Use below code.

NSString* myString;
myString = [[NSString alloc] initWithData:nsdata encoding:NSASCIIStringEncoding];

-[NSString initWithData:encoding] will return nil if the specified encoding doesn't match the data's encoding.

Make sure your data is encoded in UTF-8 (or change NSUTF8StringEncoding to whatever encoding that's appropriate for the data).

The docs for NSString says

https://developer.apple.com/documentation/foundation/nsstring/1416374-initwithdata

Return Value An NSString object initialized by converting the bytes in data into Unicode characters using encoding. The returned object may be different from the original receiver. Returns nil if the initialization fails for some reason (for example if data does not represent valid data for encoding).

You should try other encoding to check if it solves your problem

 // The following constants are provided by NSString as possible string encodings.
enum {
NSASCIIStringEncoding = 1,
NSNEXTSTEPStringEncoding = 2,
NSJapaneseEUCStringEncoding = 3,
NSUTF8StringEncoding = 4,
NSISOLatin1StringEncoding = 5,
NSSymbolStringEncoding = 6,
NSNonLossyASCIIStringEncoding = 7,
NSShiftJISStringEncoding = 8,
NSISOLatin2StringEncoding = 9,
NSUnicodeStringEncoding = 10,
NSWindowsCP1251StringEncoding = 11,
NSWindowsCP1252StringEncoding = 12,
NSWindowsCP1253StringEncoding = 13,
NSWindowsCP1254StringEncoding = 14,
NSWindowsCP1250StringEncoding = 15,
NSISO2022JPStringEncoding = 21,
NSMacOSRomanStringEncoding = 30,
NSUTF16StringEncoding = NSUnicodeStringEncoding,
NSUTF16BigEndianStringEncoding = 0x90000100,
NSUTF16LittleEndianStringEncoding = 0x94000100,
NSUTF32StringEncoding = 0x8c000100,
NSUTF32BigEndianStringEncoding = 0x98000100,
NSUTF32LittleEndianStringEncoding = 0x9c000100,
NSProprietaryStringEncoding = 65536
};

-[NSString initWithData:encoding] is your friend but only when you use a proper encoding.

NSString *string = [NSString stringWithUTF8String:[Data bytes]];

Objective C:

[[NSString alloc] initWithData:nsdata encoding:NSASCIIStringEncoding];

Swift:

let str = String(data: data, encoding: .ascii)

in objective C:

NSData *tmpData;
NSString *tmpString = [NSString stringWithFormat:@"%@", tmpData];
NSLog(tmpString)

Swift:

let jsonString = String(data: jsonData, encoding: .ascii)

or .utf8 or whatever encoding appropriate

Unsure of data's encoding type? No problem!

Without need to know potential encoding types, in which wrong encoding types will give you nil/null, this should cover all your bases:

NSString *dataString = [data base64EncodedStringWithOptions:NSDataBase64EncodingEndLineWithCarriageReturn];

Done!

Note: In the event this somehow fails, you can unpack your NSData with NSKeyedUnarchiver , then repack the (id)unpacked again via NSKeyedArchiver, and that NSData form should be base64 encodeable.

id unpacked = [NSKeyedUnarchiver unarchiveObjectWithData:data];
data = [NSKeyedArchiver archivedDataWithRootObject:unpacked];

Objective C includes a built-in way to detect a the encoding of a string embedded in NSData.

NSData* data = // Assign your NSData object...


NSString* string;
NSStringEncoding encoding = [NSString stringEncodingForData:data encodingOptions:nil convertedString:&string usedLossyConversion:nil];