完整实现代码

1. 创建指令文件（推荐）

import Vue from 'vue'

Vue.directive('drag', {
	bind(el) {
		// 获取 Dialog 标题栏和内容区
		const dialogHeader = el.querySelector('.el-dialog__header')
		const dialogDrag = el.querySelector('.el-dialog')
		if (!dialogHeader || !dialogDrag) return

		// 鼠标样式
		dialogHeader.style.cursor = 'move'
		// 必须用 fixed 定位，才能自由拖动
		dialogDrag.style.position = 'fixed'

		// 每次打开弹窗 → 强制重置居中
		const resetCenter = () => {
			const clientWidth = document.documentElement.clientWidth
			const clientHeight = document.documentElement.clientHeight
			const dialogWidth = dialogDrag.offsetWidth
			const dialogHeight = dialogDrag.offsetHeight

			// 计算居中位置
			dialogDrag.style.left = (clientWidth - dialogWidth) / 2 + 'px'
			dialogDrag.style.top = (clientHeight - dialogHeight) / 2 + 'px'
			dialogDrag.style.margin = 0 // 清除 Element 默认居中
		}

		// 监听 Dialog 显示（每次打开都会重新居中）
		const ob = new MutationObserver(() => {
			if (el.style.display !== 'none') {
				resetCenter()
			}
		})
		ob.observe(el, { attributes: true, attributeFilter: ['style'] })

		// 拖拽逻辑
		dialogHeader.onmousedown = e => {
			const offsetX = e.clientX - dialogDrag.getBoundingClientRect().left
			const offsetY = e.clientY - dialogDrag.getBoundingClientRect().top

			document.onmousemove = moveEvent => {
				let left = moveEvent.clientX - offsetX
				let top = moveEvent.clientY - offsetY

				// 边界限制
				const maxLeft =
					document.documentElement.clientWidth -
					dialogDrag.offsetWidth
				const maxTop =
					document.documentElement.clientHeight -
					dialogDrag.offsetHeight
				left = Math.max(0, Math.min(left, maxLeft))
				top = Math.max(0, Math.min(top, maxTop))

				dialogDrag.style.left = left + 'px'
				dialogDrag.style.top = top + 'px'
			}

			document.onmouseup = () => {
				document.onmousemove = null
				document.onmouseup = null
			}
			e.preventDefault()
		}
	}
})

2. 在 main.js 全局注册

import Vue from 'vue'
import App from './App.vue'
import ElementUI from 'element-ui'
import 'element-ui/lib/theme-chalk/index.css'
// 引入拖拽指令
import './directives/drag'

Vue.use(ElementUI)
new Vue({
  el: '#app',
  render: h => h(App)
})

3. 在 Dialog 上使用 v-drag

<template>
  <div>
    <el-button @click="dialogVisible = true">打开可拖动 Dialog</el-button>

    <!-- 只需要加 v-drag 指令 -->
    <el-dialog
      v-drag
      title="可拖动对话框"
      :visible.sync="dialogVisible"
      width="500px"
    >
      <span>这是一个可以拖动的 Dialog ✨</span>
      <div slot="footer" class="dialog-footer">
        <el-button @click="dialogVisible = false">取消</el-button>
        <el-button type="primary" @click="dialogVisible = false">确定</el-button>
      </div>
    </el-dialog>
  </div>
</template>

<script>
export default {
  data() {
    return {
      dialogVisible: false
    }
  }
}
</script>