Error of Unexpected class while encode/decode an NSArray with NSSecureCoding

NSCoder provides an additional method decodeObjectOfClasses:forKey:, where a set of expected objects could be passed. This allows to decode nested structures.

Just pass a set with the NSArray and your ClassA and ClassB class:

NSSet *classes = [NSSet setWithObjects:[NSArray class], [ClassA class] ,[ClassB class], nil];
NSArray* array = [unarchiver decodeObjectOfClasses:classes forKey:@"AirdropDataKey"];