iPhone save data getting deleted on upgrade?

Question

I have an app in the app store, and just got a message from a user telling me that upon upgrading to a newer version of the app, their saved data all disappeared.

Is there a distinctly wrong way to save data on the iphone that would cause data loss upon upgrading the app to a new version?

Here is the code I'm using to load & save, which works fine on development machines. Is this the wrong way to do it?

- (bool) saveData:(NSData*) data toFile:(NSString*) filename
{
    NSError* error;

    NSFileManager *fileMgr = [[[NSFileManager alloc] init] autorelease];
    NSString *docsDir = [NSHomeDirectory() stringByAppendingPathComponent:@"Documents"];
    NSString* filePath = [docsDir stringByAppendingPathComponent:filename];
    NSString* validMarkerPath = [docsDir stringByAppendingPathComponent:[filename stringByAppendingString:@".val"]];
    NSString* backupPath = [docsDir stringByAppendingPathComponent:[filename stringByAppendingString:@".bak"]];

    // If the file exists and is marke valid, copy it over the backup.
    if([fileMgr fileExistsAtPath:filePath] && [fileMgr fileExistsAtPath:validMarkerPath])
    {
        if([fileMgr fileExistsAtPath:backupPath])
        {
            if(![fileMgr removeItemAtPath:backupPath error:&error])
            {
                NSLog(@"Error: SafeFileManager: Could not remove backup file %@: %@", backupPath, [error localizedDescription]);
            }
        }

        if(![fileMgr moveItemAtPath:filePath toPath:backupPath error:&error])
        {
            NSLog(@"Error: SafeFileManager: Could not move %@ to %@: %@", filePath, backupPath, [error localizedDescription]);
        }
    }

    // Remove the "valid" marker file, if present.
    if([fileMgr fileExistsAtPath:validMarkerPath])
    {
        if(![fileMgr removeItemAtPath:validMarkerPath error:&error])
        {
            NSLog(@"Error: SafeFileManager: Could not remove validation file %@: %@", validMarkerPath, [error localizedDescription]);
        }
    }

    // Save the new file.
    if(![data writeToFile:filePath options:NSAtomicWrite error:&error])
    {
        NSLog(@"Error: SafeFileManager: Could not save to %@: %@", filePath, [error localizedDescription]);
        return NO;
    }

    // If we succeeded, save the "valid" marker file.
    NSData* markerData = [NSData dataWithBytes:"0" length:1];
    if(![markerData writeToFile:validMarkerPath options:NSAtomicWrite error:&error])
    {
        NSLog(@"Error: SafeFileManager: Could not save validation file %@: %@", validMarkerPath, [error localizedDescription]);
        return NO;
    }
    return YES;
}

- (NSData*) loadDataFromFile:(NSString*) filename
{
    NSError* error;

    NSFileManager *fileMgr = [[[NSFileManager alloc] init] autorelease];
    NSString *docsDir = [NSHomeDirectory() stringByAppendingPathComponent:@"Documents"];
    NSString* filePath = [docsDir stringByAppendingPathComponent:filename];
    NSString* validMarkerPath = [docsDir stringByAppendingPathComponent:[filename stringByAppendingString:@".val"]];

    // If the file isn't valid, we'll try to load the backup.
    if(![fileMgr fileExistsAtPath:validMarkerPath])
    {
        filePath = [docsDir stringByAppendingPathComponent:[filename stringByAppendingString:@".bak"]];
    }

    NSData* data = nil;

    @try
    {
        data = [NSData dataWithContentsOfFile:filePath options:NSUncachedRead error:&error];
        if(nil == data)
        {
            NSLog(@"Error: SafeFileManager: Could not load from %@: %@", filePath, [error localizedDescription]);
        }
    }
    @catch (NSException * e)
    {
        NSLog(@"Error: SafeFileManager: Could not load from %@: %@", filePath, [e description]);
        data = nil;
    }

    return data;
}

Answer 1

To answer my own question, this code does have a write hole where the backup file and marker file are deleted, which would cause the load to fail.

I've now opted for a simpler, if not more brute-force approach of simply saving the file, then saving a backup. On load, it tries the main file, and if any error occurs whatsoever, it attempts the same load routine using the backup file.