Set & Get

组件传值，监听数据修改；

// 组件接收一个userId值
<app-user-list [userId]="userId"></app-user-list>

export class UserListComponent {
  // ...
  @Input() userId: number;
  // ...
}

export class UserListComponent {
  private _userId: number;

  @Input()
  set userId(userId: number) {
    this._userId= userId;
  }

  get userId(): number{ return this._userId; }
}