Swift wait for existing async operation to finish before starting a new one

Question

I'm working on a Swift project that uses token based authentication. When the application resumes from the background the the AppDelegate function applicationWillEnterForeground() does a check to make sure the token in memory hasn't expired (expiry date is stored in NSUserDefaults and in the token_expiry variable). If it has expired, it'll call a function to renew and get a new one.

The problem i'm facing is that while the async function is waiting for the server to reply with a new token, the user in the app could do something which requires authorisation. If this happens, since a new token has not been acquired yet the app will query the server using the old token value and data will not be retrieved.

Is there a way to ensure that the async function to renew the token has finished before we do anything else?

Answer 1

Set up a system of NSNotifications to inform your GUI when authentication is valid/invalid.

In your GUI, enable or disable the user controls that need authentication as appropriate when the notifications occur. How you do this will depend on your GUI design: hiding controls, greying out controls and activity indicators are some options.

Send these notifications as appropriate when you check authentication.