Question

我需要在“小计”中显示我的购物车活动中所有商品价格的总计我仍然收到错误消息：

java.lang.NullPointerException：尝试调用虚拟方法空对象引用上的“ void android.widget.TextView.setText（double）”

我认为这是因为小计声明是错误的，但是我不知道为什么。

我的代码：

DROP TABLE IF EXISTS t;
CREATE TABLE t( id integer,f integer, x integer);

INSERT INTO t VALUES (1,1,2), (1,2,4), (1,3,5);
INSERT INTO t VALUES (2,1,10), (2,2,11), (2,3,20);
INSERT INTO t VALUES (3,1,40), (3,2,40), (3,3,40);

SELECT * from t;

SELECT MAX(ABS(sup.x - inf.x))
FROM  (SELECT f, MAX(x) x from t WHERE id = 2 GROUP BY f) sup
      INNER JOIN (select f, MIN(x) x FROM t WHERE id = 1 GROUP BY f) inf ON sup.f = inf.f

在MenuDetail类中，我获得诸如项目名称，价格，数量的信息：

public class CartAdapter extends RecyclerView.Adapter<CartAdapter.CartViewHolder>
{

    Context context ;
    private List<Cart> cartList;
    private double price;

    public CartAdapter(Context context, List<Cart> cartList) {
        this.context = context;
        this.cartList = cartList;

    }

    @NonNull
    @Override
    public CartViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View itemView = LayoutInflater.from(context).inflate(R.layout.cart_item_layout, parent, false);
    //   CartViewHolder viewHolder = new CartViewHolder(itemView, mData);
        return new CartViewHolder(itemView);
    }

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

        double price = (Double.parseDouble(String.valueOf(cartList.get(position).price)) 
                            * Double.parseDouble(cartList.get(position).amount));

        holder.cart_menu_amount.setText(new StringBuilder(cartList.get(position).amount).append(" x"));
        holder.menu_name.setText(cartList.get(position).name);
        // holder.menu_price.setText((new StringBuilder(String.valueOf(cartList.get(position).price))));
        holder.menu_price.setText(new StringBuilder(String.valueOf(price)).append(" €"));

        double subTotal = 0;
        subTotal += (Double.parseDouble(String.valueOf(cartList.get(position).price)) 
                        * Double.parseDouble(cartList.get(position).amount));

        holder.total_price_cart.setText((int) subTotal);
    }

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

    public class CartViewHolder extends RecyclerView.ViewHolder {

        TextView menu_name;
        TextView menu_price;
        TextView cart_menu_amount;
        TextView total_price_cart;

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

            total_price_cart = (TextView)itemView.findViewById(R.id.total_price_cart);
            menu_name = (TextView)itemView.findViewById(R.id.cart_name);
            menu_price= (TextView)itemView.findViewById(R.id.cart_price);
            cart_menu_amount= (TextView) itemView.findViewById(R.id.cart_menu_amount);
        }
    }
}

Answer 1

使用调试器检查您要在其中设置小计的textView，可能未将其附加到xml视图。还要更改

holder.total_price_cart.setText（（int）小计）;

到

holder.total_price_cart.setText（String.valueOf（subTotal））;

settext方法中期望的

类型是字符串。

希望有帮助。

如何计算总和

1 个答案: