Dagger2生成代码解析

╰半橙微兮° 2023-10-16 23:19 14阅读 0赞

## Dagger2生成代码解析 ##

根据[一个简单的Dagger2示例程序][Dagger2]，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 ###

![Dagger2\_UML][Dagger2_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();
    }

[Dagger2]: http://download.csdn.net/detail/ethanco/9473590
[Dagger2_UML]: https://img-blog.csdn.net/20160327110249654