关闭应用程序时，布尔值不设置为no

I use Firebase in the application. I want to record the user's status in the database, it is currently in the application or not. I use the code from the official document, which must ensure this task. When the application is opened, the value is set to NO, and then changed to YES. But at the close of the application as well as the transition to the background, the block is not called and the value does not change. Here is my code...I use Firebase in the application. I want to re