java - 通过删除清除所有项目后列表返回一项

Question

我的列表在通过删除清除所有项目后返回一个项目，在应用程序全新安装时返回 null，这很好，但在添加项目然后删除所有项目后，从该 Activity 返回并再次出现时会发生这种情况，列表.size() 返回 1 并且有一个项目保留，我不知道它是否从缓存对象实例加载，这是我的适配器类代码

[请查看所附图片，列表为空，但计数器仍然为 1 counter = cartModelList.size()]我有一个购物车项目列表 private List<CartModel> cartModelList;

它正在返回null在应用程序全新安装上，这很好，但是当我将商品添加到购物车然后删除所有商品时，它会返回 1。

我的意思是cartmodelList.size()据我所知，它正在返回缓存对象中的一些项目或类似的东西。

The question is how to remove that List object cached or any alternative?

我尝试了删除按钮，但仍然缓存了

    public static  double p = 0;
    private List<CartModel> cartModelList;
    Database db;
    Context context;

    public CartAdapter(Context context, List<CartModel> cartModelList) {
        this.cartModelList = cartModelList;
        this.context = context;
        db = new Database(context);
    }

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

    @Override
    public void onBindViewHolder(@NonNull final Viewholder holder, final int position) {


        String namee = cartModelList.get(position).getName();
        String manufacturere = cartModelList.get(position).getManufacturer();
        String availabilitye = cartModelList.get(position).getAvailability();
        String e_parte = cartModelList.get(position).getE_part();
        String m_parte = cartModelList.get(position).getM_part();
        String floatprice = cartModelList.get(position).getUnit_();
        String int_quantity = cartModelList.get(position).getQuantity();
        String float_line_total = cartModelList.get(position).getLine_total();



        holder.setItemDetails(namee, manufacturere, availabilitye, e_parte, m_parte, floatprice, int_quantity, float_line_total);


        int  checker = SharedPrefManager.getInstance(context).cartcount().getCounter();

        if (checker <= 0){

            cartModelList.clear();

        }

        holder.btn_delete.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                if (db.deleteProduct(cartModelList.get(position).getID())) {

                        cartModelList.remove(position);
                        notifyDataSetChanged();

                    Toast.makeText(context, "Product  deleted from cart", Toast.LENGTH_LONG).show();



                } else {

                    Toast.makeText(context, "Product not deleted from cart", Toast.LENGTH_LONG).show();

                }

                CartList user111 = new CartList(--COUNTER_BADGE);

                //  Toast.makeText(context, "else", Toast.LENGTH_SHORT).show();
                SharedPrefManager.getInstance(context).cartList(user111);
                ((Activity)context).invalidateOptionsMenu();
                ((Activity)context).finish();
                Intent intent = new Intent(context, CartActivity.class);
                intent.addFlags(Intent.FLAG_ACTIVITY_NO_ANIMATION);
                context.startActivity(intent);

            }



        });


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

    class Viewholder extends RecyclerView.ViewHolder {

        private TextView name;
        private TextView manufacturer;
        private TextView availability;
        private TextView e_part;
        private TextView m_part;
        private TextView price;
        private EditText quantity;
        private TextView linetotal;
        private Button btn_delete;
        private Button btn_update;
        private  Button adapter_livestock;
        public  SpinKitView progressbar;

        public Viewholder(@NonNull View itemView) {
            super(itemView);

            name = itemView.findViewById(R.id.name);
            manufacturer = itemView.findViewById(R.id.manufacturer);
            availability = itemView.findViewById(R.id.availability);
            e_part = itemView.findViewById(R.id.e_part);
            m_part = itemView.findViewById(R.id.m_part);
            price = itemView.findViewById(R.id.price);
            quantity = itemView.findViewById(R.id.quantity);
            linetotal = itemView.findViewById(R.id.linetotal);
            btn_delete = itemView.findViewById(R.id.btn_delete);
            btn_update = itemView.findViewById(R.id.btn_update);
            adapter_livestock = itemView.findViewById(R.id.adapter_livestock);
            progressbar = itemView.findViewById(R.id.adapterrprogresslivestockprogress);

        }


        private void setItemDetails(String namee, String manufacturere, String availabilitye, String e_parte, String m_parte, String floatprice, String int_quantity, String float_line_total) {

            name.setText(namee);
            manufacturer.setText(manufacturere);
            availability.setText(availabilitye);
            e_part.setText(e_parte);
            m_part.setText(m_parte);
            price.setText("£"+floatprice);
            quantity.setText(int_quantity);
            linetotal.setText("£"+float_line_total);


        }


    }

[/image/PxDTZ.jpg]

Answer 1

好的...第一个。

if (db.deleteProduct(cartModelList.get(position).getID())) 

不会从 cartModelList 中删除您的商品，您需要手动执行此操作。像这样:

if (db.deleteProduct(cartModelList.get(position).getID())) {
    cartModelList.remove(position)

还有第二个。您必须仅在删除方法的末尾调用notifyDataSetChanged()或itemChanged或itemRemoved等。请告诉我它是否有效。

附注您的项目不会被缓存。问题出在您的代码顺序中。

编辑 1. 另外，您需要检查您的 db.deleteProduct 方法。有效吗？你的 if 语句有效吗？

编辑2。试试这个。

holder.btn_delete.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            if (db.deleteProduct(cartModelList.get(position).getID())) {
                    cartModelList.remove(position);
                    notifyItemRemoved(position);

                Toast.makeText(context, "Product  deleted from cart", Toast.LENGTH_LONG).show();
            } else {
                Toast.makeText(context, "Product not deleted from cart", Toast.LENGTH_LONG).show();
            }

            CartList user111 = new CartList(cartModelList.size());

            //  Toast.makeText(context, "else", Toast.LENGTH_SHORT).show();
            SharedPrefManager.getInstance(context).cartList(user111);
            ((Activity)context).invalidateOptionsMenu();
            ((Activity)context).finish();
            Intent intent = new Intent(context, CartActivity.class);
            intent.addFlags(Intent.FLAG_ACTIVITY_NO_ANIMATION);
            context.startActivity(intent);
        }
    });