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

@Overridepublic 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();}