分析的原始碼是基於Android Dagger2（一） 基本使用 的例子來分析物件是如何被注入的. 如果還沒看上一篇文章, 可以先去看看.

在分析原始碼之前, 先理一理類與類之間的依賴關係 :

public class AddMenuBalanceFragment extends BaseFragment{
    @Inject
    AddMenu BalancePresenter presenter;
}

從上面的程式碼可以看出 AddMenuBalanceFragment需要注入AddMenuBalancePresenter

Dagger2要想注入AddMenuBalancePresenter

, 必須呼叫AddMenuBalancePresenter的構造方法:

public class AddMenuBalancePresenter implements AddMenuBalanceContract.Presenter {

    private final AddMenuBalanceContract.View mView;

    private final MenuBalanceRepository mMenuBalanceRepository;

    @Inject
    AddMenuBalancePresenter(AddMenuBalanceContract.View view, MenuBalanceRepository mMenuBalanceRepository) {
        this
 
.mView = view;
        this.mMenuBalanceRepository = mMenuBalanceRepository;
    }
}

而AddMenuBalancePresenter的構造方法又依賴View和MenuBalanceRepository, 這裡的View就是Activity或者Fragment, 這個不能是我們new出來的,因為所有的介面都是由Android系統來建立和銷燬的. 所以這個引數只能我們通過傳遞引數的方式傳遞給Dagger2.

要想提供MenuBalanceRepository Dagger2就必須要呼叫MenuBalanceRepository

的構造方法 :

@Singleton
public class MenuBalanceRepository implements IMenuBalanceSource {

    private final IMenuBalanceSource remoteSource;

    @Inject
    MenuBalanceRepository(@Remote IMenuBalanceSource remoteSource) {
        this.remoteSource = remoteSource;
    }
}

發現MenuBalanceRepository的構造方法又依賴IMenuBalanceSource.

它們的依賴關係可以用下圖來表示:

通過面的圖得知, 只要把IMenuBalanceSource構造出來了, MenuBalanceRepository也就可以構造出來了, 如果MenuBalanceRepository和View都有了就可以把AddMenuBalancePresenter構造出來了.

這樣AddMenuBalanceFragment所需要的AddMenuBalancePresenter也就被注入了.

下面就分析下Dagger2生成的原始碼, 看看這些依賴到底是怎麼被注入的.

我們分析原始碼的不能一下子扎進原始碼堆裡不能自拔, 那麼分析原始碼該如何下手, 我覺得應該從使用它的地方入手. 比如Dagger2, 使用它的地方也就是觸發依賴注入的地方:

public class AddMenuBalanceFragment extends BaseFragment{
    @Inject
    AddMenuBalancePresenter presenter;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

    DaggerAddMenuBalanceComponent.builder()
        .menuBalanceRepoComponent(((CcdApplication) getActivity().getApplication()).getMenuBalanceRepoComponent())
        .addMenuBalancePresenterModule(new AddMenuBalancePresenterModule(this))
        .build()
        .inject(this); //完成注入
    }
}

從上面的程式碼可以直觀的看出DaggerAddMenuBalanceComponent使用了Builder模式, 設定了兩個引數 menuBalanceRepoComponent 和 addMenuBalancePresenterModule, 最後呼叫inject()把當前的Fragment作為引數傳遞進去了.

接下來看看inject()的實現 :

  @Override
  public void inject(AddMenuBalanceFragment fragment) {
    addMenuBalanceFragmentMembersInjector.injectMembers(fragment);
  }

然後看看DaggerAddMenuBalanceComponent中 addMenuBalanceFragmentMembersInjector是怎麼產生的:

  private void initialize(final Builder builder) {

    this.provideAddMenuBalanceViewProvider =
        AddMenuBalancePresenterModule_ProvideAddMenuBalanceViewFactory.create(
            builder.addMenuBalancePresenterModule);

    this.getMenuBalanceRepositoryProvider =
        new Factory<MenuBalanceRepository>() {
          private final MenuBalanceRepoComponent menuBalanceRepoComponent =
              builder.menuBalanceRepoComponent;

