getSupportFragmentManager（）上的NullPointerException

Question

我正在线上NullPointerException：

FragmentManager fragmentManager = ((ProductActivity)context).getSupportFragmentManager();
fragmentManager.beginTransaction().replace(R.id.frame_container, fragment).commit();

上下文返回null，当我点击替换下面适配器中的片段时，它就崩溃了。

这是我的适配器：

public class ProductActivityAdapter extends RecyclerView.Adapter<ProductActivityAdapter.ViewHolder> {

        private List<Product> products;
        private int rowLayout;
        public Context mContext;
        public  int position;

        public ProductActivityAdapter(List<Product> products, int rowLayout, Context context) {
        this.products = products;
        this.rowLayout = rowLayout;
        this.mContext = context;
            }

        @Override
            public ViewHolder onCreateViewHolder(ViewGroup viewGroup, int i) {
                View v = LayoutInflater.from(viewGroup.getContext()).inflate(rowLayout, viewGroup, false);
        return new ViewHolder(v);
            }


        @Override
            public void onBindViewHolder(ViewHolder viewHolder, int i) {
                Product product = products.get(i);
                viewHolder.card.setTag(i);
                viewHolder.countryName.setText(product.name);
        if(android.os.Build.VERSION.SDK_INT >= 21){
        //  viewHolder.countryImage.setImageDrawable(mContext.getDrawable(product.getImageResourceId(mContext)));
                    viewHolder.iconImage.setImageDrawable(mContext.getDrawable(product.getIconImage(mContext)));
                } else {
        //  viewHolder.countryImage.setImageDrawable(mContext.getResources().getDrawable(product.getImageResourceId(mContext)));
                    viewHolder.iconImage.setImageDrawable(mContext.getResources().getDrawable(product.getIconImage(mContext)));


                }

            }

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

        public static class ViewHolder extends RecyclerView.ViewHolder  {
        public TextView countryName;
        public ImageView countryImage;
        public ImageView iconImage;
        public CardView card;
        public Context context;

        public Context getContext() {
        return context;
                    }
            public ViewHolder(View itemView) {
        super(itemView);
        countryName = (TextView) itemView.findViewById(R.id.countryName);
        // countryImage = (ImageView)itemView.findViewById(R.id.countryImage);
                    iconImage = (ImageView) itemView.findViewById(R.id.iconImage);
        card = (CardView) itemView.findViewById(R.id.card);
        card.setOnClickListener(new CardClickListener());

                }
        private class CardClickListener implements CardView.OnClickListener {

        @Override
                        public void onClick(View v) {
        //  Log.e("VIEW", "position=" + position);
                            int position = (int) v.getTag();
                            Log.e("VIEW", "position=" + position);
                            cardview(position);

                        }
                    }

        public void cardview(int position) {
                    Fragment fragment = null;
        switch (position) {
        case 0:
                            fragment = new emi_calculator_fragment();
        break;
        case 1:
                            Log.e("Position", "HI");
        break;
        case 2:
                            Log.e("Position", "HI");
        break;
        case 3:
                            Log.e("Position", "HI");
        break;
        case 4:
                            Log.e("Position", "HI");
        break;
        case 5:
                            Log.e("Position", "HI");
        break;

        default:
        break;
                    }
        if (fragment != null) {

                        FragmentManager fragmentManager = ((ProductActivity)context).getSupportFragmentManager();
                        fragmentManager.beginTransaction()
                                .replace(R.id.frame_container, fragment).commit();

                    } else {
        // error in creating fragment
                        Log.e("Product Activity", "Error in creating fragment");
                    }
                }   
            }
            }

Answer 1

使用

mContext.getSupportFragmentManager();

而不是

((ProductActivity)context).getSupportFragmentManager();

您已将Context定义为mContext。

Answer 2

在ViewHolder类中，您没有设置上下文，因此它为null。

public ViewHolder(Context context, View itemView) {
  super(itemView);
  this.context = context;
  ...
}