iOS 4 bug? Image files saved to folder are overwritten after a random number of images saved - objective-c

Question

I have an APP (SDK 4.3) which saves images being attachmemnts for a waypoint on a google map.
The file save is pretty standard (afaik) UIImagePickerController code.
Rather than saving to the camera roll I was saving the image and then the thumbnail to a subfolder. I need that.
At seemingly random points with no errors being trapped at all and logged, the images will not save to the folder but instead over-write previously saved image files!
It looks for all the world like a FIFO pop going on.
It is seriously odd and I have even built a small test APP and fired it up as soon as the spookiness appeared...saving a series of camera images to the same folders but see the same effect. The images get over-written once the random magic file number is reached!
Random in the sense that after 7 saved images, the overwriting begins...even after a reboot of the phone to ensure memory leaks is not the issue. Wipe the APP and try again...
This time it will happen after 16 oR 23 image files saved.
I have gone to all sorts of extremes and cannot find the source of the issue.
In the small test APP, in the same method I save out to the camera roll as well. It will save there but overwrite in the folder. The file names are 10 character random generated alpha-numeric.
I am now leaning to understand this as a bug. I can always reproduce the error but not predictably. It arises randomly.
I would appreciate help as I am tearing my hair out.
Here is the code...
//tester.h
#import <UIKit/UIKit.h>
#interface tester : UIViewController <UINavigationControllerDelegate, UIImagePickerControllerDelegate>
{
UIImagePickerController *imgPicker;
IBOutlet UIButton *pressit;
IBOutlet UIButton *seeya;
UIActivityIndicatorView *activity;
}
#property (retain )UIImagePickerController *imgPicker;
#property (nonatomic,retain)IBOutlet UIButton *pressit;
#property (nonatomic,retain)IBOutlet UIButton *seeya;
#property (nonatomic,retain)UIActivityIndicatorView *activity;
-(NSString *) genRandStringLength:(int) len ;
-(void)saveImagesFromPickerInTheBackgroundUsingImage:(UIImage *)img;
-(NSArray *)buildFilePaths;
- (IBAction)snapShots:(UIButton *)button;
-(IBAction)byebye:(id)sender;
#end
//=====================
//tester.m
#import "tester.h"
#import "MultiMediaUtilities.h"
#implementation tester
#synthesize imgPicker;
#synthesize pressit,seeya,activity;
//Image size constants
#define MAX_THUMBNAIL_RES_SIZE 103
#define MAX_IMAGE_RES_SIZE 640
- (IBAction)snapShots:(UIButton *)button
{
if (!imgPicker) imgPicker = [[UIImagePickerController alloc]init];
imgPicker.sourceType = UIImagePickerControllerSourceTypeCamera;
imgPicker.delegate = self;
[self presentModalViewController:imgPicker animated:YES];
}
- (void) imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info
{
UIImage *memoImage = [[MultiMediaUtilities scaleAndRotateImage:[info objectForKey:#"UIImagePickerControllerOriginalImage"] toResolution:MAX_IMAGE_RES_SIZE ]retain];
UIImageWriteToSavedPhotosAlbum(memoImage, self, #selector(image:didFinishSavingWithError:contextInfo:), nil);
[self saveImagesFromPickerInTheBackgroundUsingImage:memoImage];
// Dismiss the camera
[self dismissModalViewControllerAnimated:YES];
}
//builds paths to files in system with components
-(NSArray *)buildFilePaths
{
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
NSString *docsPath = [documentsDirectory stringByAppendingPathComponent:#"imagesfolder"];
NSString *fullDocsPath = [docsPath stringByAppendingPathComponent:#"assets"];
