Can I use NSUserDefaults to save the app’s table cell values? - ios

Question

I have a table which is populated by a title and image entry. This is done by the following methods:
tablePhotoViewController.m
- (IBAction)takePicture:(UIBarButtonItem *)sender {
// check #1 - make sure our source type is supported
if ([UIImagePickerController isSourceTypeAvailable:UIImagePickerControllerSourceTypeCamera]) {
NSArray *mediaTypes = [UIImagePickerController availableMediaTypesForSourceType:UIImagePickerControllerSourceTypeCamera];
// check #2 see if media type includes images
if ([mediaTypes containsObject:(NSString *)kUTTypeImage]) {
// create our image picker
UIImagePickerController *picker = [[UIImagePickerController alloc] init];
picker.delegate = self;
picker.sourceType = UIImagePickerControllerSourceTypeCamera;
picker.mediaTypes = [NSArray arrayWithObject:(NSString *)kUTTypeImage];
picker.allowsEditing = YES;
[self presentViewController:picker animated:YES completion:nil];
}
}
}
- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info
{
// do something with this image
UIImage *imagefromcamerabutton = [info objectForKey:UIImagePickerControllerEditedImage];
// handle the case where editting was not allowed...
if (!imagefromcamerabutton) imagefromcamerabutton = [info objectForKey:UIImagePickerControllerOriginalImage];
// save to photo albumn
ALAssetsLibrary *al = [Utils defaultAssetsLibrary];
[al writeImageToSavedPhotosAlbum:[imagefromcamerabutton CGImage] metadata:nil
completionBlock:^(NSURL *assetURL, NSError *error)
{
// once we know it's saved, grab the ALAsset and store
// it in our collection for display later
ALAssetsLibraryAssetForURLResultBlock resultblock = ^(ALAsset *myasset)
{
[self.photos addObject:myasset];
[self.tableView reloadData];
};
ALAssetsLibrary *assetslibrary = [Utils defaultAssetsLibrary];
[assetslibrary assetForURL:assetURL
resultBlock:resultblock
failureBlock:nil];
}];
[self dismissImagePicker];
}
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
return [self.photos count];
}
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *CellIdentifier = #"Cell";
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier forIndexPath:indexPath];
// Configure the cell...
ALAsset *asset = [self.photos objectAtIndex:indexPath.row];
[cell.imageView setImage:[UIImage imageWithCGImage:[asset thumbnail]]];
[cell.textLabel setText:[NSString stringWithFormat:#"Thing %d", indexPath.row+1]];
return cell;
}
This works well, but the problem is that after the user closes the app, the cell data is erased. I would like these to be able to stay as photos which are continually associated with the table unless the user taps a button to delete it from the array. From my limited understanding of how this could be done it looks like i need to somehow implement NSUserDefaults is that right or is there a better practice to achieve this goal?

Answer 1

NSUserDefaults is loaded completely into memory when it is accessed. This means if you data source contains more than a few items this would be really slow or it could even crash when the phone runs out of memory.
But, when I understand you code correctly you are storing the photos in the camera roll. Therefore you have some kind of URL to the image already (the assetURL in your code).
For a quick and kind of dirty solution (which I find OK for small amounts of data which does not change often, I use NSCoding. So you can add the title and the assetURL into a NSDictionary and add the dictionary to the array of your data source. Then in dealloc call
[NSKeyedArchiver archiveRootObject:self.myDataSourceArray toFile:[self pathToFileInDocumentsDirectory]];
In viewDidLoad you can then get the data back you call:
self.myDataSourceArray = [NSKeyedUnarchiver unarchiveObjectWithFile:[self pathToFileInDocumentsDirectory]];
If the data contains many items or the items are about to change much I tend to use Core Data or Sqlite. How to use those doesn't fit into this answer.