NSURLSession didCompleteWithError:gets called with

Question

Scenario is taking the app to background and foreground multiple times when its uploading is in progress,didCompleteWithError: method is called while taking app to foreground with error parameter is null. Probabilty is 1/3.

How do i find out what went wrong as error parameter does not give anything.

Answer 1

The problem is that didCompleteWithError report only client side error, otherwise is nil. iOS doc said:

"Server errors are not reported through the error parameter. The only errors your delegate receives through the error parameter are client-side errors, such as being unable to resolve the hostname or connect to the host."

This is the link to the documentation.

If you want to check session's errors you have to implement session protocol delegate

- URLSession:didBecomeInvalidWithError:

Remember to invalidate the session after stop using it. So if you create an NSURLSession like this:

NSURLSessionConfiguration *backgroundConfigurationObject = [NSURLSessionConfiguration backgroundSessionConfigurationWithIdentifier:@"applycasession"];
    self.backgroundSession = [NSURLSession sessionWithConfiguration:backgroundConfigurationObject delegate:self delegateQueue:[NSOperationQueue mainQueue]];

When you finish to use it you have to call:

 [self.backgroundSession invalidateAndCancel];

Please read the documents about "Life Cycle of URL Session" at this link