Question

Good evening everyone, I was hoping you could help with an Objective-C question I have.

In my app, I have a mutable array that contains 16 objects; the objects being images.

I would like to save and load the array so that the images are retained when the user quits the program.

I am new to data persistence and I can see there are several ways of saving and loading data and I am familiar with the NSUserDefaults method of saving and loading data. I am aware though that you cannot save arrays with images in this way.

Could someone please explain, perhaps with an example of the best and simplest way of saving and loading an array with images? Any help would be great as I’m unsure the best way to go with this.

Thanks everyone in advance!

Answer 1

Consider using NSKeyedArchiver.

// Archive
NSData *data = [NSKeyedArchiver archivedDataWithRootObject:theArray];
NSString *path = @"/Users/Anne/Desktop/archive.dat";
[data writeToFile:path options:NSDataWritingAtomic error:nil];

// Unarchive
NSString *path = @"/Users/Anne/Desktop/archive.dat";
NSMutableArray *theArray = [NSKeyedUnarchiver unarchiveObjectWithFile:path];

This way you can be sure the unarchived array is identical to the original.
All classes conforming to the NSCoding protocol can be used by NSKeyedArchiver.

Note: You can use any extension.

Response to comment:

The following should work on iOS:

// The Array
NSMutableArray * array = [[NSMutableArray alloc] init]; 

// Determine Path
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *path = [ [paths objectAtIndex:0] stringByAppendingPathComponent:@"archive.dat"];

// Archive Array
NSData *data = [NSKeyedArchiver archivedDataWithRootObject:array];
[data writeToFile:path options:NSDataWritingAtomic error:nil];

// Unarchive Array
NSMutableArray *theArray = [NSKeyedUnarchiver unarchiveObjectWithFile:path];