需要实现这样的效果，即 toast 消息提示框在 popup 下拉框之上：

解决方法，把 <u-toast ref="uToast" /> 放在 u-popup 里面即可，这样就可以提升 toast 的优先级：

html"><!-- 弹出下拉框 -->
			<u-popup :show="evaluateShow" @close="evaluateClose" @open="evaluateOpen">
				<div>
					<u-toast ref="uToast" />
					<div style="padding: 10px;border-bottom: 1px solid #f5f5f5;">评价分数</div>
					<u-textarea style="padding: 10px;" v-model="scoreVal" placeholder="请输入内容"></u-textarea>
					<div style="padding: 10px;border-bottom: 1px solid #f5f5f5;">作业评价</div>
					<u-textarea style="padding: 10px;" v-model="workVal" placeholder="请输入内容"></u-textarea>
					<u-upload style="padding: 10px;" :fileList="picList" @afterRead="afterRead"
						@delete="deletePic"></u-upload>
					<u-button type="primary" text="提交" @click="evaluateReasonClick"
						style="background-color: #0081CC;"></u-button>
				</div>
			</u-popup>