微信小程序外卖选购页实现切换分类与数量加减功能案例

categoryStates = categoryStates.map(function (item, i) {
if (index == i) {
item = true;
} else {
item = false;
}
return item;
});

class="{{categoryStates[index] ? 'category-item-active' : ''}}"

add: function (e) {
// 所点商品id
var foodId = e.currentTarget.dataset.foodId;
console.log(foodId);
// 读取目前购物车数据
var cartData = that.data.cartData;
// 获取当前商品数量
var foodCount = cartData[foodId] ? cartData[foodId] : 0;
// 自增1后存回
cartData[foodId] = ++foodCount;
// 设值到data数据中
that.setData({
cartData: cartData
});
}

<view class="stepper">
<!-- 减号 -->
<view class="symbol subtract" wx:if="{{cartData[item.objectId]}}">-</view>
<!-- 数量 -->
<view class="value">{{cartData[item.objectId]}}</view>
<!-- 加号 -->
<view class="symbol add" bindtap="add" data-food-id="{{item.objectId}}">+</view>
</view>

subtract: function (e) {
// 所点商品id
var foodId = e.currentTarget.dataset.foodId;
// 读取目前购物车数据
var cartData = that.data.cartData;
// 获取当前商品数量
var foodCount = cartData[foodId];
// 自减1
--foodCount;
// 减到零了就直接移除
if (foodCount == 0) {
delete cartData[foodId]
} else {
cartData[foodId] = foodCount;
}
// 设值到data数据中
that.setData({
cartData: cartData
});
}