注释的变量进行赋值

@Generated("dagger.internal.codegen.ComponentProcessor")
public final class MainActivity_MembersInjector implements MembersInjector<MainActivity> {
  private final MembersInjector<AppCompatActivity> supertypeInjector;
  private final Provider<Person> personProvider;

  public MainActivity_MembersInjector(MembersInjector<AppCompatActivity> supertypeInjector, Provider<Person> personProvider) {  
    assert supertypeInjector != null;
    this.supertypeInjector = supertypeInjector;
    assert personProvider != null;
    this.personProvider = personProvider;
  }

  @Override
  public void injectMembers(MainActivity instance) {  
    if (instance == null) {
      throw new NullPointerException("Cannot inject members into a null reference");
    }
    supertypeInjector.injectMembers(instance);
    instance.person = personProvider.get(); //赋值给MainActivity.person
  }

  public static MembersInjector<MainActivity> create(MembersInjector<AppCompatActivity> supertypeInjector, Provider<Person> personProvider) {  
      return new MainActivity_MembersInjector(supertypeInjector, personProvider);
  }
}

多层依赖的情况

在多层依赖的情况下，最大的改变只是在MembersInjector的injectMembers中赋值部分添加了赋值的语句

@Override
public void injectMembers(MainActivity instance) {  
    if (instance == null) {
      throw new NullPointerException("Cannot inject members into a null reference");
    }
    supertypeInjector.injectMembers(instance);
    //以下为多层依赖情况下的赋值
    instance.person = personProvider.get(); 
    instance.shoppingCart = shoppingCartProvider.get();
}