NSJSONSerialization and Emoji - ios

Question

I'm currently trying to POST some JSON containing emojis to a python API. I tried feeding the NSJSONSerialization directly with the string containing the emojis from my UITextField but the serializer crashed with no meaningful explanation.
Afterwards I tried to do some format conversion and ended up with something like this:
NSString *uniText = mytextField.text;
NSData *msgData = [uniText dataUsingEncoding:NSNonLossyASCIIStringEncoding];
NSString *goodMsg = [[NSString alloc] initWithData:msgData encoding:NSUTF8StringEncoding] ;
This basically works except that the resulting UTF-8 is kinda double-"escaped" resulting in the following:
"title":"\\ud83d\\udc8f\\ud83d\\udc8f\\ud83d\\udc8f\\ud83d"
Any suggestions how to fix that?

Answer 1

There are two difficulties:
1. Apple hosed NSString WRT UTF Planes 1 and above, the underlying use
of UTF-16 shows through. An example is that length will return 2 for
one emoji character.
2. Whoever decided to put emoji in Plane 1 was
just being difficult, it is the first use of Plane 1 and a lot of
legacy UTF code does not handle that correctly.
Example code (adapted from #Hot Licks):
Updated with OP emoji
NSString *uniText = #"💦💏👒👒💦";
NSDictionary* jsonDict = #{#"title":uniText};
NSData * utf32Data = [uniText dataUsingEncoding:NSUTF32LittleEndianStringEncoding];
NSLog(#"utf32Data: %#", utf32Data);
NSError* error = nil;
NSData* jsonData = [NSJSONSerialization dataWithJSONObject:jsonDict options:0 error:&error];
if (jsonData == nil) {
NSLog(#"JSON serialization error: %#", error);
}
else {
NSString* jsonString = [[NSString alloc] initWithData:jsonData encoding:NSUTF8StringEncoding];
NSLog(#"The JSON result is %#", jsonString);
NSLog(#"jsonData: %#", jsonData);
}
NSLog output
utf32Data: a6f40100 8ff40100 52f40100 52f40100 a6f40100
The JSON result is {"title":"💦💏👒👒💦"}
jsonData: 7b227469 746c6522 3a22f09f 92a6f09f 928ff09f 9192f09f 9192f09f 92a6227d

Answer 2

Sigh:
NSString* uniText = mytextField.text;
NSDictionary* jsonDict = #{#"title":uniText};
NSError* error = nil;
NSData* jsonData = [NSJSONSerialization dataWithJsonObject:jsonDict options:0 error:&error];
if (jsonData == nil) {
NSLog(#"JSON serialization error: %#", error);
}
else {
NSString* jsonString = [[NSString alloc] initWithData:jsonData encoding:NSUTF8StringEncoding];
NSLog(#"The JSON result is %#", jsonString);
}
If myTextField.text is a valid NSString then no other conversions should be required. NSJSONSerialization will provide all necessary "escaping".