          @Override
          public MenuBalanceRepository get() {
            return Preconditions.checkNotNull(
                menuBalanceRepoComponent.getMenuBalanceRepository(),
                "Cannot return null from a [email protected] component method");
          }
        };

  this.addMenuBalancePresenterProvider =
          AddMenuBalancePresenter_Factory.create(
  provideAddMenuBalanceViewProvider, getMenuBalanceRepositoryProvider);

  this.addMenuBalanceFragmentMembersInjector =
          AddMenuBalanceFragment_MembersInjector.create(addMenuBalancePresenterProvider);
}

從initialize方法裡可以看出
addMenuBalanceFragmentMembersInjector依賴addMenuBalancePresenterProvider
addMenuBalancePresenterProvider又依賴provideAddMenuBalanceViewProvider和getMenuBalanceRepositoryProvider

所以要想明白addMenuBalanceFragmentMembersInjector是怎麼創建出來的, 就必須弄清楚addMenuBalancePresenterProvider,provideAddMenuBalanceViewProvider和getMenuBalanceRepositoryProvider.

1) provideAddMenuBalanceViewProvider屬性的分析

this.provideAddMenuBalanceViewProvider =
    AddMenuBalancePresenterModule_ProvideAddMenuBalanceViewFactory.create(
        builder.addMenuBalancePresenterModule);

從上面的程式碼可以看出, provideAddMenuBalanceViewProvider是通過AddMenuBalancePresenterModule_ProvideAddMenuBalanceViewFactory.create構建出來的：

  public static Factory<AddMenuBalanceContract.View> create(AddMenuBalancePresenterModule module) {
    return new AddMenuBalancePresenterModule_ProvideAddMenuBalanceViewFactory(module);
  }

然後看看構造方法和AddMenuBalancePresenterModule_ProvideAddMenuBalanceViewFactory.get()方法：

  public AddMenuBalancePresenterModule_ProvideAddMenuBalanceViewFactory(
      AddMenuBalancePresenterModule module) {
    assert module != null;
    this.module = module;
  }

  @Override
  public AddMenuBalanceContract.View get() {
    return Preconditions.checkNotNull(
        module.provideAddMenuBalanceView(),
        "Cannot return null from a [email protected] @Provides method");
  }

如此可見，AddMenuBalancePresenterModule_ProvideAddMenuBalanceViewFactory.get方法的返回值是通過傳遞進去的module.provideAddMenuBalanceView()提供的，這個module就是在Fragment中DaggerAddMenuBalanceComponent.build的時候設定進去的，程式碼如下：

public class AddMenuBalanceFragment extends BaseFragment{

    //ignore other code

    DaggerAddMenuBalanceComponent.builder()
        .addMenuBalancePresenterModule(new AddMenuBalancePresenterModule(this))
        .build()
        .inject(this); //完成注入
    }
}

說白了AddMenuBalancePresenterModule_ProvideAddMenuBalanceViewFactory的module就是AddMenuBalancePresenterModule(this). 這裡的this就是View了

看看AddMenuBalancePresenterModule的程式碼:

@Module
public class AddMenuBalancePresenterModule {

    private final AddMenuBalanceContract.View mView;

    public AddMenuBalancePresenterModule(AddMenuBalanceContract.View view) {
        mView = view;
    }

    @Provides
    AddMenuBalanceContract.View provideAddMenuBalanceView(){
        return mView;
    }
}

所以provideAddMenuBalanceViewProvider.get返回的值就是View也就是我們的Fragment了。

所以provideAddMenuBalanceViewProvider的作用就是返回View , 至此provideAddMenuBalanceViewProvider講解完畢了。

