How to export package files in document based application on OSX? - objective-c

Question

in my app, I want to load certain image user picks, make some modification, after that, save a copy in my own file format. Since I want to keep track of user modification, I decided to export my file as a package(bundle).
So, in my document class, there's a NSImage object that holds the image file. In the fileWrapperOfType:error: method, I've setup a NSFileWrapper object, and put the object in it. Here's the code:
NSDictionary *fileWrappers = [self.documentFileWrapper fileWrappers];
if (image != nil) {
NSBitmapImageRep *imageRep = [image bitmapImageRepresentation];
NSData *imageData = [imageRep representationUsingType:NSPNGFileType properties:nil];
NSFileWrapper *imageFileWrapper = [[NSFileWrapper alloc]
initRegularFileWithContents:imageData];
[imageFileWrapper setPreferredFilename:#"image"];
[[self documentFileWrapper] addFileWrapper:imageFileWrapper];
}
return self.documentFileWrapper;
In my project plist file, I have two document types, first is the type of public.image since I need to load images in my app:
The other one is my own document type. To make the file a package, I've checked the bundle checkbox in xcode:
If I simply run this now, the code compains that finding extension from type identifier is deprecated, so, I managed to add an entry in Exported UTIs:
At this moment, everything seems working, except that the outputed folder with mdc extension, is indeed a folder instead of a package, what am I missing here? Thanks in advance!

Answer 1

Finally I solved the problem, the key here is to change Conforms To field to com.apple.package.

Answer 2

In order for a package on OS X to be a pkg, it must have a .pkg extension. I hope it is as simple as having the wrong extension.
Note: Until recently, .pkg files were merely directories. Now, we often see package.pkg packages that are obscured cannot be browsed causually without some tricks like using Pacifist, pkgutil or xar:
pkgutil --extract file.pkg folder/
or
xar -xf file.pkg