iOS: Can't save file to 'Application Support' folder, but can to 'Documents'

Question

I can download and save a binary file to the 'Documents' folder with a custom name perfectly fine.

If I just change the URL to the 'Application Support' folder instead of the 'Documents' folder, it fails to write to that URL saying it doesn't exist.

Here's the URL construction code:

- ( NSURL * ) getSaveFolder
{
    NSURL * appSupportDir    = nil;
    NSURL * appDirectory     = nil;
    NSArray * possibleURLs   = [[NSFileManager defaultManager] URLsForDirectory:NSApplicationSupportDirectory inDomains:NSAllDomainsMask];
    
    if ( [possibleURLs count] >= 1 )
    {
        appSupportDir = [possibleURLs objectAtIndex:0];
    }

    if ( appSupportDir != nil)
    {
        NSString * appBundleID = [[NSBundle mainBundle] bundleIdentifier];
        appDirectory           = [appSupportDir URLByAppendingPathComponent:appBundleID];
    }

    return appSupportDir;
}

Here's the saving code:

- ( void ) writeOutDataToFile:( NSData * )data
{
    NSURL * finalURL = [self.rootPathURL URLByAppendingPathComponent:self.aFileName];

    [data writeToURL:finalURL atomically:YES];
}

---

If I change the NSArray to:

NSArray * possibleURLs   = [[NSFileManager defaultManager] URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask];

then it saves fine.

I've read the Apple Docs on File stuff and can't fix this - what am I missing?

Answer 1

Unlike the Documents directory, the Application Support directory does not exist in the app's sandbox by default. You need to create it before you can use it.

And a much simpler way to get a reference to the directory is:

NSArray *paths = NSSearchPathForDirectoriesInDomains(NSApplicationSupportDirectory, NSUserDomainMask, YES);
NSString *appSupportDirectory = paths.firstObject;