FileExistAtPath在模拟器上运行，但在设备上不运行

Question

In my game, I'm saving stats of the player in a plist that I store in the Documents directory. I have an empty dictionary of each stats that should be saved named "Default_Stats.plist" so that if it's the first time the app is loaded, it will copy it in the appropriate directory so it could be loaded and overwritten at will. The problem is, every time my app is loaded, it doesn't recognize the "Stats.plist" and overwrite it with the Default Stats, resetting every stats the player have made... And weird enough, it was perfectly working on the simulator, but not on the device. Here's my code :

In this method I read the stats :

- (void) readStatsFromFile{
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *statsPath = [[paths objectAtIndex:0] stringByAppendingPathComponent:@"Stats.plist"];

    //Check if the file has already been created
    if (![[NSFileManager defaultManager] fileExistsAtPath:statsPath]){
        [self createStatsList];
    }else{
        stats = [[NSMutableDictionary dictionaryWithContentsOfFile:statsPath]retain];
    }
}

Here's my creating method :

- (void) createStatsList{
    NSString *statsPath = [[NSBundle mainBundle] bundlePath];
    statsPath = [statsPath stringByAppendingPathComponent:@"Default_Stats.plist"];

    stats = [[NSMutableDictionary dictionaryWithContentsOfFile:statsPath] retain];

    [self writeStatsToFile];
}

And my writing method :

- (void) writeStatsToFile{
    BOOL ok;
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *statsPath = [[paths objectAtIndex:0] stringByAppendingPathComponent:@"Stats.plist"];
    ok = [stats writeToFile:statsPath atomically:YES];

    if (!ok) {
        NSLog(@"Couldn't write to file");
    }else
        NSLog(@"Stats written succesfully!");
}

Please help, I really don't understand what's wrong! I hope I've made myself clear enough!

Answer 1

使用文件路径而不是绝对路径。

Answer 2

Maybe duplicates exist in your mac, which makes exists=true on simulator, but not on device.

The easiest way to check would be to NSLog the paths encountered. Refer to these tools - they allow console logs to be captured for release builds running on your device.

Answer 3

Most likely that your documents directory just doesn't exist - on the simulator you share a documents directory with everyone on the Mac; on the device everyone has his own directory. Use the file manager method

createDirectoryAtURL:url withIntermediateDirectories:YES

to make sure that the directory is there before you try writing there. (I tend to use the URL methods instead of the file path methods).

PS. I'd recommend having one method that returns the path or url that you want. It's a good habit not to duplicate your code again and again.

Answer 4

I would do pretty much that, like everything in one session:

1. gets the URL for the file in the Document folder;
2. if the file is not there yet, copies the file from bundle to the Documents folder;

---

that should be the method for that, I have defined some macros for avoiding mistyping the file's name in the code:

- (NSURL *)statsFileURL {
#define NSStringFromFileNameWithExtension(filename, extension) [(filename) stringByAppendingPathExtension:(extension)]
#define kExtension @"plist"
#define kDefaultStatsFileName @"Default_Stats"
#define kCustomStatsFileName @"Stats"

    NSURL *_returnURL = nil;

    NSFileManager *_fileManager = [NSFileManager defaultManager];
    NSURL *_documentDirectory = [[_fileManager URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask] lastObject];
    NSURL *_myFileURLInDocumentFolder = [_documentDirectory URLByAppendingPathComponent:NSStringFromFileNameWithExtension(kDefaultStatsFileName, kExtension)];
    if ([_fileManager fileExistsAtPath:[_myFileURLInDocumentFolder path]]) {
        _returnURL = _myFileURLInDocumentFolder;
    } else {
        NSURL *_myFileURLInBundle = [[NSBundle mainBundle] URLForResource:kDefaultStatsFileName withExtension:kExtension];
        if ([_fileManager fileExistsAtPath:[_myFileURLInBundle path]]) {
            NSError *_error = nil;
            if ([_fileManager copyItemAtURL:_myFileURLInBundle toURL:_myFileURLInDocumentFolder error:&_error]) {
                if (_error == nil) {
                    _returnURL = _myFileURLInDocumentFolder;
                } else {
                    // some error during copying
                }
            } else {
                // some error during copying
            }
        } else {
            // the file does not esixts at all, not even in the bundle
        }
    }

    return _returnURL;
}

the URL always points inside the Documents folder, so you will have read/write access to the file – or will be nil if some error happens.

after you have the URL , you can restore back to file without any issue, and at some other point in runtime you can override the file for your convenience anytime.

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NOTE: you may need to extend this code for a more detailed error handling, I put the comment only the places when you need to worry about potential errors.