java - RecyclerAdapter getItemCount 崩溃

Question

我遇到以下问题，不幸的是，我的应用程序在进入下一个 Activity 时停止了。罪魁祸首是:

   public class RecyclerAdapter extends RecyclerView.Adapter<RecyclerAdapter.RecyclerHolder> {

        ArrayList<Theme> themes;
        private LayoutInflater mInflater;

       public RecyclerAdapter(Context context, ArrayList<Theme> themes) {
            mInflater = LayoutInflater.from(context);
            this.themes = themes;
       }

        public class RecyclerHolder extends RecyclerView.ViewHolder {

            ImageView imageView;
            TextView name,price;

            public RecyclerHolder(View view) {
                super(view);
                imageView = (ImageView)view.findViewById(R.id.demo);
                name = (TextView)view.findViewById(R.id.name);
                price = (TextView)view.findViewById(R.id.price);
            }
        }

        @NonNull
        @Override
        public RecyclerHolder onCreateViewHolder(@NonNull ViewGroup viewGroup, int i) {
            View view = mInflater.inflate(R.layout.recycler_list, viewGroup, false);
            return new RecyclerHolder(view);
        }

        @Override
        public void onBindViewHolder(@NonNull RecyclerHolder viewHolder, int i) {
           Log.i("log", themes.get(i).getName());
           viewHolder.imageView.setImageResource(themes.get(i).getDrawableCover());
           viewHolder.name.setText(themes.get(i).getName());
           viewHolder.price.setText(themes.get(i).getPrice());
        }

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

问题似乎出在 getItemCount() 方法上。当我尝试返回themes.size()时，应用程序崩溃了。当我 return 0 时，什么也没有显示。这里似乎有什么问题？我是android新手，所以请正确解释。

Answer 1

您想在 getItemCount() 方法中检查数据是否为 ​​null，这样您就可以确保您的应用永远不会崩溃:

Java:

@Override
public int getItemCount() {
   return themes != null ? themes.size() : 0;
}

Kotlin :

override fun getItemCount(): Int = themes?.size ?: 0