javascript - vue 获取v-for渲染数据多维数组出错

<p class="content clearfix" :class='{active: isActive}'>
            <ul>
                <li v-for='item in items' :key=item>
                    <p>
                        <img :src="item.picList[0].imgurl"  alt="item.t_name">
                        <p>{{item.title}}</p>
                        <span>{{item.datanum}}张</span>
                    </p>
                </li>
            </ul>
        </p>

initData () {
                let _this = this;
                // this.loading = true;
                this.$http.get('xxxxxxxxxxx', {
                    params: {
                        'key': '56b12e3f238be',
                        'pageSize': '8',
                        'a_no': '001',
                        'classify': '01'
                    }
                }).then((res) => {
                    _this.items = res.body.result;
                    console.log(_this.items);
                    // 异步更新队列
                    _this.$nextTick(function () {
                        let imgs = document.querySelectorAll('li>p>img');
                        console.log(imgs);
                        let num = 0;
                        for (var i = 0; i < imgs.length; i++) {
                            imgs[i].onload = function () {
                                num++;
                                // console.log(num);
                                if (num === imgs.length) {
                                    _this.waterfull();
                                    // _this.isShow = true;
                                    // _this.loading = false;
                                    _this.isActive = true;
                                    console.log(_this.loading);
                                }
                            };
                        };
                    });
                    // console.log(_this.items);
                }, (err) => {
                    console.log(err);
                });
            },

通过$nextTick（）方法获取items改变后的dom元素，本来好好的，可以获取的，后来也没调啥啊啊啊啊 啊啊，发现无法获取了，根本不渲染了啊啊啊啊啊啊啊啊啊啊，回滚后也一样，日日日日日！！！！什么鬼啊啊啊啊啊

initData () {

            let _this = this;
            // this.loading = true;
            this.$http.get(xxxxxxxxxxx, {
                params: {
                    'key': '6b12e3f238be',
                    'pageSize': '8',
                    'a_no': '001',
                    'classify': '01'
                }
            }).then((res) => {
                _this.items = res.body.result;
                console.log(_this.items[0].picList);
                for (var k = 0; k < _this.items.length; k++) {
                    var imgurl = _this.items[k].picList[0].imgurl;
                    console.log(imgurl);  //这一行能打印出来，但vue在上一行却报错
                    _this.items[k].imgurl = imgurl;
                };
                // 异步更新队列
                _this.$nextTick(function () {
                    let imgs = document.querySelectorAll('li>p>img');
                    console.log(imgs);
                    let num = 0;
                    for (var i = 0; i < imgs.length; i++) {
                        imgs[i].onload = function () {
                            num++;
                            // console.log(num);
                            if (num === imgs.length) {
                                _this.waterfull();
                                // _this.isShow = true;
                                // _this.loading = false;
                                _this.isActive = true;
                                console.log(_this.loading);
                            }
                        };
                    };
                });
                console.log(_this.items);
            }, (err) => {
                console.log(err);
            });
        },