iPhone 升级时保存的数据被删除？

Question

我在应用程序商店中有一个应用程序，刚刚收到用户的一条消息，告诉我在升级到该应用程序的新版本后，他们保存的数据全部消失了。

是否有一种明显错误的方式在 iPhone 上保存数据，导致应用程序升级到新版本时会导致数据丢失？

这是我用来加载和加载的代码save，在开发机器上运行良好。这是错误的做法吗？

- (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

为了回答我自己的问题，这段代码确实有一个写入漏洞，其中备份文件和标记文件被删除，这会导致加载失败。

我现在选择了一种更简单（如果不是更暴力）的方法，即简单地保存文件，然后保存备份。加载时，它会尝试主文件，如果发生任何错误，它会使用备份文件尝试相同的加载例程。