loadTree() {
  this.auditItemTypeService
    .findAllTree()
    .pipe(
      switchMap((result: Array<TreeDto>) => {
        this.nodes = result;
        if (result && result.length) {
          // this.activeNode = this.nodes.find(item => {
          //   return item.key === this.activeNode.key;
          // });
          this.activeNode = this.findNode(this.nodes, this.currentItemId);
          if (!this.activeNode) {
            this.activeNode = this.nodes[0];
          }
          if (this.activeNode) {
            this.activeNode.selected = true;
            this.expandedKeys = [this.activeNode.key];
          }
          return this.auditItemTypeService.findById(this.activeNode.key);
        } else {
          this.activeNode = null;
          return of(null);
        }
      }),
    )
    .subscribe(res => {
      if (res) {
        this.isLeaf = false;
        this.auditItemTypeDetailComponent.edit(res);
        this.isEdit = false;
      }
    });
}

rxjs switchmap 应用案例