Save / Write NSMutableArray of objects to disk?

Question

Initially I thought this was going to work, but now I understand it won\'t because artistCollection is an NSMutableArray of \"Artist\" objects.

@interface Ar         


        

Answer 1

writeToFile:atomically: in Cocoa's collection classes only works for property lists, i.e. only for collections that contain standard objects like NSString, NSNumber, other collections, etc.

To elaborate on jdelStrother's answer, you can archive collections using NSKeyedArchiver if all objects the collection contains can archive themselves. To implement this for your custom class, make it conform to the NSCoding protocol:

@interface Artist : NSObject <NSCoding> {
    NSString *firName;
    NSString *surName;
}

@end


@implementation Artist

static NSString *FirstNameArchiveKey = @"firstName";
static NSString *LastNameArchiveKey = @"lastName";

- (id)initWithCoder:(NSCoder *)decoder {
    self = [super init];
    if (self != nil) {
        firName = [[decoder decodeObjectForKey:FirstNameArchiveKey] retain];
        surName = [[decoder decodeObjectForKey:LastNameArchiveKey] retain];
    }
    return self;
}   

- (void)encodeWithCoder:(NSCoder *)encoder {
    [encoder encodeObject:firName forKey:FirstNameArchiveKey];
    [encoder encodeObject:surName forKey:LastNameArchiveKey];
}

@end

With this, you can encode the collection:

NSData* artistData = [NSKeyedArchiver archivedDataWithRootObject:artistCollection];
[artistData writeToFile: @"/Users/Fgx/Desktop/stuff" atomically:YES];

Answer 2

Take a look at NSKeyedArchiver. Briefly :

NSData* artistData = [NSKeyedArchiver archivedDataWithRootObject:artistCollection];
[artistData writeToFile: @"/Users/Fgx/Desktop/stuff" atomically:YES];

You'll need to implement encodeWithCoder: on your Artist class - see Apple's docs

Unarchiving (see NSKeyedUnarchiver) is left as an exercise for the reader :)