How to convert NSValue to NSData and back?

Question

A have a number of NSValue (obtained via KVC valueForKey) that I need to append to an NSData object in order to send it over the netwo

Answer 1

Since NSValue adopts the NSCoding protocol, you can use the NSCoder subclasses, NSKeyedArchiver and NSKeyedUnarchiver:

- (NSData *)dataWithValue:(NSValue *)value {
  return [NSKeyedArchiver archivedDataWithRootObject:value];
}

- (NSValue *)valueWithData:(NSData *)data {
  return (NSValue *)[NSKeyedUnarchiver unarchiveObjectWithData:data];
}

If NSKeyedArchiver and NSKeyedUnarchiver can't be used (for resulting data size issues), then you would have to find the size of the contained value yourself:

- (NSData *)dataWithValue:(NSValue *)value {
  // Can use NSGetSizeAndAlignment() instead. See LearnCocos2D's answer.
  if (type[0] == '{') {
    // Use the various NSValue struct value methods to detect the type.
  } else if (type[0] == 'c') {
    size = sizeof(char);
  } else if (type[0] == 'i') {
    size = sizeof(int);     
  } // etc for all/most of the values in the table linked below [1];

  void *bytes = malloc(size);
  [value getValue:bytes];
  return [NSData dataWithBytes:bytes length:size];
}

[1]: Objective-C Type Encodings