UIImageView shows image on simulator but not on iPhone - objective-c

Question

I've been getting a very weird bug with one of my UIImageViews. I have a UITableView that lists items, and each cell is an item. Each item cell has a thumbnail image, a title, and a subtitle. I am able to show the thumbnail in every cell perfectly fine on the simulator and on the iPhone.
I also have a detail VC that, when a certain cell gets tapped, it segue's to that VC and shows the large image, along with some more info about the item. I've been able to load the image up in the simulator, but on the iPhone, all I get is a blank UIImageView.
This is how it looks in the simulator.
And my detail VC:
The blue view at the bottom is where I will add labels to show more details about the item, and the orange is a UIImageView that will show a custom image just saying 'item details'. One can tap on that, or my big UImageView and it will animate up (and down to dismiss).
Now, the problem is - when I segue from my table VC to my detail VC, the UIImageView is just blank on the iPhone. It works perfectly fine on the simulator, though, so I'm passing the right image and such.
Here is the code to segue:
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
if ([segue.identifier isEqualToString:#"showItemDetails"]) {
NSIndexPath *indexPath = [self.tableView indexPathForSelectedRow];
ItemDetailViewController *itemDetailVC = segue.destinationViewController;
Item *item = [self.fetchedResultsController objectAtIndexPath:indexPath];
if(item)
{
itemDetailVC.pictureImage = [UIImage imageWithContentsOfFile:item.photoURL];
}
}
}
My items gets saved using Core Data. photoURL is the URL of the photo in the documents directory of my app, as I do not save the entire image to Core Data, just a reference to it for performance purposes.
Here is part of the code that gets data from another VC in an "unwind" segue.
- (IBAction)saveItem:(UIStoryboardSegue *)segue
{
ManageItemViewController *manageItemVC = (ManageItemViewController *)segue.sourceViewController;
NSMutableDictionary *itemInfo = [[NSMutableDictionary alloc] init];
...
// write the original photo to a file and keep an URL to it that we pass to Core Data
NSData *imageData = [NSData dataWithData:UIImagePNGRepresentation(manageItemVC.pictureImage)];
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsPath = [paths objectAtIndex:0]; //Get the docs directory
NSString *fileName = [NSString stringWithFormat:#"%lf.png", [[NSDate date] timeIntervalSince1970]];
NSString *filePath = [documentsPath stringByAppendingPathComponent:fileName]; //Add the file name
[imageData writeToFile:filePath atomically:YES]; //Write the file
[itemInfo setObject:filePath forKey:CD_ITEM_PHOTOURL_PROPERTY];
...
[self saveItemToCoreData:[itemInfo copy]];
}
In my detail VC, this is all I do to load the UIImage I send to the big UIImageView.
- (void)viewWillAppear:(BOOL)animated
{
[super viewWillAppear:animated];
if(self.pictureImage) {
[self.pictureImageView setImage:self.pictureImage];
}
}
And when the user delete an item (delete row), I also remove the file from my documents directory, as such (this code is in my table VC):
- (void)deleteItemImageFromDevice:(NSString *)filePath
{
if(filePath)
{
NSFileManager *fileManager = [NSFileManager defaultManager];
NSError *error;
if([fileManager removeItemAtPath:filePath error:&error]) {
NSLog(#"Image deleted from documents directory!");
} else {
NSLog(#"%#", error);
}
}
}
I logged this and I do not get any errors in the simulator.
Anyone know what the issue is here? Thanks.

Answer 1

I've managed to fix this issue.
For future reference, here are the fixes I made to my code.
Instead of a time interval, I now get a guaranteed unique string (no need for long float conversions) using NSProcessInfo, as so:
NSString *fileName = [NSString stringWithFormat:#"%#.png", [[NSProcessInfo processInfo] globallyUniqueString]];
Then, in my prepareForSegue: method, I get an UIImage from data that exists in our documents folder (a file). The item.photoURL is our file path.
Item *item = [self.fetchedResultsController objectAtIndexPath:indexPath];
if(item.photoURL)
{
itemDetailVC.pictureImage = [UIImage imageWithData:[NSData dataWithContentsOfFile:item.photoURL]];
}
Lastly, in our detail VC header file, our UIImage (not UIImageView!) needs to be strong reference, not a weak one, as we need to access it even before the VC is on screen:
#property (nonatomic, strong) UIImage *pictureImage;
The UIImageView we assign this UIImage to can be weak because it only needs to be shown when the view is on screen, and that holds a strong pointer to all of its subviews. For an excellent analogy of strong vs weak, check this.