在Swift中下载NSURLSession期间未调用URLSession委托

Question

I'm trying to use a delegate method to update a progress bar as a file is downloaded using NSURLSession , however I can't seem to get the Delegate method to call.

The delegate method I have is as follows in Swift (doesn't get called when file download is initiated):

func URLSession(session: NSURLSession, downloadTask: NSURLSessionDownloadTask, didWriteData bytesWritten: Int64, totalBytesWritten: Int64!, totalBytesExpectedToWrite: Int64){

    println("delegate called")
    if (totalBytesExpectedToWrite == NSURLSessionTransferSizeUnknown) {
        println("Unknown transfer size")
    } else {
        let index: Int = self.getFileDownloadInfoIndexWithTaskIdentifier(downloadTask.taskIdentifier)
        let fdi: FileDownloadInfo = self.arrFileDownloadData.objectAtIndex(index) as FileDownloadInfo
        NSOperationQueue().addOperationWithBlock({

            //Calculate the progress
            fdi.downloadProgress = Double(totalBytesWritten) / Double(totalBytesExpectedToWrite)

            // Update the progressview bar
            self.progressView.progress = Float(fdi.downloadProgress)

        })

    }
}

The equivalent Objective-C call I'm trying to replicate in Swift above is (which DOES get called when file download is initiated):

-(void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didWriteData:(int64_t)bytesWritten totalBytesWritten:(int64_t)totalBytesWritten totalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite{

    NSLog(@"Delegate called");
    if (totalBytesExpectedToWrite == NSURLSessionTransferSizeUnknown) {
        NSLog(@"Unknown transfer size");
    }
    else{
        // Locate the FileDownloadInfo object among all based on the taskIdentifier property of the task.
        int index = [self getFileDownloadInfoIndexWithTaskIdentifier:downloadTask.taskIdentifier];
        FileDownloadInfo *fdi = [self.arrFileDownloadData objectAtIndex:index];

    [.............]
        }];
    }
}

I'm sensing that I am doing something wrong as although, in both cases, I don't get the autofill filling in with the variables I need access to (eg didWriteData , bytesWritten etc), in ObjectiveC, after I type -(void)URLSession:(NSURLSession *)session , I get downloadTask and didWriteData etc as an option. However, with Swift I don't get these so I presume I'm doing something wrong.

Thanks in advance for any help.

Answer 1

I found it - the parameters were incorrect (totalBytesWritten: Int64! shouldn't have an ! at the end). The correct code is below:

func URLSession(session: NSURLSession, downloadTask: NSURLSessionDownloadTask, didWriteData bytesWritten: Int64, totalBytesWritten: Int64, totalBytesExpectedToWrite: Int64){

.....
}

Also, it's advisable to assign NSURLSessionDownloadDelegate to the containing class.