如何使用 dagger2 将 Activity 注入适配器

Question

Android Studio 3.0 金丝雀 8

我正在尝试将我的 MainActivity 注入我的 Adapter。然而，我的解决方案工作正常，但我认为它有代码味道而不是正确的方法。

我的适配器代码段看起来像这样，但我不喜欢的是我必须将 Activity 转换为 MainActivity:

public class RecipeAdapter extends RecyclerView.Adapter<RecipeListViewHolder> {
    private List<Recipe> recipeList = Collections.emptyList();
    private Map<Integer, RecipeListViewHolderFactory> viewHolderFactories;
    private MainActivity mainActivity;

    public RecipeAdapter(Activity activity, Map<Integer, RecipeListViewHolderFactory> viewHolderFactories) {
        this.recipeList = new ArrayList<>();
        this.viewHolderFactories = viewHolderFactories;
        this.mainActivity = (MainActivity)activity;
    }

    @Override
    public RecipeListViewHolder onCreateViewHolder(ViewGroup viewGroup, int i) {
        /* Inject the viewholder */
        final RecipeListViewHolder recipeListViewHolder = viewHolderFactories.get(Constants.RECIPE_LIST).createViewHolder(viewGroup);

        recipeListViewHolder.itemView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                /* Using the MainActivity to call a callback listener */
                mainActivity.onRecipeItemClick(getRecipe(recipeListViewHolder.getAdapterPosition()));
            }
        });

        return recipeListViewHolder;
    }
}

在我的模块中，我在模块的构造函数中传递 Activity 并将其传递给适配器。

@Module
public class RecipeListModule {
    private Activity activity;

    public RecipeListModule() {}

    public RecipeListModule(Activity activity) {
        this.activity = activity;
    }

    @RecipeListScope
    @Provides
    RecipeAdapter providesRecipeAdapter(Map<Integer, RecipeListViewHolderFactory> viewHolderFactories) {
        return new RecipeAdapter(activity, viewHolderFactories);
    }
}

在我的应用程序中 class 我创建了组件并为适配器使用了 SubComponent。在这里，我必须通过 Activity，我不确定这是个好主意。

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

    applicationComponent = createApplicationComponent();
    recipeListComponent = createRecipeListComponent();
}

public BusbyBakingComponent createApplicationComponent() {
    return DaggerBusbyBakingComponent.builder()
            .networkModule(new NetworkModule())
            .androidModule(new AndroidModule(BusbyBakingApplication.this))
            .exoPlayerModule(new ExoPlayerModule())
            .build();
}

public RecipeListComponent createRecipeListComponent(Activity activity) {
    return recipeListComponent = applicationComponent.add(new RecipeListModule(activity));
}

我的片段是这样注入的：

@Inject RecipeAdapter recipeAdapter;

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

        ((BusbyBakingApplication)getActivity().getApplication())
                .createRecipeListComponent(getActivity())
                .inject(this);
    }

尽管上述设计有效，但我认为这是一种代码味道，因为我必须将 Activity 转换为 MainActivity。我使用 Activity 的原因是我想让这个模块更通用。

只是想知道有没有更好的方法

=============== 使用界面更新

界面

public interface RecipeItemClickListener {
    void onRecipeItemClick(Recipe recipe);
}

实施

public class RecipeItemClickListenerImp implements RecipeItemClickListener {
    @Override
    public void onRecipeItemClick(Recipe recipe, Context context) {
        final Intent intent = Henson.with(context)
                .gotoRecipeDetailActivity()
                .recipe(recipe)
                .build();

        context.startActivity(intent);
    }
}

在我的模块中，我有以下供应商

@Module
public class RecipeListModule {
    @RecipeListScope
    @Provides
    RecipeItemClickListener providesRecipeItemClickListenerImp() {
        return new RecipeItemClickListenerImp();
    }

    @RecipeListScope
    @Provides
    RecipeAdapter providesRecipeAdapter(RecipeItemClickListener recipeItemClickListener, Map<Integer, RecipeListViewHolderFactory> viewHolderFactories) {
        return new RecipeAdapter(recipeItemClickListener, viewHolderFactories);
    }
}

然后我通过 RecipeAdapter 中的构造函数注入使用它

public class RecipeAdapter extends RecyclerView.Adapter<RecipeListViewHolder> {
    private List<Recipe> recipeList = Collections.emptyList();
    private Map<Integer, RecipeListViewHolderFactory> viewHolderFactories;
    private RecipeItemClickListener recipeItemClickListener;

