If you have checked both the user keychain and the system keychain for old passwords, we're left with obscure guesses.
Two things come immediately to mind (from the obscure side).
- Your mac will join any base station with that SSID. I have seen people literally setting up a second router in busy coffee shops - you have to hold the option key and make note of the mac address you have connected to and see it change to catch this.
- If your wifi connects to the router wifi, it doesn't mean the dhcp server has any more addresses to lease. You will need the owner to reset or power cycle the router to see if the leases are all out and unexpired. You basicall have a great pipe connecting you to the main, but no water is flowing to you until you get a lease.
Unfortunately, on the iPhone it is not possible to access this information. The passwords are kept on your phone in a safe place that is not accessible through any regular means on the phone. This is done for your protection, if you were to lose your iPhone and someone picked it up, the passwords that are stored on it would be up for grabs. This would lead to a lot of security problems.
I would recommend apps like 1password or the many other pieces of software out there that do the same thing to keep your passwords safe and backed up. I have way to many passwords to remember and it has been a life saver. 1Password even has the ability to back up your passwords to dropbox just in case something happens to your phone and you need to access it from somewhere else.
There are a lot of different password managing apps out there, just find the right one for you.
As gtm above me stated, there is a way to access your passwords but it is through jailbreaking. I do not recommend jailbreaking, that is something that you have to make the decision on for yourself. Jailbreaking is not for everyone.
I know this may not have been the answer you were looking for, we have all been there when we forget a password and there isn't a way to retrieve it. The easier thing you can do is just reset the password on your router and make sure to keep that password safe.
I hope this answer helps somewhat.
Best Answer
"after reset my device 'view saved wifi passwords on the iPhone' " answers your question I think? Do you have a mac that's connected to the same network? Then you can retrieve the password in the Keychain of the computer. (analogue for Windows systems)