element el-input的autofocus失效问题解决

需求：下拉新增row, 最后一个定位focus

<el-table
          :data="infoData.itemList"
          fit
          header-cell-class-name="cellClass"
          row-class-name="rowClass"
        >
          <el-table-column v-if="userType === 2" width="50">
            <template slot-scope="{$index}">
              <div class="control-row">
                <div @click="deleteRowData($index)">-</div>
              </div>
            </template>
          </el-table-column>
          <el-table-column prop="sampleName" label="序号" align="center" width="63" >
            <template slot-scope="{$index}">
              <el-input :value="$index + 1" disabled="true"/>
            </template>
          </el-table-column>
          <el-table-column prop="sampleName" label="样品名称">
            <template slot-scope="{row, $index}">
              <el-input v-model="row.sampleName" placeholder="请输入" :disabled="checkId(row.id)" :ref="'rowInput' + $index" />
            </template>
          </el-table-column>



    // 新增行
    addRowData() {
      this.infoData.itemList.push({
        sampleName: '', // 样品名称
        detectionProject: '', // 检测项目
        standard: '', // 标准
        consequence: '', // 结果
        isQualified: 1, // 是否合格 ( 0: 是，1：否 )
        actionResults: '通过', // 处置措施
        detectionUser: '' // 检测人
      })
      const len = this.infoData.itemList.length - 1
      this.$nextTick(() => {
        this.$refs['rowInput' + len].$refs.input.focus();
      })
    },