开发的APP ,再打开部分页面后，占用内存随着时间延长不断增加，是什么原因？

<template>
<view class="body1">

            <view class="grid-item" v-for="(item, index) in productCategoryList" :key="index" >  
                <view class="grid-item-box" @click="navToChildrenPage(item)">     
                    <image :src="getImgUrl(item.Icon)" lazy-load="true" mode="aspectFill"></image>  
                    <text class="text">{{ item.Name }}</text>  
                </view>  
            </view>  
       <!-- <uni-grid :column="col" @change="change" >  
            <uni-grid-item class="grid-item" v-for="(item, index) in productCategoryList" :key="index" >  
                <view class="grid-item-box" @click="navToChildrenPage(item)">  

                    <image :src="getImgUrl(item.Icon)" lazy-load="true" mode="aspectFill"></image>  
                    <text class="text">{{ item.Name }}</text>  
                </view>  
            </uni-grid-item>  
        </uni-grid> -->  
</view>  

</template>

<script>
// import uniIndexedList from '@/components/uni-indexed-list/uni-indexed-list.vue';
// import uniGrid from '@/components/uni-grid/uni-grid.vue';
// import uniGridItem from '@/components/uni-grid-item/uni-grid-item.vue';
// import { mapMutations } from 'vuex';
export default {
// components: { uniIndexedList,
// uniGrid,
// uniGridItem,},
data() {
return {
productCategoryList: [],
col:3
};
},

onLoad() {  
    this.getProductCategoryList();  
},  
onShow()  
{  
    let _this = this  
    uni.getSystemInfo({  
        success: function(res) {  
            if (res.windowWidth > res.windowHeight) {  
                // 横屏  
                _this.col=6;  
            } else {  
                // 竖屏  
                _this.col=3;  
            }  
        }  
    });  
},  
// onHide()  
// {  
//     this.productCategoryList=[];  
// },  
onUnload()  
{  
    this.productCategoryList=[];  
},  
methods: {    
    change(e) {  
        let { index } = e.detail;  
        //console.log(index);  
    },  
    getProductCategoryList() {  
        let that = this;  
        uni.request({  
            url: this.$store.state.siteBaseUrl + '/api/Shop/GetProductCategories?parentId=5',  
            data: {},  
            method: 'GET',  
            header: {  
                Authorization: this.$store.state.userInfo.result.Token,  
                'content-type': 'application/json'  
            },  
            success: function(res) {  
                that.productCategoryList = res.data.result;  
            }  
        });  
    },                
    getImgUrl(icon) {  
        if (icon) return this.$store.state.imgSiteUrl + icon;  
        else return '/static/list.png';  
    },  
    navToChildrenPage(item) {  
        uni.navigateTo({  
            url: `/pages/category/productcategory1?item=${JSON.stringify(item)}`  
        });  
    },  
},  

};
</script>
<style lang="scss">
page {
background: #f5f5f5;

}  
.body1{  

}  
.grid-item  
{  

padding: 8upx 8upx;  
width: 16%;  
float:left;  
position:relative;  
.grid-item-box {  
    flex: 1;  
    /* position: relative;  
            */  
    /* #ifndef APP-NVUE */  
    display: flex;  
    /* #endif */  
    flex-direction: column;  
    align-items: center;  
    justify-content: center;  

    border-radius: 8upx;  
    // margin: 8upx;  
    border: 0upx;  
    background: rgba(174, 221, 229, 0.8);  
    /* 原图标颜色太深,不想改图了,所以加了透明度 */  
    image {  
        width: 64upx;  
        height: 64upx;  
        margin: 7upx;  

        border-radius: 50%;  
        opacity: 0.7;  
        box-shadow: 4upx 4upx 20upx rgba(250, 67, 106, 0.3);  
    }  
    text {  
        width: 80upx;  
        padding: 8upx 2upx;  
        text-align: center;  
        font-size: 13upx;  
    }  
}  
}  

</style>