Decoding CBUUID Data into NSString in iOS CoreBluetooth [duplicate] - ios

Question

I can't find any official way to get a UUID string back out of a CBUUID. These UUIDs can be 2 or 16 bytes long.
The goal is to store CBUUIDs in a file somewhere as a string, and then resurrect with [CBUUID UUIDWithString:] etc. Here is what I have so far.
// returns a simple 4 byte string for 16bit uuids, 128 bit uuids are in standard 8-4-4-4-12 format
// the resulting string can be passed into [CBUUID UUIDWithString:]
+(NSString*)CBUUIDToString:(CBUUID*)cbuuid;
{
NSData* data = cbuuid.data;
if ([data length] == 2)
{
const unsigned char *tokenBytes = [data bytes];
return [NSString stringWithFormat:#"%02x%02x", tokenBytes[0], tokenBytes[1]];
}
else if ([data length] == 16)
{
NSUUID* nsuuid = [[NSUUID alloc] initWithUUIDBytes:[data bytes]];
return [nsuuid UUIDString];
}
return [cbuuid description]; // an error?
}

Answer 1

I rigged up the following category to do this for CBUUID:
#interface CBUUID (StringExtraction)
- (NSString *)representativeString;
#end
#implementation CBUUID (StringExtraction)
- (NSString *)representativeString;
{
NSData *data = [self data];
NSUInteger bytesToConvert = [data length];
const unsigned char *uuidBytes = [data bytes];
NSMutableString *outputString = [NSMutableString stringWithCapacity:16];
for (NSUInteger currentByteIndex = 0; currentByteIndex < bytesToConvert; currentByteIndex++)
{
switch (currentByteIndex)
{
case 3:
case 5:
case 7:
case 9:[outputString appendFormat:#"%02x-", uuidBytes[currentByteIndex]]; break;
default:[outputString appendFormat:#"%02x", uuidBytes[currentByteIndex]];
}
}
return outputString;
}
#end
For this input:
NSLog(#"UUID string: %#", [[CBUUID UUIDWithString:#"0bd51666-e7cb-469b-8e4d-2742f1ba77cc"] representativeString]);
NSLog(#"UUID string2: %#", [[CBUUID UUIDWithString:#"1800"] representativeString]);
it produces the following output:
UUID string: 0bd51666-e7cb-469b-8e4d-2742f1ba77cc
UUID string2: 1800
and preserves the appropriate hyphenation for the 16 byte UUIDs, while supporting the simple 2-byte UUIDs.

Answer 2

To all those saying that CBUUID is toll-free bridged with CFUUIDRef, it's not.
CBUUID * foo = [CBUUID UUIDWithString:CBUUIDCharacteristicExtendedPropertiesString];
CFStringRef fooBar = CFUUIDCreateString(NULL, (__bridge CFUUIDRef)foo);
if (![CBUUIDCharacteristicExtendedPropertiesString isEqualToString:(__bridge NSString *)fooBar])
NSLog(#"fubar!");
It's not crashing but you're getting garbage out. It's probably uniquely identifying garbage, but it can't be round-tripped.
PS: This didn't work as a comment because SO comments oddly don't allow code formatting.

Answer 3

iOS 7.1 (beta released yesterday, 11/18/13) introduced the following property on CBUUID:
#property(nonatomic, readonly) NSString *UUIDString
The UUID represented as a string. (read-only)
From CBUUID Class Reference.
It's also worth noting that for comparing a UUID string with a CBUUID, this works:
if ([cbuuidInQuestion isEqual:[CBUUID UUIDWithString:#"1234-5678-9012-1234"]]) {
// isEqual tests for "the same UUID"
// == tests for "the same CBUUID object"
}

Answer 4

I know it's been 7 month since it was asked and answered, but... CBUUID is “toll-free bridged” to CFUUID and the easiest way to convert is
//CBUUID* uuid = descr.UUID;
NSString* str = CFUUIDCreateString(nil, uuid);

Answer 5

Here is swift extension of Brad Larson's answer :
import CoreBluetooth
extension CBUUID {
func representativeString() -> String {
let data = self.data
let bytesToConvert = data.length
let uuidBytes = UnsafePointer<CUnsignedChar>(data.bytes)
var outputString = String()
for currentByteIndex in 0..<bytesToConvert {
switch currentByteIndex {
case 3,5,7,9:
outputString += String(format: "%02x-",uuidBytes[currentByteIndex])
default:
outputString += String(format: "%02x",uuidBytes[currentByteIndex])
}
}
return outputString
}
}
From iOS 7.1 UUIDString property is there but for specific iOS7, above extension is good option.

Answer 6

There is native method in objective C and Swift and it is quite straight forward method.
NSString *str = characteristic.UUID.UUIDstring;
Same thing with Swift language
Link to library->
https://developer.apple.com/documentation/corebluetooth/cbuuid/1518742-uuidstring?language=objc

Answer 7

Brad's answer does its work, but the solution could be simpler (though probably not more efficient) using NSUUID class:
// CBUUID+ToString.h
#import <CoreBluetooth/CoreBluetooth.h>
#interface CBUUID (ToString)
- (NSString *)toString;
#end
// CBUUID+ToString.m
#import "CBUUID+ToString.h"
#implementation CBUUID (ToString)
- (NSString *)toString {
if ([self respondsToSelector:#selector(UUIDString)]) {
return [self UUIDString]; // Available since iOS 7.1
} else {
return [[[NSUUID alloc] initWithUUIDBytes:[[self data] bytes]] UUIDString]; // iOS 6.0+
}
}
#end

Answer 8

The following Worked me without any error:
NSString *str = [[NSString alloc] initWithFormat:#"%#", CFUUIDCreateString(nil, peripheral.UUID) ];