Correct way to save/serialize custom objects in iOS

My implementation for something similar is the following and works perfectly :

The custom object (Settings) should implement the protocol NSCoding :

-(void)encodeWithCoder:(NSCoder *)encoder{
    [encoder encodeObject:self.difficulty forKey:@"difficulty"];
    [encoder encodeObject:self.language forKey:@"language"];
    [encoder encodeObject:self.category forKey:@"category"];
    [encoder encodeObject:self.playerType forKey:@"playerType"];
}

- (id)initWithCoder:(NSCoder *)decoder {
    if (self = [super init]) {
        self.difficulty = [decoder decodeObjectForKey:@"difficulty"];
        self.language = [decoder decodeObjectForKey:@"language"];
        self.category = [decoder decodeObjectForKey:@"category"];
        self.playerType = [decoder decodeObjectForKey:@"playerType"];
    }
    return self;
}

The following code writes the custom object to a file (set.txt) and then restores it to the array myArray :

NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
NSString *appFile = [documentsDirectory stringByAppendingPathComponent:@"set.txt"];

NSMutableArray *myObject=[NSMutableArray array];
[myObject addObject:self.settings];    

[NSKeyedArchiver archiveRootObject:myObject toFile:appFile]; 

NSMutableArray* myArray = [NSKeyedUnarchiver unarchiveObjectWithFile:appFile];