Writing/loading to/from file - ios

Question

Im trying to learn how to save/load images, and i just don't get why this wont work. Im writing a screenshot to the filesystem like this:
if ([[UIScreen mainScreen] respondsToSelector:#selector(scale)])
UIGraphicsBeginImageContextWithOptions(self.view.bounds.size, NO, [UIScreen mainScreen].scale);
else
UIGraphicsBeginImageContext(self.view.bounds.size);
[self.view.layer renderInContext:UIGraphicsGetCurrentContext()];
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
NSData * data = UIImagePNGRepresentation(image);
NSArray *directories = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [directories objectAtIndex:0];
NSString *key = [documentsDirectory stringByAppendingPathComponent:#"screenshots.archive"];
[data writeToFile:key atomically:YES];
And in the "init" medthod in my UITableView subclass, i do this:
pics = [[NSMutableDictionary alloc]initWithContentsOfFile:[self dataFilePath]];
dataFilePath method:
- (NSString *)dataFilePath
{
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
return [documentsDirectory stringByAppendingPathComponent:#"screenshots.archive"];
}
To test if this works i have this delegate method:
-(NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section{
return pics.count;
}
I test it by taking a screenshot, and then initializing my UITableview subclass, but it show no rows. What am i doing wrong?

Answer 1

There are a few key issues with the code that are causing it to not work. You're storing the image data directly to the file and trying to read it back as a dictionary. You'll want to wrap the image in an array first, and write the array to the file. Then you'll want to read the file into an array for the table to display. To sum up the changes:
Change
[data writeToFile:key atomically:YES];
to
NSMutableArray *storageArray = [NSMutableArray arrayWithContentsOfFile:key];
if(!storageArray)
storageArray = [NSMutableArray arrayWithObject:data];
else
[storageArray addObject:data];
[storageArray writeToFile:key atomically:YES];
and change
pics = [[NSMutableDictionary alloc]initWithContentsOfFile:[self dataFilePath]];
to
pics = [[NSArray alloc] initWithContentsOfFile:[self dataFilePath]];