用户已经保持身份验证。重新启动应用程序后，Firebase从磁盘读取凭据，并刷新用户的令牌。由于这需要往返服务器，因此它是异步发生的。因此，请确保等待_auth.currentUser（）来获取用户状态的通知。

Users already stay authenticated. After you restart the app, Firebase reads the credentials from disk, and refreshes the user's token. Since this requires a roundtrip to the server, it happens asynchronously. So be sure to await _auth.currentUser() to get notified of the user's status.

无论何时我想知道如何做这些事情，我看了 FlutterFire示例应用程序。可以在此处找到此行。

Whenever I'm wondering how to do such things, I look at the FlutterFire sample app. This specific line can be found here.