vue3获取元素高度不准

<transition name="slide-width">
    <a-col class="fixed-small" v-show="isShow" :style="{height: `${ztreeHeight}px`}">
         <div style="height: 500px; ">
             555
         </div>
    </a-col>
</transition>
<a-col class="auto-small-full" :class="{ 'auto-small': isShow }" ref="rightBox">
    <a-table
        :size="state.tableSize"
        :loading="state.loading"
        :columns="dynamicColumns"
        :data-source="state.dataSource"
        :scroll="{ x: 1800 }"
        :pagination="{
        current: state.current,
        pageSize: state.pageSize,
        total: state.total,
        size: 'middle',
        showTotal: total => `共 ${total} 条`,
    }"
        @change="handleTableChange"
    >
        <template #statusOther="{ text }">
            <a-tag :color="statusMap[text].status">
                {{ statusMap[text].text }}
            </a-tag>
        </template>
        <template #action="{ text, record }">
            <a :title="text" @click="detailFuns(record)">查看详情</a>
        </template>
    </a-table>
</a-col>

const rightBox = ref();
let ztreeHeight = ref<number>(0);
 
onMounted(() => {
    watch(
        () => state.dataSource,
        () => {
            nextTick(()=>{
               $(document).ready(()=>{
                   ztreeHeight.value = rightBox.value.$el.scrollHeight;
               })
            })
 
        },
    );
});

<el-form :model="addOrEditForm" class="el-form-dialog" label-width="120px" ref="elForm" >
</el-form>

this.refs.elForm.$el.offsetHeight