RecyclerView with different ViewHolder using generic

Question

I have different ViewHolder for different Feed implementations. But I can't use the best practice of having each ViewHolder corresponds to different layout id because i am reusing layout for 2 different ViewHolder (aka. FeedWithImageHolder and FeedWithoutImageHolder)

class FeedAdapter extends RecyclerView.Adapter<FeedAdapter.BaseFeedHolder>{

    @NonNull
    @Override
    public BaseFeedHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View v = null;
        switch (viewType){
            case FeedType.FEED_WITH_IMAGE :
                v = LayoutInflater.from(context).inflate(R.layout.feed_status,parent,false);
                //notice that i use the same R.layout.feed_status for two different ViewHolder

                return new FeedWithImageHolder(v);
            case FeedType.FEED_WITHOUT_IMAGE:
                v = LayoutInflater.from(context).inflate(R.layout.feed_status,parent,false);
                return new FeedWithoutImageHolder(v);
            case FeedType.ADS:
                v = LayoutInflater.from(context).inflate(R.layout.ads,parent,false);
                return new AdsHolder(v);
        }
        return null;
    }

    @Override
    public void onBindViewHolder(@NonNull BaseFeedHolder holder, int position) {
        //noinspection unchecked
        holder.bindFeed(feeds.get(position));
    }

    abstract class BaseFeedHolder<T extends Feed> extends RecyclerView.ViewHolder {
        BaseFeedHolder(@NonNull View itemView) {
            super(itemView);
        }

        abstract void bindFeed(T feed);
    }

    class FeedWithImageHolder extends BaseFeedHolder<FeedStatus>{

        FeedWithImageHolder(@NonNull View itemView) {
            super(itemView);
        }

        @Override
        void bindFeed(FeedStatus feed) {
            doSomethingWithFeed(feed);
            bindImage(feed.getPostImage());
        }

        protected void bindImage(String image){
            clipImageToImageView(image);
        }
    }

    class FeedWithoutImageHolder extends FeedWithImageHolder{

        FeedWithoutImageHolder(@NonNull View itemView) {
            super(itemView);
            removeImageViewFromCoinstraintLayout(itemView);
        }

        @Override
        protected void bindImage(String image) {
            //void
        }
    }

    class AdsHolder extends BaseFeedHolder<Ads>{
        AdsHolder(@NonNull View itemView) {
            super(itemView);
        }

        @Override
        void bindFeed(Ads ads) {
        }
    }

}

Instead what I do is making Feed have a method .getType() so every implementation can have different type corresponding to it.

For example:

class FeedStatus implements Feed { 

    private String image;

    @Override
    public int getType() {
        return (this.image == null) ? FeedType.FEED_WITHOUT_IMAGE : FeedType.FEED_WITH_IMAGE;
    }

}

There is tingling worry here because I think there is code smell in there but I am not sure which one and I hope you can help me with it. Thanks

Answer 1

From a quick glance, I share your concerns.

One 'smell' is that a sub-class (FeedWithoutImageHolder) provides less functionality than the parent class, i.e. it does not actually "extend" the class.

I suggest trying to align layout structure and functionality:

Create two different layouts: The first one without an image, and a second one which includes the first and extends it by adding an image. Depending on your desired layout design, you may instead want to declare only one layout which includes some empty placeholder element of the desired image display size which either stays empty or receives an image, so that all visual elements align.

I recommend against having a Feed handle the type of layout at all. Keep data objects and layout concerns separate, that's what the Adapter is for. Have the adapter check if an image needs to be displayed for an item and determine the appropriate view type in Adapter.getItemViewType().