AdapterDelegates

Read the motivation for this project in my blog post.

Idea

The idea of this library is to build your adapters by composing reusable components.

Favor composition over inheritance

The idea is that you define an AdapterDelegate for each view type. This delegate is responsible for creating ViewHolder and binding ViewHolder for a certain viewtype. An AdapterDelegate get added to an AdapterDelegatesManager. This manager is the man in the middle between RecyclerView.Adapter and each AdapterDelegate.

For example:

public class CatAdapterDelegate extends AbsAdapterDelegate<List<Animal>> {

  private LayoutInflater inflater;

  public CatAdapterDelegate(Activity activity, int viewType) {
    super(viewType);
    inflater = activity.getLayoutInflater();
  }

  @Override public boolean isForViewType(@NonNull List<Animal> items, int position) {
    return items.get(position) instanceof Cat;
  }

  @NonNull @Override public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent) {
    return new CatViewHolder(inflater.inflate(R.layout.item_cat, parent, false));
  }

  @Override public void onBindViewHolder(@NonNull List<Animal> items, int position,
      @NonNull RecyclerView.ViewHolder holder) {

    CatViewHolder vh = (CatViewHolder) holder;
    Cat cat = (Cat) items.get(position);

    vh.name.setText(cat.getName());
  }

  static class CatViewHolder extends RecyclerView.ViewHolder {

    public TextView name;

    public CatViewHolder(View itemView) {
      super(itemView);
      name = (TextView) itemView.findViewById(R.id.name);
    }
  }
}

Then an AnimalAdapter could look like this:

public class AnimalAdapter extends RecyclerView.Adapter {

  private AdapterDelegatesManager<List<Animal>> delegatesManager;
  private List<Animal> items;

  public MainAdapter(Activity activity, List<Animal> items) {
    this.items = items;

    // Delegates
    delegatesManager = new AdapterDelegatesManager<>();
    delegatesManager.addDelegate(new CatAdapterDelegate(activity, 0));
    delegatesManager.addDelegate(new DogAdapterDelegate(activity, 1));
    delegatesManager.addDelegate(new GeckoAdapterDelegate(activity, 2));
    delegatesManager.addDelegate(new SnakeAdapterDelegate(activity, 3));

  }

  @Override public int getItemViewType(int position) {
    return delegatesManager.getItemViewType(items, position);
  }

  @Override public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
    return delegatesManager.onCreateViewHolder(parent, viewType);
  }

  @Override public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
    delegatesManager.onBindViewHolder(items, position, holder);
  }

  @Override public int getItemCount() {
    return items.size();
  }
}

Reducing boilerplate code

As you have seen in the code snipped above this may require to write the same boiler plate code again and again to hook in AdapterDelegatesManager to Adapter. This can be reduced by extending either from ListDelegationAdapter if the data source the adapter displays is java.util.List<?> or AbsDelegationAdapter which is a more general one (not limited to java.util.List)

In example the same AnimalAdapter from above could be simplified as follows by exending from ListDelegationAdapter:

public class AnimalAdapter extends ListDelegationAdapter<List<Animal>> {

  public AnimalAdapter(Activity activity, List<Animal> items) {

    // DelegatesManager is a protected Field in ListDelegationAdapter
    delegatesManager.addDelegate(new CatAdapterDelegate(activity, 0));
    delegatesManager.addDelegate(new DogAdapterDelegate(activity, 1));
    delegatesManager.addDelegate(new GeckoAdapterDelegate(activity, 2));
    delegatesManager.addDelegate(new SnakeAdapterDelegate(activity, 3));

    // Set the items from super class.
    setItems(items);
  }
}

Dependencies

This library is available on maven central:

compile 'com.hannesdorfmann:adapterdelegates:1.0.2'

hanhailong / adapterdelegates Goto Github PK