NSURLConnectionDownloadDelegate file issue

问题

Now that 5.0 is launched and we can discuss it without breaching Apple's NDA, I have an issue with the new version of NSURLConnection. This has a new delegate, NSURLConnectionDownloadDelegate with two key methods.

1. connection:didWriteData:totalBytesWritten:expectedTotalBytes: is invoked repeatedly while the file download is progressing

2. connectionDidFinishDownloading:destinationURL: is called once when the download is complete.

The downloaded file should then be at destinationURL (at least for the life of this method - the intent is that you get it and move it somewhere permanent). The issue is : it's not there. That directory is empty. I have reported this as a bug to Apple and they tell me it is a duplicate of an issue that they are already aware of.

If anyone has a workaround for this, or finds they can use this delegate successfully, please let me know.

UPDATE 10/17/2011 : I've given up on this and gone back to the old delegate which still works fine in 5.0 even though the documentation says the delegate methods are only available thru 4.3.

回答1:

Apparently only for use with Newsstand apps. This guy might have found a work around:

http://adamernst.com/post/18948400652/a-replacement-for-nsurlconnectiondownloaddelegate

Alternatively, just use NSURLConnection. But heads up if you implement the NSURLDownloadDelegate methods, they appear to override the standard NSURLConnection delegate methods. If it's the handy didWriteData: method of NSURLConnectionDownloadDelegate that you want, e.g. to update a UIProgressView, you can achieve the same by grabbing the total file size from the http response, and by using the didReceiveData: method of NSURLConnection.

回答2:

Documentation tells the file is only guaranteed to exist while the delegate method is called so you will need to copy it somewhere else the moment the delegate method is called.

Google tells me people are having problems when the Server sends a cryptic filename and/or mime-type.

回答3:

Folks,

I've recently discovered this new NSURLConnectionDataDelegate protocol. However, the iOS 5 documentation is incomplete.

The New NSURLConnectionDataDelegate protocol is in the documentation, but the new version of NSURLConnection that uses it is not. That documentation still tells us to use the now deprecated NSURLConnectionDelegate protocol methods.

I gather that NSURLConnection will now download data from a remote URL directly to a file on the local disk, much like the NSURLDownload class in Mac OS. How do I figure out how this works?

The header for NSURLConnection hints that the connection object deduces what you want based on which version of the NSURLConnectionDelegate protocol the delegate conforms to. That seems really screwy. I've never heard of using the protocol conformity of a delegate as a way of controlling the behavior of a class before.

回答4:

Even now NSURLConnectionDownloadDelegate doens't work.

Here is a good replacement: http://github.com/jbrennan/JBContainedURLConnection

来源：https://stackoverflow.com/questions/7754470/nsurlconnectiondownloaddelegate-file-issue