NSString *fullThumbsPath = [fullDocsPath stringByAppendingPathComponent:#"thumbs"];
NSArray * retArray = [NSArray arrayWithObjects:fullDocsPath,fullThumbsPath,nil];
return retArray;
}
-(void)saveImagesFromPickerInTheBackgroundUsingImage:(UIImage *)img
{
#try
{
NSFileManager *NSFm = [NSFileManager defaultManager];
NSArray *pathsArray = [NSArray arrayWithArray:[self buildFilePaths]];
NSString *fullDocsPath = [NSString stringWithFormat:#"%#", (NSString *)[pathsArray objectAtIndex:0]];
NSString *fullThumbsPath = [NSString stringWithFormat:#"%#", (NSString *)[pathsArray objectAtIndex:1]];
//Ensure Folders exist
BOOL isDir=YES;
NSError *error;
if(![NSFm fileExistsAtPath:fullDocsPath isDirectory:&isDir])
if(![NSFm createDirectoryAtPath:fullDocsPath withIntermediateDirectories:YES attributes:nil error:&error])
NSLog(#"Error: Create Images folder failed");
//create thumbs folder too
if(![NSFm fileExistsAtPath:fullThumbsPath isDirectory:&isDir])
if(![NSFm createDirectoryAtPath:fullThumbsPath withIntermediateDirectories:YES attributes:nil error:&error])
NSLog(#"Error: Create Thumbs folder failed");
//build the filenames & paths
NSString *newImageName= [NSString stringWithFormat:#"%#.png", [self genRandStringLength:10]];
NSString *imagePath = [[fullDocsPath stringByAppendingPathComponent:newImageName]retain];
NSLog(#"SavingIMage ImagePath = %#",imagePath);
NSString *thumbPath = [[fullThumbsPath stringByAppendingPathComponent:newImageName]retain];
NSLog(#"SavingIMage thumbPAth = %#",thumbPath);
//Write the files out
NSData *imgData = UIImagePNGRepresentation(img);
[imgData writeToFile:imagePath options:NSDataWritingAtomic error:&error];
if (!error) {
NSLog(#"Error writing image %#",error.description);
}
NSData *thumbData = UIImagePNGRepresentation(img);
[thumbData writeToFile:thumbPath options:NSDataWritingAtomic error:&error];
if (!error) {
NSLog(#"Error writing thumb %#",error.description);
}
}
#catch (NSException * e)
{
NSLog(#"Exception: %#", e);
}
}
-(NSString *) genRandStringLength:(int) len
{
NSString *letters = #"abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
NSMutableString *randomString = [NSMutableString stringWithCapacity: len];
for (int i=0; i<len; i++)
{
[randomString appendFormat: #"%c", [letters characterAtIndex: rand()%[letters length]]];
}
return randomString;
}
- (void)image:(UIImage*)image didFinishSavingWithError:(NSError *)error contextInfo:(NSDictionary*)info {
NSString *message;
NSString *title;
if (!error)
{
title = #"Camera...";
message = #"Image saved!...Just as well.";
}
else
{
title = #"Error";
message = [error description];
}
UIAlertView *alert = [[UIAlertView alloc]
initWithTitle:title
message:message
delegate:self
cancelButtonTitle:#"OK"
otherButtonTitles:nil];
[alert show];
[alert release];
if (image !=NULL){
[image release];
image=nil;
}
if(info !=NULL)
{
[info release];
info=nil;
}
}
- (void)viewDidUnload
{
[super viewDidUnload];
// Release any retained subviews of the main view.
// e.g. self.myOutlet = nil;
}
-(void)dealloc
{
[imgPicker release];
[pressit release];
[seeya release];
[activity release];
[super dealloc];
}
#end

Answer 1

Even seeded, this is an inappropriate use of random numbers.
Three approaches:
Use an incremented sequence number. (1, 2, 3, etc.)
Use a UUID from [[NSProcessInfo processInfo] globallyUniqueString]
Use a filename constructed from the date & time.

Answer 2

As Mats said, if you don't initialize your random number generator with srand, rand() will behave strangely and don't expect it to generate random numbers. This can cause the same filenames you experience.