Open any folder with NSDocument

Question

I am trying to write an application that can open any folder in the NSDocument subclass but can't figure out the right Info.plist settings. It is important that my app should not use bundles, neither folders with a particular file extensions, just be able to open any folder.

What I tried:

• If I set the document type extension to empty string then the file open panel does not allow any file to be selected
• If I set the document type extension to * then the file open panel does enable all files but not the folders: folders are opened as in finder
• If I set the folder extension to the document type extension I can open the folder in the file open dialog as a document (this is what I want) but I restrict my solution to the folders with that extension
• By setting OSType to "fold", document type identifier or name to "public.folder" etc. as I read in regarding forums has no visible effect for me.

How can I open any folder in open file dialog?

Answer 1

For completeness here are some more details to @iKenndac's answer:

In IB check which method of First Responder is associated with the File / Open... menu item. In my case it was openDocument:. Implement this method in the AppDelegate:

-(void)openDocument:(id)sender
{
    NSOpenPanel *panel = [NSOpenPanel openPanel];
    [panel setCanChooseFiles:NO];
    [panel setCanChooseDirectories:YES];
    [panel setAllowsMultipleSelection:NO];

    [panel beginSheetModalForWindow:nil
                  completionHandler:^(NSInteger result) {
                      if (result == NSFileHandlingPanelOKButton) {
                          NSURL* selectedURL = [[panel URLs] objectAtIndex:0];
                          NSLog(@"selected URL: %@", selectedURL);
                          NSError* error = nil;
                          [[NSDocumentController sharedDocumentController] 
                              openDocumentWithContentsOfURL:selectedURL 
                                                   display:YES 
                                                     error:&error];
                      }
                  }];
}

You still need to define a Document Type in the Info.plist, setting the Identifier (LSItemContentTypes) field to public.folder.

Answer 2

You probably can't do this without writing some custom code.

You need to present an NSOpenPanel manually, like this:

NSOpenPanel *panel = [NSOpenPanel openPanel];
[panel setCanChooseFiles:NO];
[panel setCanChooseDirectories:YES];

[panel beginSheetForDirectory:nil
                         file:nil
               modalForWindow:[self window]
                modalDelegate:self
               didEndSelector:@selector(openPanelDidEnd:returnCode:contextInfo:)
                  contextInfo:nil];

An open panel presented in this way will let the use choose any directory they wish. You can implement NSOpenPanel's delegate methods to validate each folder and en/disable if if you need to.

Answer 3

Just as an updated summary of how one does that today, here's a step-by-step guide of what I had to do:

1. Create an application project from the Cocoa Application template using Xcode.

2. Check Create Document-based Application and leave whatever it suggests there for the "Document Extension" (it will refuse to enable the "Next" button if you delete the filename extension it right here, so we'll do that later).

3. Click your project's icon, go to the Info tab and to Document Types.

4. Delete the contents of the Extensions field. Our folders don't need a particular filename suffix

5. Write public.folder into the Identifier field.

6. Under Additional document type properties in the CFBundleTypeOSTypes array add one entry, fold (just those four lowercase letters). Not sure if that is necessary, but it's at least correct.

7. Make sure document is distributed as a bundle is not checked.

8. Create an NSDocumentController subclass containing the following method to your project. Name it E.g. ULIFolderDocumentController.

    -(void)openDocument:(id)sender
    {
        NSOpenPanel *panel = [NSOpenPanel openPanel];
        [panel setCanChooseFiles:NO];
        [panel setCanChooseDirectories:YES];
        [panel setAllowsMultipleSelection:NO];

        [panel beginWithCompletionHandler: ^( NSInteger result )
        {
            if (result == NSFileHandlingPanelOKButton)
            {
                NSURL* selectedURL = [[panel URLs] objectAtIndex:0];
                NSLog(@"selected URL: %@", selectedURL);
                [self openDocumentWithContentsOfURL: selectedURL
                        display: YES
                        completionHandler: ^(NSDocument * _Nullable document, BOOL documentWasAlreadyOpen, NSError * _Nullable error)
                        {
                            NSLog(@"%spened document %@ (%@)", (documentWasAlreadyOpen? "Reo" : "O"), document, error);
                        }];
            }
        }];
    }

9. Add a line to your app delegate's -init method that loads your subclass instead of NSDocumentController. This is easy, just request the shared object:

    [ULIFolderDocumentController sharedDocumentController]; // Override system's NSDocumentController with ours.

10. Try it! :)