Android Architecture Components: using ViewModel for RecyclerView items

Question

I'm experimenting with the Architecture Components, and I want to build a ViewModel for each item of a RecyclerView. I'm not sure if that is formally correct or I should stick with the "old way".

I have this adapter:

public class PostAdapter extends RecyclerView.Adapter<PostAdapter.PostViewHolder> {      private List<Post> list;     public static class PostViewHolder extends RecyclerView.ViewHolder{         final ItemPostBinding binding;          public PostViewHolder(ItemPostBinding binding){             super(binding.getRoot());             this.binding = binding;         }     }      @Override     public PostViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {         ItemPostBinding binding = DataBindingUtil                 .inflate(LayoutInflater.from(parent.getContext()), R.layout.item_post,                         parent, false);           return new PostViewHolder(binding, parent.getContext());     }      @Override     public void onBindViewHolder(PostViewHolder holder, int position) {         holder.binding.setPost(list.get(position));         holder.binding.executePendingBindings();     }      @Override     public int getItemCount() {         return list == null ? 0 : list.size();     }      public void setList(List<Post> list){         this.list = list;         notifyDataSetChanged();     } } 

which works fine but it's very basic. how do I update it so each item has it's own ViewModel associated? is that even possible?

EDIT: playing with it, I've tried to put in ViewModels the following way:

public class PostAdapter extends RecyclerView.Adapter<PostAdapter.PostViewHolder> {      private List<Post> list;     public static class PostViewHolder extends RecyclerView.ViewHolder{         final ItemPostBinding binding;         private final Context context;         private GalleryItemViewModel viewModel;          public PostViewHolder(ItemPostBinding binding, Context context){             super(binding.getRoot());             this.binding = binding;             this.context = context;         }          public Context getContext(){             return context;         }          public void setViewModel(GalleryItemViewModel viewModel){             this.viewModel = viewModel;             binding.setViewModel(viewModel);         }     }      @Override     public PostViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {         ItemPostBinding binding = DataBindingUtil                 .inflate(LayoutInflater.from(parent.getContext()), R.layout.item_post,                         parent, false);           return new PostViewHolder(binding, parent.getContext());     }      @Override     public void onBindViewHolder(PostViewHolder holder, int position) {         GalleryItemViewModel vm = ViewModelProviders.of((FragmentActivity) holder.getContext()).get(GalleryItemViewModel.class);         vm.setPost(list.get(position));         holder.setViewModel(vm);     }      @Override     public int getItemCount() {         return list == null ? 0 : list.size();     }      public void setList(List<Post> list){         this.list = list;         notifyDataSetChanged();     } } 

it works but is that the correct way to do it?

Answer 1

Funny, but answer - This is correct way, should be accepted :) You can make some code clean-up and remove GalleryItemViewModel from PostViewHolder, because you are creating hard reference and not using it. Then dirrectly in onBindViewHolder() use it like holder.binding.setViewModel(vm);

This is a link with MVVM code example that can help you.