借助Flutter和Firebase实现实时的在线/离线状态

问题描述：

您好，如果用户在线或离线，在应用中显示的最佳方式是什么?

Hy, what is the best way to show in an app if the user is online or offline?

前端->颤振

后端-> Firestore云和Firebase身份验证.

Backend -> Firestore Cloud and Firebase Auth.

我在Firestore中有一个包含文档的用户集合.每个文档都是用户，并且包含状态"字段.很快，我可以在用户每次登录或注销时更新此字段，但是如果您关闭该应用程序，则该字段不会更新.

I have a collection of users in firestore that contains documents. Each document is a user and contain "status" field. In flutter i can update this field every time that user sign in or log out but if you close the app it is not updated.

答

您可以使用 WidgetsBindingObserver 扩展statefulWidget State类像

You can extend your statefulWidget State class with WidgetsBindingObserver like

class _HomePageState extends State<HomePage>
    with WidgetsBindingObserver

和 initState 方法添加 WidgetsBinding.instance.addObserver(this); .

@override
  void initState() {
    super.initState();
    WidgetsBinding.instance.addObserver(this);
  }

稍后覆盖 didChangeAppLifecycleState 方法

@override
  void didChangeAppLifecycleState(AppLifecycleState state) {
    if (state == AppLifecycleState.resumed)
      //TODO: set status to online here in firestore
    else
      //TODO: set status to offline here in firestore
  }

借助Flutter和Firebase实现实时的在线/离线状态

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