一、实现思路

动态设置高度和宽度，高度很容易，就是el-tree本身的高度，困难点是如何找到应该设置的宽度，我的思路是直接强行取到一级节点及其展开节点中最宽的一个元素，取这个元素的宽度，来动态设置整个容器的宽度。

二、实现过程

1.监视元素el-tree内部改变，封装hooks

首先是如何监视元素的宽高度改变，这里我们实现一个监视元素宽高改变的hooks

具体Api文档：developer.mozilla.org/zh-CN/docs/…

useResizeObserver.ts

import { onMounted, onUnmounted, ref } from "vue";
import * as _ from "lodash";
const { isString, throttle } = _;

/**
 * ResizeObserver 构造函数创建一个新的 ResizeObserver 对象，它可以用于监听 Element 内容盒或边框盒或者 SVGElement 边界尺寸的大小。
 * @param el
 * @param callback
 * @param config
 */
const useResizeObserver = (
  el: HTMLElement | string,
  callback: (mutationList: ResizeObserverEntry[]) => void = () => {},
  config: {
    throttleTime: number;
  } = { throttleTime: 0 }
) => {
  const observer = ref<ResizeObserver>();
  const observerCallback = throttle(callback, config.throttleTime);
  /**
   *
   * @param el {HTMLElement}  需要观察的元素
   */
  const creatObserver = function (el: HTMLElement) {
    if (!el) return;
    // 选择需要观察变动的节点
    const targetNode = el;

    // 创建一个观察器实例并传入回调函数
    const observer = new ResizeObserver(observerCallback);

    // 以上述配置开始观察目标节点
    observer.observe(targetNode);
    return observer;
  };
  onMounted(() => {
    const targetObserverEl = isString(el)
      ? (document.querySelector(el) as HTMLElement)
      : el;
    if (targetObserverEl) {
      observer.value = creatObserver(targetObserverEl);
    }
  });

  onUnmounted(() => {
    observer.value?.disconnect?.();
  });
  return {
    observer,
  };
};
export default useResizeObserver;

2.开始封装组件

文件目录结构

ScrollTree.ts

import { buildProps } from "element-plus/es/utils/index.mjs";

export const ScrollTreeProps = buildProps({
  height: {
    type: [Number, String],
    default: "100%",
  },
  width: {
    type: [Number, String],
    default: "100%",
  },
} as const);

ScrollTree.vue

<template>
  <div
    :class="wrapClassName"
    :style="{
      width: isNumber(props.width) ? props.width + 'px' : props.width,
      height: isNumber(props.height) ? props.height + 'px' : props.height,
      overflow: 'scroll',
    }"
  >
    <div
      :class="className"
      :style="{
        width: width,
        height: height,
      }"
      style="overflow: hidden"
    >
      <el-tree v-bind="$attrs">
        <!-- 遍历子组件作用域插槽，并对父组件暴露 -->
        <template v-for="(index, name) in $slots" v-slot:[name]="data">
          <slot :name="name" v-bind="data"></slot>
        </template>
      </el-tree>
    </div>
  </div>
</template>
<script lang="ts" setup>
import { defineProps, ref } from "vue";
import useResizeObserver from "../../../hooks/src/useResizeObserver";
import { ScrollTreeProps } from "./ScrollTree";
import * as _ from "lodash";
const { isNumber, uniqueId } = _;
// 解决浏览器审查模式下 最外层额外显示的props
defineOptions({
  inheritAttrs: false,
});
//#region <实现>
const className = uniqueId("my-scroll-tree");
const wrapClassName = uniqueId("my-scroll-tree-wrap");
const props = defineProps(ScrollTreeProps);
// 应该设置的高度
const height = ref("100%");
const width = ref("100%");
const callback = (entries: ResizeObserverEntry[]) => {
  // 寻找高度
  const newHeight = entries?.[0].borderBoxSize?.[0]?.blockSize;
  height.value = newHeight ? newHeight + "px" : "100%";
  //   寻找宽度
  let maxWidth = 0;
  let maxPaddingLeft = 0;
  let checkBoxWidth = 0;
  const treeDom = entries?.[0]?.target;
  Array.from(treeDom?.children).forEach((item: HTMLElement) => {
    getWidth(item);
  });
  // 是否存在checkbox
  const checkbox = document.querySelector(
    `.${wrapClassName} .${className} .el-tree .el-tree-node__content .el-checkbox`
  ) as HTMLElement;
  if (checkbox) {
    const checkBoxMargin =
      +getElNodeAttrValue(checkbox, "margin-right")?.split("px")?.[0] || 0;
    const checkBoxClientWidth = checkbox.clientWidth;
    checkBoxWidth = checkBoxMargin + checkBoxClientWidth;
  }
  // 寻找最小宽度
  const minWidthNode = document.querySelector(`.${wrapClassName}`);
  const minWidth = minWidthNode?.clientWidth || 0;
  const targetWidth = maxWidth + maxPaddingLeft + checkBoxWidth;
  width.value = isNumber(targetWidth)
    ? (targetWidth > minWidth ? targetWidth : minWidth) + "px"
    : "100%";
  function getWidth(el: HTMLElement) {
    const elWidthNode = Array.from(el.children).find((item) => {
      return Array.from(item.classList || []).includes("el-tree-node__content");
    }) as HTMLElement;
    if (elWidthNode) {
      const paddingLeftValue =
        +getElNodeAttrValue(elWidthNode, "padding-left")?.split("px")?.[0] || 0;
      let elWidthNodeList = elWidthNode?.children || ([] as HTMLElement[]);
      let elWidth = 0;
      // 获取padding
      Array.from(elWidthNodeList).forEach((item) => {
        elWidth += item.clientWidth;
      });

