与 Service Worker 通讯link

Service worker communicationlink

把 ServiceWorkerModule 导入到你的 AppModule 中不仅会注册 Service Worker，还会提供一些服务，让你能和 Service Worker 通讯，并控制你的应用缓存。

Importing ServiceWorkerModule into your AppModule doesn't just register the service worker, it also provides a few services you can use to interact with the service worker and control the caching of your app.

前提条件link

Prerequisiteslink

对下列知识有基本的了解：

A basic understanding of the following:

• Service Worker 快速上手。

  Getting Started with Service Workers.

SwUpdate 服务link

SwUpdate servicelink

SwUpdate 服务让你能访问一些事件，这些事件会指出 Service Worker 何时发现了可用的更新或者一个更新何时可以被激活 —— 这意味着它现在可以通过更新后的版本提供服务了。

The SwUpdate service gives you access to events that indicate when the service worker has discovered an available update for your app or when it has activated such an update—meaning it is now serving content from that update to your app.

SwUpdate 服务支持四个独立的操作：

The SwUpdate service supports four separate operations:

• 获取出现可用更新的通知。如果要刷新页面，这些就是可加载的新版本。

  Getting notified of available updates. These are new versions of the app to be loaded if the page is refreshed.

• 获取更新被激活的通知。这时候 Service Worker 就可以立即使用这些新版本提供服务了。

  Getting notified of update activation. This is when the service worker starts serving a new version of the app immediately.

• 要求 Service Worker 向服务器查询是否有新版本。

  Asking the service worker to check the server for new updates.

• 要求 Service Worker 为当前标签页激活该应用的最新版本。

  Asking the service worker to activate the latest version of the app for the current tab.

有可用更新及已激活更新link

Available and activated updateslink

这两个更新事件 available 和 activated，都是 SwUpdate 的 Observable 属性：

The two update events, available and activated, are Observable properties of SwUpdate:

      
        content_copy
      
      @Injectable()
export class LogUpdateService {

  constructor(updates: SwUpdate) {
    updates.available.subscribe(event => {
      console.log('current version is', event.current);
      console.log('available version is', event.available);
    });
    updates.activated.subscribe(event => {
      console.log('old version was', event.previous);
      console.log('new version is', event.current);
    });
  }
}
    

你可以使用这些事件来通知用户有一个待做更新或当它们运行的代码已经过期时刷新页面。

You can use these events to notify the user of a pending update or to refresh their pages when the code they are running is out of date.

检查更新link

Checking for updateslink

可以要求 Service Worker 检查是否有任何更新已经发布到了服务器上。 Service Worker 会在初始化和每次导航请求（也就是用户导航到应用中的另一个地址）时检查更新。 不过，如果你的站点更新非常频繁，或者需要按计划进行更新，你可能会选择手动检查更新。

It's possible to ask the service worker to check if any updates have been deployed to the server. The service worker checks for updates during initialization and on each navigation request—that is, when the user navigates from a different address to your app. However, you might choose to manually check for updates if you have a site that changes frequently or want updates to happen on a schedule.

通过调用 checkForUpdate() 方法来实现：

Do this with the checkForUpdate() method:

      
        content_copy
      
      import { ApplicationRef, Injectable } from '@angular/core';
import { SwUpdate } from '@angular/service-worker';
import { concat, interval } from 'rxjs';
import { first } from 'rxjs/operators';

@Injectable()
export class CheckForUpdateService {

  constructor(appRef: ApplicationRef, updates: SwUpdate) {
    // Allow the app to stabilize first, before starting polling for updates with `interval()`.
    const appIsStable$ = appRef.isStable.pipe(first(isStable => isStable === true));
    const everySixHours$ = interval(6 * 60 * 60 * 1000);
    const everySixHoursOnceAppIsStable$ = concat(appIsStable$, everySixHours$);

    everySixHoursOnceAppIsStable$.subscribe(() => updates.checkForUpdate());
  }
}
    

该方法返回一个用来表示检查更新已经成功完成的 Promise，不过它不会指出是否确实发现了一个更新。 即使找到了一个，Service Worker 还必须成功下载更新过的文件，而这可能会失败。如果成功了，就会通过一个 available 事件来表明当前应用有一个可用的新版本。

This method returns a Promise which indicates that the update check has completed successfully, though it does not indicate whether an update was discovered as a result of the check. Even if one is found, the service worker must still successfully download the changed files, which can fail. If successful, the available event will indicate availability of a new version of the app.

强制激活更新link

Forcing update activationlink

如果当前标签页需要立即更新到最新的应用版本，可以通过 activateUpdate() 方法来要求立即这么做：

If the current tab needs to be updated to the latest app version immediately, it can ask to do so with the activateUpdate() method:

      
        content_copy
      
      @Injectable()
export class PromptUpdateService {

  constructor(updates: SwUpdate) {
    updates.available.subscribe(event => {
      if (promptUser(event)) {
        updates.activateUpdate().then(() => document.location.reload());
      }
    });
  }
}
    

关于 Angular Service Worker 的更多信息link

More on Angular service workerslink

你可能还对下列内容感兴趣：

You may also be interested in the following:

• 生产环境下的 Service Worker。

  Service Worker in Production.