OnDisconnect() nerver fire

Question

as the title, I use OnDisconnect to make presence feture. I did a test :

1. I open app when has internet connection -> it works fine and the user online now.
2. I turn off the internet ( both Cellular and Wifi ) and close the app -> the OnDisconnect should fire in a few minutes, but it did not.

I read this post : Firebase: when onDisconnect event fire?

是什么

@Frank说：“所以在这种情况下，您只需要多一点耐心即可。”但是我已经等了一个小时，它仍然没有启动。

那么我们应该等多久呢？至少我们怎么知道它会发射还是不发射？

这是我的代码：

  if (getMyUID()!=null){
            ROOT_REF.child(CHILD_USERS)
                    .child("userid")
                    .child("active").setValue(Calendar.getInstance().getTimeInMillis()+"");

            ROOT_REF.child(CHILD_USERS)
                    .child("userid")
                    .child("active").onDisconnect()
                    .setValue(Calendar.getInstance().getTimeInMillis()+"");
        }