vue中v-for循环时增加校验

html：

        <el-form-item v-if="['1','2'].includes(form.themeType)" label="文案">
          <div class="picTopic">
            <template v-if="form.contentList.length!==0">
              <el-col v-for="(item,index) in form.contentList" :key="index" :span="6">
                <div class="picTopicInput">
                  <el-form-item :prop="'contentList.'+index+'.copywritingContent'" :rules="formRules.copywritingContent">
                    <el-input
                      v-model="item.copywritingContent"
                      type="textarea"
                      :rows="3"
                      resize="none"
                      placeholder="请输入文案，限制在250字以内"
                    />
                  </el-form-item>
                  <i class="el-icon-circle-close" @click="picTopicDelete(item)" />
                </div>
              </el-col>
            </template>
            <el-col :span="2" :offset="1">
              <el-button icon="el-icon-plus" @click="picTopicAdd" />
            </el-col>
          </div>
        </el-form-item>

js: 

    formRules: {       
        copywritingContent: [
          {
            min: 1,
            max: 250,
            message: '文案长度不能超过250个汉字字符！',
            trigger: 'blur'
          }
        ]
    }