AWS SDK iOS - how to determine the percentage completion of upload request

I'm trying to update a progress view as I upload an asset to an S3 bucket like so:

myTransferManager.upload(myTransferManagerRequest).continueWithExecutor(myDefaultThreadBFExecutor, withBlock: { (myBFTask) -> AnyObject! in ... etc etc. 

However, I can't figure out how to get the completion percentage of the request as it uploads. I have come across this delegate method a few times:

-(void)request:(AmazonServiceRequest *)request didSendData:(NSInteger)bytesWritten     totalBytesWritten:(NSInteger)totalBytesWritten totalBytesExpectedToWrite:    (NSInteger)totalBytesExpectedToWrite
{

}

But my project is written in Swift and I haven't been able to figure out how to implement this. For reference, I came across that method here: http://ift.tt/1xSuFm2 and here: Uploading to Amazon-S3 via AFNetworking

any tips would be greatly appreciated!

Cheers, Brendan