el-tree刷新节点收缩问题解决

el-tree刷新时会初始化绑定数据，可设置el-tree的默认展开节点，还原刷新前展开状态

:default-expanded-keys="defaultExpandNodes"

在调用el-tree绑定数据刷新时执行以下方法保存当前节点展开状态即可

setDefaultExpandedKeys() {
      let treeCompInstance = this.$refs["tree"];
      let allNodes = treeCompInstance.store._getAllNodes();
      let defaultExpandNodes = [];
      allNodes.forEach((node) => {
        node.expanded && defaultExpandNodes.push(node.data.treeId);
      });
      this.defaultExpandNodes = defaultExpandNodes;
},