网络请求成功了，数据也打印出来了，但是不能渲染ui

getInvoiceData: function() {
var mobileNum =
"ACMjAyMDA2MjkxNzMyMzgzMTUwMTAwMTM0w93KdABclN9a/TxRqCAnTwhXDfiCKWPjNMnUGqjJm546CQM5JFoAnPbhOQtCsdQskoYfugMYAvlmbyUJW/cgdKOutBUfBcDO";
var billingCycleStart = "202001";
var billingCycleEnd = "202006";

            this.loading = true  
            this.$api.getInvoiceData({  
                mobileNum: mobileNum,  
                billingCycleStart: billingCycleStart,  
                billingCycleEnd: billingCycleEnd  
            }).then((res) => {  
                this.loading = false;  
                console.log('request success', res.data)  
                uni.showToast({  
                    title: '请求成功',  
                    icon: 'success',  
                    mask: true  
                });  
                this.res = '请求结果 : ' + res;  
                this.itemList = JSON.parse(res.data).list;  
                console.log(this.itemList)  
            }).catch((err) => {  
                this.loading = false;  
                console.log('request fail', err);  
            })  
        }