如果ngFor中的active属性为true，如何获取成员长度

export class YourComponent {
  members = [
    { name: 'Member 1', active: true },
    { name: 'Member 2', active: false },
    { name: 'Member 3', active: true },
    { name: 'Member 4', active: true },
  ];

  activeMembersLength: number;

  constructor() {
    this.activeMembersLength = this.members.filter(member => member.active).length;
  }
}

<p>活动成员的长度为：{{ activeMembersLength }}</p>