Question

Right now on my iPhone application I’m saving a large chunk of data from a NSData object to NSUserDefaults. I know that’s not the best approach because NSUserDefaults is meant only to store small pieces of data.

I’m doing this something like this:

NSData *data = [NSData alloc]init]];
[[NSUserDefaults standardUserDefaults] setObject:data forKey:@"MyData"];

For late retrieval of this data.

What’s the correct way to save this data permanently for further use?

Answer 1

Make a custom class with the properties you want (.h file):

#import <Foundation/Foundation.h>

@interface CustomHolder : NSObject {
    NData *data;
}

@property (strong, nonatomic) NSData *data;

@end

And then set the .m file up so that you can encode/decode the object

#import "CustomHolder.h"

@implementation CustomHolder

@synthesize data;

- (void)encodeWithCoder:(NSCoder *)encoder 
{
    [encoder encodeObject:data forKey:@"data"];
}

- (id)initWithCoder:(NSCoder *)decoder 
{
    if (self = [super init]) 
    {
        self.data = [decoder decodeObjectForKey:@"data"]; 
    }
    return self;
}

@end

Then you can just [NSKeyedArchiver archiveRootObject:obj toFile:[self saveFilePath]] to save and [NSKeyedUnarchiver unarchiveObjectWithFile:[self saveFilePath]] to load.

This works for any kind of data, and gives you the option of adding as many different data files as you need to an object.