2) getMenuBalanceRepositoryProvider 屬性的分析

    this.getMenuBalanceRepositoryProvider =
        new Factory<MenuBalanceRepository>() {
          private final MenuBalanceRepoComponent menuBalanceRepoComponent =
              builder.menuBalanceRepoComponent;

          @Override
          public MenuBalanceRepository get() {
            return Preconditions.checkNotNull(
                menuBalanceRepoComponent.getMenuBalanceRepository(),
                "Cannot return null from a [email protected] component method");
          }
        };

從上面的程式碼可以看出, 它通過一個匿名內部類來實現的。先看看匿名內部類中的menuBalanceRepoComponent屬性

這裡的menuBalanceRepoComponent是build.menuBalanceRepoComponent，DaggerAddMenuBalanceComponent.build我們只在AddMenuBalanceFragment裡設定了引數了，如下：

DaggerAddMenuBalanceComponent.builder()
        .menuBalanceRepoComponent(((CcdApplication) getActivity().getApplication()).getMenuBalanceRepoComponent())
        .addMenuBalancePresenterModule(new AddMenuBalancePresenterModule(this))
        .build()
        .inject(this);

從程式碼可以看出menuBalanceRepoComponent就是((CcdApplication) getActivity().getApplication()).getMenuBalanceRepoComponent()

Ok, 那我們看看CcdApplication.getMenuBalanceRepoComponent() :

public void onCreate() {
    //...
    mMenuBalanceRepoComponent = DaggerMenuBalanceRepoComponent.builder()
            .applicationModule(new ApplicationModule(getApplicationContext()))
            .build();
}

public MenuBalanceRepoComponent getMenuBalanceRepoComponent() {
    return mMenuBalanceRepoComponent;
}

所以匿名內部類(Factory)中的getMenuBalanceRepositoryProvider屬性就是DaggerMenuBalanceRepoComponent.

然後再看匿名內部類(Factory)的get()方法, 返回的是 DaggerMenuBalanceRepoComponent.getMenuBalanceRepository();, getMenuBalanceRepository()方法具體是怎麼實現的:

public final class DaggerMenuBalanceRepoComponent implements MenuBalanceRepoComponent {
  @Override
  public MenuBalanceRepository getMenuBalanceRepository() {
    return menuBalanceRepositoryProvider.get();
  }
}

發現該方法返回的是menuBalanceRepositoryProvider.get(); , 那麼menuBalanceRepositoryProvider是什麼東西?

menuBalanceRepositoryProvider是在DaggerMenuBalanceRepoComponent.initialize(builder)中初始化：

  private void initialize(final Builder builder) {

    this.provideRemoteDataSourceProvider =
        ScopedProvider.create(
            MenuBalanceRepoModule_ProvideRemoteDataSourceFactory.create(
                builder.menuBalanceRepoModule));

    this.menuBalanceRepositoryProvider =
        ScopedProvider.create(
            MenuBalanceRepository_Factory.create(provideRemoteDataSourceProvider));
  }

從這段程式碼可以看出 menuBalanceRepositoryProvider初始化依賴於provideRemoteDataSourceProvider

所以又得先分析下 provideRemoteDataSourceProvider了, provideRemoteDataSourceProvider的初始化需要builder.menuBalanceRepoModule, 這個builder.menuBalanceRepoModule是在我們呼叫build的時候Dagger2建立的:

public MenuBalanceRepoComponent build() {
  if (menuBalanceRepoModule == null) {
    this.menuBalanceRepoModule = new MenuBalanceRepoModule();
  }
  return new DaggerMenuBalanceRepoComponent(this);
}

所以builder.menuBalanceRepoModule = new MenuBalanceRepoModule() , MenuBalanceRepoModule類的程式碼如下:

@Module
public class MenuBalanceRepoModule {

    @Singleton
    @Provides
    @Remote
    IMenuBalanceSource provideRemoteDataSource() {
        return new MenuBalanceRemoteSource();
    }
}

provideRemoteDataSourceProvider屬性需要MenuBalanceRepoModule_ProvideRemoteDataSourceFactory.create創建出來的, 那來看看這個工廠方法 :

