Error "[general] *** -[NSKeyedUnarchiver validateAllowedClass:forKey:] allowed unarchiving ..."

Question

I'm on macOS Monterey (12.0.1), not iOS, objective-c, XCode 13

I'm receiving this log message after building my app for arm64:

[general] *** -[NSKeyedUnarchiver validateAllowedClass:forKey:] allowed unarchiving safe plist type ''NSString' (0x1dcb1c848) [/System/Library/Frameworks/Foundation.framework]' for key 'NS.objects', even though it was not explicitly included in the client allowed classes set: '{(
    "'NSDictionary' (0x1dcaee5d0) [/System/Library/Frameworks/CoreFoundation.framework]"
)}'. This will be disallowed in the future.

Any idea what's causing this and how to get rid of it?

Edit: it seems to happen with every app compiled on arm64 starting with macOS Monterey. So it might be a generic apple bug

Answer 1

Thanks to @OI Sen it've had a closer look to the NSUnarchiver. First of all NSKeyedUnarchiver should be allocated and initialized like this:

NSError* err;

NSKeyedUnarchiver* unarchiver = [[NSKeyedUnarchiver alloc] initForReadingFromData:someData error:&err];

In my specific case I use NSSecure coding. Therefore you have to specify classes on decoding objects. In my case it looked like this

NSDictionary* someDict = [unarchiver decodeObjectOfClass:[NSDictionary class] forKey:NSKeyedArchiveRootObjectKey];

But the NSDictionary contained additional strings. That was the cause of the log message. By adding NSString to the decoded class list the error is gone.

NSDictionary* someDict = [unarchiver decodeObjectOfClasses:[[NSSet alloc] initWithArray:@[[NSDictionary class],[NSString class]]] forKey:NSKeyedArchiveRootObjectKey];

Answer 2

Another related situation is if you're using NSCoder.

This code generated the warning:

self.expression = [aDecoder decodeObjectForKey: kExpression];

Warning eliminated with:

self.expression = [aDecoder decodeObjectOfClass:[NSString class] forKey:kExpression];

Note use of decodeObjectOfClass:[NSString class] instead of decodeObjectForKey.