How to pass NSData as NSString and get it back? - iphone

Question

i have a NSData object.
I want to convert it to a string, pass to a function and then reconvert back to NSData object.
But How?
I tried this method, but NSData value it's different from the original!
here my code:
// a generic class
APClass *c = [[APClass alloc] init];
c.aNumber = 123;
c.aString = #"my string";
// my data obj
NSMutableData *data = [NSMutableData data];
// archiver to store class in nsdata
NSKeyedArchiver *encoder = [[NSKeyedArchiver alloc] initForWritingWithMutableData:data];
[encoder encodeObject:[NSNumber numberWithInt:c.aNumber] forKey:#"aNum"];
[encoder encodeObject:c.aString forKey:#"aStr"];
[encoder finishEncoding];
[encoder release];
[c release];
NSLog(#"%#", data);
NSString *d = [NSString stringWithFormat:#"%#", data];
// ---
NSString *strFromData = [NSString stringWithFormat:#"%#", d];
NSData *dataNM = [strFromData dataUsingEncoding:NSUTF8StringEncoding];
// decoder to retrieve class from nsdata
NSKeyedUnarchiver *decoder = [[NSKeyedUnarchiver alloc] initForReadingWithData:dataNM];
int number = [[decoder decodeObjectForKey:#"aNum"] intValue];
NSString *string = [decoder decodeObjectForKey:#"aStr"];
[decoder finishDecoding];
[decoder release];
NSLog(#"[Number: %d] -- [String: %#]", number, string);
How can i convert back to original NSData?
data and dataNM are different in size.
Compiler give back this error:
2012-04-02 16:33:28.269 DataTest[18008:f803] -[__NSCFData
objectForKey:]: unrecognized selector sent to instance 0x6b46c80
2012-04-02 16:33:28.270 DataTest[18008:f803] * Terminating app due
to uncaught exception 'NSInvalidArgumentException', reason:
'-[__NSCFData objectForKey:]: unrecognized selector sent to instance
0x6b46c80'
thanks.

Answer 1

Solved.
Using dataUsingEncoding, value of NSData it's different.
To pass data around methods or apps, etc, i've used base64 convertion.
Encode
NSString *d =
[NSString stringWithFormat:#"appdue://obj=%#",
[APBase64Converter base64forData:data]];
Decode
NSData *data = [APBase64Converter base64DataFromString:urlParams];
APBase64Converter Is a lib that encode/decode easily data and strings.
Working example and APBase64Converter lib can be downloaded from here: http://goo.gl/8YNjS
Thanks all.
I "retain" this post for helps people and me next time!

Answer 2

Use
NSData to NSString:
- (id)initWithData:(NSData *)data encoding:(NSStringEncoding)encoding
and
NSString to NSData:
- (NSData *)dataUsingEncoding:(NSStringEncoding)encoding
with encoding
NSUTF8StringEncoding
or
NSMacOSRomanStringEncoding (which is an 8-bit encoding).

Answer 3

Use Base64 class it is available in github
DatabaseResult* result = [self.database executeQuery:#"SELECT * FROM `images` WHERE image_id = ? AND imagetype = ?", self.routeId,self.imagetype];
for(EGODatabaseRow* row in result) {
NSString *strImage=[row stringForColumn:#"image_photo"];
[Base64 initialize];
NSData *data = [Base64 decode:strImage];
UIImage *image=[UIImage imageWithData:data];
}
This is how i convert String to data and then data to image.