在这里，我调用了一个函数 addItem，在其中我增加了购物车的value

 <CartItem
                key={`cartItem-${item.item_id}`}
                onIncrement={() => addItem(item)}
                onDecrement={() => removeItem(item)}
                onRemove={() => removeItemFromCart(item)}
                data={item}
              />

我的上下文是

const addItemHandler = (item, quantity = 1) => {
    dispatch({ type: 'ADD_ITEM', payload: { ...item, quantity } });
  };

和我的 reducer 用于在 reducer.js 中添加项目

export const addItemToCart = (state, action) => {
  const existingCartItemIndex = state.items.findIndex(
    (item) => item.item_id === action.payload.item_id
  );
  if (existingCartItemIndex > -1) {
    const newState = [...state.items];
    newState[existingCartItemIndex].quantity += action.payload.quantity;
    return newState;
  }
  return [...state.items, action.payload];
};
const reducer = (state, action) => {
  switch (action.type) {
    case 'ADD_ITEM':
      return { ...state, items: addItemToCart(state, action) };
    default:
      throw new Error(`Unknown action: ${action.type}`);
  }
};

此代码将计数器增加 2 而不是增加 1。