Question

I want to add NSCoding support to an c array of structs. Specifically this is for a subclass of MKPolyline, i.e. this is what I have to work with:

@property (nonatomic, readonly) MKMapPoint *points;
@property (nonatomic, readonly) NSUInteger pointCount;

+ (MKPolyline *)polylineWithPoints:(MKMapPoint *)points count:(NSUInteger)count;

I found a good answer on how to encode a individual struct. E.g.

NSValue* point = [NSValue value:&aPoint withObjCType:@encode(MKMapPoint)];
[aCoder encodeObject:point forKey:@"point"];

.... 

NSValue* point = [aDecoder decodeObjectForKey:@"point"];
[endCoordinateValue getValue:&aPoint];

Is there a nice way to apply this to a c Array – or will I simply have to iterate over the c-array?

Answer 1

Note: This approach only works if the data isn’t going between processors with different “endian-ness”. It should be safe going from iOS to iOS, certainly if only used on a given device.

You should be able to load the memory for the C-array into an NSData object then encode the NSData object.

MKMapPoint *points = self.points;
NSData *pointData = [NSData dataWithBytes:points length:self.pointCount * sizeof(MKMapPoint)];
[aCoder encodeObject:pointData forKey:@"points"];

Update: to get the data back:

NSData *pointData = [aCode decodeObjectForKey:@"points"];
MKMapPoint *points = malloc(pointData.length);
memcpy([pointData bytes], points);
self.points = points;