    @Inject /* IS THIS NESSESSARY - AS IT WORKS WITH AND WITHOUT THE @Inject annotation */
    public RecipeAdapter(RecipeItemClickListener recipeItemClickListener, Map<Integer, RecipeListViewHolderFactory> viewHolderFactories) {
        this.recipeList = new ArrayList<>();
        this.viewHolderFactories = viewHolderFactories;
        this.recipeItemClickListener = recipeItemClickListener;
    }

    @Override
    public RecipeListViewHolder onCreateViewHolder(final ViewGroup viewGroup, int i) {
        /* Inject the viewholder */
        final RecipeListViewHolder recipeListViewHolder = viewHolderFactories.get(Constants.RECIPE_LIST).createViewHolder(viewGroup);

        recipeListViewHolder.itemView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                recipeItemClickListener.onRecipeItemClick(getRecipe(recipeListViewHolder.getAdapterPosition()), viewGroup.getContext());
            }
        });

        return recipeListViewHolder;
    }
}

只有一个问题，RecipeAdapter 中的构造函数需要@Inject 注释。无论是否使用 @Inject.

Answer 1

不要将 Activity 传递给适配器 - 这是一个非常糟糕的做法。

只注入您关心的字段。

在您的示例中：将接口传递到适配器以跟踪项目点击。

Answer 2

如果您需要 MainActivity，那么您也应该提供。而不是 Activity 为您的模块声明 MainActivity。

@Module
public class RecipeListModule {
  private MainActivity activity;

  public RecipeListModule(MainActivity activity) {
    this.activity = activity;
  }
}

并且您的适配器应该只请求它（非 Android 框架类型的构造函数注入！）

@RecipeListScope
class RecipeAdapter {

  @Inject
  RecipeAdapter(MainActivity activity,
          Map<Integer, RecipeListViewHolderFactory> viewHolderFactories) {
    // ...
  }

}

如果您希望您的模块使用 Activity 而不是 MainActivity，那么您将需要声明一个已经提到的接口。然后，您的适配器会将接口声明为它的依赖项。

但在某些模块中，您仍然需要将该接口绑定到您的 MainActivity，并且一个模块需要知道如何提供依赖项。

// in some abstract module
@Binds MyAdapterInterface(MainActivity activity) // bind the activity to the interface

解决问题的更新部分

Just one question, is the @Inject annotation need for the constructor in the RecipeAdapter. As it works with or without the @Inject.

没有它也能工作，因为你还没有使用构造函数注入。您仍然在 providesRecipeAdapter() 中调用构造函数 您自己 。作为一般经验法则——如果你想正确使用 Dagger——永远不要自己调用 new。如果您想使用 new 问问自己是否可以改用构造函数注入。

您展示的同一模块可以如下编写，利用 @Binds 将实现绑定到接口，并实际使用构造函数注入来创建适配器（这就是为什么我们没有为它编写任何方法！维护的代码更少，错误更少，可读性更高类)

如您所见，我不需要自己使用 new — Dagger 会为我创建对象。

public abstract class RecipeListModule {
  @RecipeListScope
  @Binds
  RecipeItemClickListener providesRecipeClickListener(RecipeItemClickListenerImp listener);
}

Answer 3

就我个人而言，我会使用以下技巧

public class MainActivity extends AppCompatActivity {
    private static final String TAG = "__ACTIVITY__";

    public static MainActivity get(Context context) {
        // noinspection ResourceType
        return (MainActivity)context.getSystemService(TAG);
    }

    @Override
    protected Object getSystemService(String name) {
        if(TAG.equals(name)) {
            return this;
        }
        return super.getSystemService(name);
    }
}

public class RecipeAdapter extends RecyclerView.Adapter<RecipeListViewHolder> {
    private List<Recipe> recipeList = Collections.emptyList();
    private Map<Integer, RecipeListViewHolderFactory> viewHolderFactories;

    public RecipeAdapter(Map<Integer, RecipeListViewHolderFactory> viewHolderFactories) {
        this.recipeList = new ArrayList<>();
        this.viewHolderFactories = viewHolderFactories;
    }

    @Override
    public RecipeListViewHolder onCreateViewHolder(ViewGroup viewGroup, int i) {
        /* Inject the viewholder */
        final RecipeListViewHolder recipeListViewHolder = viewHolderFactories.get(Constants.RECIPE_LIST).createViewHolder(viewGroup);

        recipeListViewHolder.itemView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                MainActivity mainActivity = MainActivity.get(v.getContext());
                if(recipeListViewHolder.getAdapterPosition() != -1) {
                    mainActivity.onRecipeItemClick(
                      getRecipe(recipeListViewHolder.getAdapterPosition()));
                }
            }
        });

        return recipeListViewHolder;
    }
}

如何使用 dagger2 将 Activity 注入适配器

How to inject an Activity into an Adapter using dagger2

android

dagger-2