Question

I use NSData to persist an image in my application. I save the image like so (in my App Delegate):

- (void)applicationWillTerminate:(UIApplication *)application
{
    NSLog(@"Saving data");

    NSData *data = UIImagePNGRepresentation([[viewController.myViewController myImage]image]);
    //Write the file out!

    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentsDirectory = [paths objectAtIndex:0];

    NSString *path_to_file = [documentsDirectory stringByAppendingString:@"lastimage.png"];

    [data writeToFile:path_to_file atomically:YES];
    NSLog(@"Data saved.");
}

and then I load it back like so (in my view controller, under viewDidLoad):

NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];

NSString *path_to_file = [documentsDirectory stringByAppendingString:@"lastimage.png"];

if([[NSFileManager defaultManager] fileExistsAtPath:path_to_file])
{
    NSLog(@"Found saved file, loading in image");
    NSData *data = [NSData dataWithContentsOfFile:path_to_file];

    UIImage *temp = [[UIImage alloc] initWithData:data];
    myViewController.myImage.image = temp;
    NSLog(@"Finished loading in image");
}

This code works every time on the simulator, but on the device, it can never seem to load back in the image. I’m pretty sure that it saves out, but I have no view of the filesystem.

Am I doing something weird? Does the simulator have a different way to access its directories than the device?

Thanks!

Answer 1

Aha! Nailed it!

I’m writing this so someone else pulling their hair doesn’t sit there staring at code, wondering why it doesn’t work 🙂

The problematic line is this one:

NSString *path_to_file = [documentsDirectory stringByAppendingString:@"lastimage.png"];

It should look like this:

NSString *path_to_file = [documentsDirectory stringByAppendingPathComponent:@"lastimage.png"];

The reason for this is, without it, you’d get something along the lines of /Files/Documentslastimage.png instead of /Files/Documents/lastimage.png, as the path component appending takes care of the slashes for you. I hope this helps someone else in the future!