How to limit writable directory selection in NSOpenPanel?

Question

I want user to select a directory for files to save into. My simplest codes (ARC):

NSOpenPanel *panel = [NSOpenPanel openPanel];

[panel setCanChooseDirectories:YES];
[panel setCanChooseFiles:NO];
[panel setAllowsMultipleSelection:NO];

if (NSOKButton == [panel runModal]) 
    return [[panel URLs] objectAtIndex:0];
else
    return nil;

However, I want to ensure the returned path writeable so that I can save files into it. How should I modify my codes?

Answer 1

Implement the shouldEnableURL delegate method as follows:

- (BOOL)panel:(id)sender shouldEnableURL:(NSURL *)url
{
    return [[NSFileManager defaultManager] isWritableFileAtPath:[url path]];
}

This will render all non-writable paths as unselectable in the open panel. The object that acts as your panel delegate should conform to NSOpenSavePanelDelegate.
Don't forget to set it via:

[panel setDelegate:self];

Detailed information about the NSOpenSavePanelDelegate protocol can be found in the docs.

Answer 2

In Swift you can limit particular types this way, by implementing shouldEnable url delegate method.

 func panel(_ sender: Any, shouldEnable url: URL) -> Bool {
        if String(url.pathExtension) == "pdf" {
            return false
        }
        return true
 }