angular订阅update方法，什么时候需要取消订阅

import { Component, OnDestroy } from '@angular/core';
import { Subscription } from 'rxjs';

@Component({
  selector: 'app-example',
  template: '...'
})
export class ExampleComponent implements OnDestroy {
  private subscription: Subscription;

  constructor() {
    this.subscription = someObservable.subscribe(data => {
      // 处理数据更新
    });
  }

  ngOnDestroy() {
    this.subscription.unsubscribe();
  }
}

import { Component, OnInit } from '@angular/core';
import { Subscription } from 'rxjs';

@Component({
  selector: 'app-example',
  template: '...'
})
export class ExampleComponent implements OnInit {
  private subscription: Subscription;

  ngOnInit() {
    if (someCondition) {
      this.subscription = someObservable.subscribe(data => {
        // 处理数据更新
      });
    }
  }

  ngOnDestroy() {
    if (this.subscription) {
      this.subscription.unsubscribe();
    }
  }
}