Saved photos don't appear on device after update - ios

Question

On my iPhone app, I'm saving pictures associated with an event via this code:
[pngData writeToFile:filePath atomically:YES]; //Write the file
self.thisTransaction.picPath = filePath;
Later I retrieve and display the photo with this code:
UIImage * image = [UIImage imageWithContentsOfFile:thisTransaction.picPath];
Works great on my iPad (I don't have an iPhone).
However, if I update the app by connecting the iPad to my MB Pro after an Xcode code modification not involving the above lines, then disconnect and run it independently, the picture at the expected picPath is not retrieved. All other data associated with thisTransaction in Core Data is intact and unchanged, but the expected picture doesn't appear on the device after the update.
Can someone please tell me where I'm going wrong?
Edit to clarify file path construction
pngData = UIImagePNGRepresentation(capturedImage.scaledImage);
NSLog(#"1 The size of pngData should be %lu",(unsigned long)pngData.length);
//Save the image someplace, and add the path to this transaction's picPath attribute
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsPath = [paths objectAtIndex:0]; //Get the docs directory
int timestamp = [[NSDate date] timeIntervalSince1970];
NSString *timeTag = [NSString stringWithFormat:#"%d",timestamp];
filePath = [documentsPath stringByAppendingPathComponent:timeTag]; //Add the file name
NSLog(#"1 The picture was saved at %#",filePath);
The console log shows this filePath:
/Users/YoursTruly/Library/Developer/CoreSimulator/Devices/65FB33E1-03A7-430D-894D-0C1893E03120/data/Containers/Data/Application/EB9B9523-003E-4613-8C34-4E91B3357F5A/Documents/1433624434

Answer 1

The issue you are having is that the location of an app's sandbox can change over time. Typically this happens when an app is updated. So the worst thing you can do is persist absolute file paths.
What you need to do is persist just the part of the path relative to the base path (the "Documents" folder in this case).
Then when you want to reload the file again, append the persisted relative path to the current value of the "Documents" folder.
So your code needs to be something like this:
Save the file:
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsPath = [paths objectAtIndex:0]; //Get the docs directory
int timestamp = [[NSDate date] timeIntervalSince1970];
NSString *timeTag = [NSString stringWithFormat:#"%d",timestamp];
filePath = [documentsPath stringByAppendingPathComponent:timeTag]; //Add the file name
[pngData writeToFile:filePath atomically:YES]; //Write the file
self.thisTransaction.picPath = timeTag; // not filePath
Load the file:
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsPath = [paths objectAtIndex:0]; //Get the docs directory
NSString *filePath = [documentsPath stringByAppendingPathComponent:thisTransaction.picPath];
UIImage *image = [UIImage imageWithContentsOfFile:filePath];