Is there a way to use a ViewStub inside a RecyclerView?

问题

i'm new to android, I've been working on a project, and in my news feeds page, I'm trying to include a modular feed RecyclerView, which shows a question with different answer forms, varrying according to the Question type. The way I was doing it so far was by using the include and turning the forms visible when needed. recently since i added more modules, the app started to slowdown segnificantly, so i'm trying to implement ViewStubs.

This is my RecyclerView adapter:

public class ReQuestionAdapter extends RecyclerView.Adapter<FeedItem> {
private ArrayList<Question> myQuestions;
public ReQuestionAdapter(Context context, ArrayList<Question> questions) {
    myQuestions = questions ;
}

@Override
public FeedItem onCreateViewHolder(ViewGroup parent, int viewType) {
    View view = LayoutInflater.from(parent.getContext())
            .inflate(R.layout.list_item_re_question, parent, false);
    return new FeedItem(view);
}

@Override
public void onBindViewHolder(FeedItem holder, int position) {
    Question q = myQuestions.get(position);
    holder.bindQuestion(q);
}

@Override
public int getItemViewType(int position) {
    return 0;
}

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

And this is the ViewHolder class for the adapter:

public class FeedItem extends RecyclerView.ViewHolder{
private Question mQuestion;
public TextView tvName;
public TextView tvTime;
public TextView tvContent;
public ProfilePictureView profilePictureView;
public ViewStub moduleView;
private int moduleType;

public FeedItem(View itemView) {
    super(itemView);

}

public void bindQuestion(Question question) {
    mQuestion = question;
    tvTime = (TextView) itemView.findViewById(R.id.li_q_date);
    tvContent = (TextView) itemView.findViewById(R.id.li_q_content);
    moduleView = (ViewStub) itemView.findViewById(R.id.module_viewstub);
    tvTime.setText(TimeHandler.When(mQuestion.publish_time));
    tvContent.setText(mQuestion.content);
    moduleType = question.type;
        switch (moduleType) {
            case Question.TYPE_YN:
                moduleView.setLayoutResource(R.layout.module_yes_no);
                moduleView.inflate();
                break;
            case Question.TYPE_CUSTOM:
                moduleView.setLayoutResource(R.layout.module_custom);
                moduleView.inflate();
                break;
            default:
                break;
        }
    }
}

Now, the problem is that the ViewStub which contains a certain layout, cannot be reinflated with a new one, the reason for that is that it gets removed from the view hirarchy as soon as it leaves the screen, the symptoms: When scrolling down the RecyclerView, the first list items that fill the screen are working perfect, but others to load when the previous leave the screen cause the FeedItem binding to bring a NullPointerException. (It canno't find it in the list item layout).

I'm looking for a solution as efficiant as ViewStubs, or a way to make them work properly, since I got many modules and inflating them all in each item as invisible would make my app slow.

回答1:

In your bindQuestion() method you are referencing two different layouts to inflate, so in essence you have two different view types.

Adapter views have an efficient way way to handle this built right in.

Start by overriding getItemViewType(). When the item at position gets the module_yes_no layout, return 0. When it gets the module_custom layout, return 1.

Then in onCreateViewHolder(), when the viewType parameter is 0, inflate a list_item_re_question view complete with the module_yes_no layout. When viewType == 1, inflate the module_custom version of the view.

Now when you get a view in onBindViewHolder(), it will already have the correct subview, so you proceed to fill out that view as needed. By using getItemViewType(), the RecyclerView is working with you to recycle the exact view you need.

You can even have two FeedItem subclasses, one for module_yes_no and one for module_custom, so in onBindViewHolder(), you just check the class of the ViewHolder and branch accordingly.

That should help improve the performance of your app.

来源：https://stackoverflow.com/questions/31609215/is-there-a-way-to-use-a-viewstub-inside-a-recyclerview