converting NSDictionary object to NSData object and vice-versa

Question

I have to convert an NSDictionary object into NSData and further I have to get the same NSDictionary out of the NSData object. How should I go about it?

Answer 1

use NSKeyedArchiver

To convert NSDictionary To NSData

NSMutableData *data = [[NSMutableData alloc]init];
NSKeyedArchiver *archiver = [[NSKeyedArchiver alloc]initForWritingWithMutableData:data];
[archiver encodeObject:YOURDICTIONARY forKey: YOURDATAKEY];
archiver finishEncoding];
[data writeToFile:YOURFILEPATH atomically:YES];
[data release];
[archiver release];

To get the NSDictionary back from the stored NSData

NSData *data = [[NSMutableData alloc]initWithContentsOfFile:YOURFILEPATH];
NSKeyedUnarchiver *unarchiver = [[NSKeyedUnarchiver alloc] initForReadingWithData:data];
YOURDICTIONARY = [unarchiver decodeObjectForKey: YOURDATAKEY];
[unarchiver finishDecoding];
[unarchiver release];
[data release];

Answer 2

A much simpler version of Robert's answer:

[NSKeyedArchiver archiveRootObject:YOURDICTIONARY toFile:YOURFILEPATH];

And, correspondingly:

YOURDICTIONARY = [NSKeyedUnarchiver unarchiveObjectWithFile:YOURFILEPATH];

Or to answer the question as originally set, without imputing a file into things:

NSData *data = [NSKeyedArchiver archivedDataWithRootObject:YOURDICTIONARY];
...
YOURDICTIONARY = [NSKeyedUnarchiver unarchiveObjectWithData:data];

It's all factory methods so it's the same code with or without ARC; the methods used have been available since OS X v10.2 and on iOS since day one.