      maxWidth = maxWidth > elWidth ? maxWidth : elWidth;
      maxPaddingLeft =
        maxPaddingLeft > paddingLeftValue ? maxPaddingLeft : paddingLeftValue;
    }

    if (el.ariaExpanded === "false") {
      return;
    }
    if (el.children) {
      Array.from(el.children).forEach((item: HTMLElement) => {
        getWidth(item);
      });
    }
  }
};
useResizeObserver(`.${wrapClassName} .${className} .el-tree`, callback, {
  throttleTime: 0,
});
const getElNodeAttrValue = (el: HTMLElement, attrKey: string) => {
  const computedStyles = getComputedStyle(el);
  return computedStyles.getPropertyValue(attrKey) as string;
};
//#endregion
</script>

三、实现效果

实现效果代码

<template>
  <div>
    <h2>直接使用设置宽高</h2>
    <ScrollTree :data="data" :props="props" :height="200" :width="500" />
    <h2>直接使用不设置宽高</h2>
    <ScrollTree :data="data" :props="props" />
    <h2>父组件设置宽高</h2>
    <div style="width: 500px; height: 200px">
      <ScrollTree :data="data" :props="props">
        <template #default="{ node }">
          <span>{{ node.label }}</span>
        </template>
      </ScrollTree>
    </div>
  </div>
</template>
<script lang="ts" setup>
import { ScrollTree } from "../../../packages";
interface Tree {
  id: string;
  label: string;
  children?: Tree[];
}

const getKey = (prefix: string, id: number) => {
  return `${prefix}-${id}-测试测试测试测试测试测试测试测试测试测试测试测试测试测试测试测试测试测试测试测试测试测试测试测试测试测试测试测试测试测试测试测试测试测试测试测试测试测试测试测试测试测试测试测试测试测试测试测试测试测试测试测试测试测试测试测试测试测试测试测试测试测试测试测试--`;
};

const createData = (
  maxDeep: number,
  maxChildren: number,
  minNodesNumber: number,
  deep = 1,
  key = "node"
): Tree[] => {
  let id = 0;
  return Array.from({ length: minNodesNumber })
    .fill(deep)
    .map(() => {
      const childrenNumber =
        deep === maxDeep ? 0 : Math.round(Math.random() * maxChildren);
      const nodeKey = getKey(key, ++id);
      return {
        id: nodeKey,
        label: nodeKey,
        children: childrenNumber
          ? createData(maxDeep, maxChildren, childrenNumber, deep + 1, nodeKey)
          : undefined,
      };
    });
};

const props = {
  value: "id",
  label: "label",
  children: "children",
};
const data = createData(3, 3, 10);
</script>
<style scoped lang="scss"></style>