  @Override
  public IMenuBalanceSource get() {
    return Preconditions.checkNotNull(
        module.provideRemoteDataSource(),
        "Cannot return null from a [email protected] @Provides method");
  }

  public static Factory<IMenuBalanceSource> create(MenuBalanceRepoModule module) {
    return new MenuBalanceRepoModule_ProvideRemoteDataSourceFactory(module);
  }

create方法的引數module就是我們剛剛分析的MenuBalanceRepoModule, 工廠方法的get方法返回的就是:

    IMenuBalanceSource provideRemoteDataSource() {
        return new MenuBalanceRemoteSource();
    }

所以provideRemoteDataSourceProvider的作用就是提供new MenuBalanceRemoteSource()物件的.

menuBalanceRepositoryProvider屬性依賴的引數provideRemoteDataSourceProvider講完了, 那麼就可以分析menuBalanceRepositoryProvider屬性了:

this.menuBalanceRepositoryProvider =
    ScopedProvider.create(
        MenuBalanceRepository_Factory.create(provideRemoteDataSourceProvider));

MenuBalanceRepository_Factory類:

  @Override
  public MenuBalanceRepository get() {
    return new MenuBalanceRepository(remoteSourceProvider.get());
  }

  public static Factory<MenuBalanceRepository> create(
      Provider<IMenuBalanceSource> remoteSourceProvider) {
    return new MenuBalanceRepository_Factory(remoteSourceProvider);
  }

它的get()方法new了一個MenuBalanceRepository, 構造這個MenuBalanceRepository需要MenuBalanceRemoteSource引數,通過傳進來的provideRemoteDataSourceProvider提供即可.

所以menuBalanceRepositoryProvider的作用就是提供new MenuBalanceRepository物件的.

所以DaggerMenuBalanceRepoComponent.getMenuBalanceRepository()方法返回的就是MenuBalanceRepository

  @Override
  public MenuBalanceRepository getMenuBalanceRepository() {
    return menuBalanceRepositoryProvider.get();
  }

再來回顧下匿名內部類(Factory) :

    this.getMenuBalanceRepositoryProvider =
        new Factory<MenuBalanceRepository>() {
          private final MenuBalanceRepoComponent menuBalanceRepoComponent =
              builder.menuBalanceRepoComponent;

          @Override
          public MenuBalanceRepository get() {
            return Preconditions.checkNotNull(
                menuBalanceRepoComponent.getMenuBalanceRepository(),
                "Cannot return null from a [email protected] component method");
          }
        };

到現在為止, 我們就可以解釋匿名內部類get()方法返回的是什麼了, 返回就是MenuBalanceRepository物件.

所以getMenuBalanceRepositoryProvider屬性的作用就是提供MenuBalanceRepository物件的.

3) addMenuBalancePresenterProvider 屬性的分析

addMenuBalancePresenterProvider屬性初始化所依賴的provideAddMenuBalanceViewProvider和getMenuBalanceRepositoryProvider都分析完畢了, 現在就可以分析addMenuBalancePresenterProvider屬性了.

通過上面的分析我們知道:

provideAddMenuBalanceViewProvider屬性的作用就是返回View

getMenuBalanceRepositoryProvider屬性的作用就是提供MenuBalanceRepository物件的

看看addMenuBalancePresenterProvider初始化程式碼如下:

  this.addMenuBalancePresenterProvider =
          AddMenuBalancePresenter_Factory.create(
  provideAddMenuBalanceViewProvider, getMenuBalanceRepositoryProvider);

