Error handling for cancelled request

Question

I use Alamofire to send a download request. I am handling Success and Failure cases as shown below.

Alamofire.request {
     case Success:
          // Update UI
     case Failure:
          // Show Alert message (error!.localizedDescription)
}

Everything is perfectly fine.

When I go back, in viewWillDisappear, I cancel any ongoing request. The issue is, canceling the request throws the error message and that triggers the alert when I am not on that screen.

To my knowledge, I can take two actions.

1. Check the condition if the error is created due to request cancel
2. Check if the viewController is alive
3. Also I can set a Bool variable in viewWillDisappear, which is a simple solution

How to handle the situation?

Also how to check point 1 & 2?

Answer 1

This is a more generic approach which works for any device language:

Swift 4

if (response.error as NSError?)?.code == NSURLErrorCancelled {
   // Do Your stuff
}

Answer 2

NOTE: Use aumanets answer for failsafe check

For the ppl who are wondering how to use the option 1

you can check the request cancelled error to find if the request is cancelled

let errorDict = (error as NSError).userInfo;
if let errorString = errorDict["NSLocalizedDescription"] as? String, errorString == "cancelled" {
    // Request is cancelled.
}

This answer is derived from @peres's answer.