vue项目中点击打开弹窗，弹窗上面有子组件，在点击打开弹窗的方法中使用this.$refs却获取不到子组件的ref值：

简易代码如下： 

<a-modal centered v-model="visible" :title="title">
   <upload ref="upload" />
</a-modal>

js:

        handleOpenUpload(){
            this.visibleUpload = true;
            console.log('refs',this.$refs.upload); //获取不到
        }

解决：

handleOpenUpload(){
            this.visibleUpload = true;
            this.$nextTick(() => {
                console.log('refs',this.$refs.upload);//能获取
            });
        }