AddMenuBalancePresenter_Factory類:

  public AddMenuBalancePresenter_Factory(
      Provider<AddMenuBalanceContract.View> viewProvider,
      Provider<MenuBalanceRepository> mMenuBalanceRepositoryProvider) {
    assert viewProvider != null;
    this.viewProvider = viewProvider;
    assert mMenuBalanceRepositoryProvider != null;
    this.mMenuBalanceRepositoryProvider = mMenuBalanceRepositoryProvider;
  }

  @Override
  public AddMenuBalancePresenter get() {
    return new AddMenuBalancePresenter(viewProvider.get(), mMenuBalanceRepositoryProvider.get());
  }

  public static Factory<AddMenuBalancePresenter> create(
      Provider<AddMenuBalanceContract.View> viewProvider,
      Provider<MenuBalanceRepository> mMenuBalanceRepositoryProvider) {
    return new AddMenuBalancePresenter_Factory(viewProvider, mMenuBalanceRepositoryProvider);
  }

通過它的get()方法就知道該工廠方法返回一個AddMenuBalancePresenter例項, 構造AddMenuBalancePresenter需要的兩個引數通過上面講解了兩個屬性provideAddMenuBalanceViewProvider和getMenuBalanceRepositoryProvider提供.

所以addMenuBalancePresenterProvider屬性的最終的作用就是提供AddMenuBalancePresenter物件的.

到此為止, 我們就知道了Presenter是怎麼被構建出來的了.

4) addMenuBalanceFragmentMembersInjector 屬性的分析

接下來分析DaggerAddMenuBalanceComponent最後一個需要分析的屬性addMenuBalanceFragmentMembersInjector

  this.addMenuBalanceFragmentMembersInjector =
          AddMenuBalanceFragment_MembersInjector.create(addMenuBalancePresenterProvider);

AddMenuBalanceFragment_MembersInjector類程式碼:

  public static MembersInjector<AddMenuBalanceFragment> create(
      Provider<AddMenuBalancePresenter> presenterProvider) {
    return new AddMenuBalanceFragment_MembersInjector(presenterProvider);
  }

  @Override
  public void injectMembers(AddMenuBalanceFragment instance) {
    if (instance == null) {
      throw new NullPointerException("Cannot inject members into a null reference");
    }
    instance.presenter = presenterProvider.get();
  }

核心就是injectMembers方法, 該方法完成了Fragment中對Presenter的注入, injectMembers方法所需要的引數 presenterProvider 就是addMenuBalancePresenterProvider屬性(提供AddMenuBalancePresenter物件的).

因為DaggerAddMenuBalanceComponent.inject()方法呼叫了AddMenuBalanceFragment_MembersInjector.injectMembers.

所以為什麼說呼叫DaggerAddMenuBalanceComponent.inject()方法就完成了依賴注入操作.

所以這也就是為什麼需要在Fragment中呼叫它了, 如下程式碼所示:

public class AddMenuBalanceFragment extends BaseFragment{
    @Inject
    AddMenuBalancePresenter presenter;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

    DaggerAddMenuBalanceComponent.builder()
        .menuBalanceRepoComponent(((CcdApplication) getActivity().getApplication()).getMenuBalanceRepoComponent())
        .addMenuBalancePresenterModule(new AddMenuBalancePresenterModule(this))
        .build()
        .inject(this); //完成注入
    }
}

上面的原始碼分析流程可以用如下圖來表示 :

Dagger2生成類我們寫的Component和Module類對應關係

AddMenuBalanceComponent(Interface) –> DaggerAddMenuBalanceComponent implements AddMenuBalanceComponent

AddMenuBalancePresenterModule –> AddMenuBalancePresenterModule_ProvideAddMenuBalanceViewFactory

MenuBalanceRepoComponent(Interface) –> DaggerMenuBalanceRepoComponent implements MenuBalanceRepoComponent

MenuBalanceRepoModule –> MenuBalanceRepoModule_ProvideRemoteDataSourceFactory

從上面的原始碼分析，Dagger2生成的原始碼大量使用了Builder、Factory模式。