问题
I am using Indy to connect to an Ftp server. We have had problems with the server being down, creating a "Host not found" error, which I handle and indicate to the user, however, today the software was installed on a computer that did not have an internet connection. The error produced when I "Connect" is also "Host not found", which is not totally correct. Is there a function/procedure I can call inside the TIdFtp component that will tell me if there is actually a connection to the internet so I can display an error indicating the user is not connected? I am using Delphi XE Seattle.
I have looked through the list of IdFtp properties/functions etc, but nothing seems obvious.
回答1:
Is there a function/procedure I can call inside the TIdFtp component that will tell me if there is actually a connection to the internet so I can display an error indicating the user is not connected?
No. What you will have to do is attempt a TCP connection to several different servers and see if any of them succeed or if they all fail. For instance, you can use TIdTCPClient to connect to well-known server ports that are pretty much guaranteed to be online 99+% of the time, like google.com/yahoo.com on port 80 (HTTP) or 443 (HTTPS), etc.
来源：https://stackoverflow.com/questions/57213954/how-can-i-check-i-am-actually-connected-to-the-internet