在iOS应用启动之间目录不持久

Question

So I'm trying to store some data between openings of an app I'm making, but for some reason the directory I'm making and the data I'm storing aren't persisting between app openings, and I can't figure out why…

I have three methods:

- (NSString *)pathForDataFile 
{
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSLibraryDirectory, NSUserDomainMask,     YES);
    NSString *documentsDirectory = [paths objectAtIndex:0];
    documentsDirectory = [documentsDirectory stringByAppendingPathComponent:@"MyApp"];
    NSLog(@"%@", documentsDirectory);

    NSError *error;
    NSLog(@"%i", (int)[[NSFileManager defaultManager] createDirectoryAtPath:documentsDirectory withIntermediateDirectories:YES attributes:nil error:&error]);   

    return documentsDirectory;
}

- (void)saveDataToDisk 
{
    NSString * path = [self pathForDataFile];

    NSMutableDictionary * rootObject;
    rootObject = [NSMutableDictionary dictionary];

    [rootObject setValue: [self usedPlaces] forKey:@"key"];
    [NSKeyedArchiver archiveRootObject: rootObject toFile: path];
}

- (void) loadDataFromDisk
{
    NSString     * path = [self pathForDataFile];
    NSDictionary * rootObject;

    rootObject = [NSKeyedUnarchiver unarchiveObjectWithFile:path];    
    [self setObject: [rootObject valueForKey:@"key"]];
}

When I print out the result of creating the directory in pathForDataFile , every time it prints 1, which means every time it's creating that directory, even though it shouldn't be able to since the directory should already exist after one call. saveDataToDisk is called in applicationWillTerminate , and loadDataFromDisk is called in applicationDidBecomeActive . Can anybody help me as to why this is happening?

Answer 1

You need to do some additional error checking in your code to try to narrow down where the problem is actually happening.

Error checking like the new lines in your original sample code:

- (NSString *)pathForDataFile 
{
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSLibraryDirectory, NSUserDomainMask, YES);
    NSString *documentsDirectory = [paths objectAtIndex:0];
    documentsDirectory = [documentsDirectory stringByAppendingPathComponent:@"MyApp"];
    BOOL success = [[NSFileManager defaultManager] createDirectoryAtPath:documentsDirectory withIntermediateDirectories:YES attributes:nil error:&error];
    // success is NO only if there is an error.  success is YES if directory was created or if the directory already exists
    if(success == NO)
    {
        NSLog( @"error creating directory at path %@ is %@", documentsDirectory, [error localizedDescription] );
    }

    return documentsDirectory;
}

- (void)saveDataToDisk 
{
    NSString * path = [self pathForDataFile];
    if(([self usedPlaces] == NULL) || ([self usedPlaces count] == 0))
    {
        NSLog( @"usedPlaces is either null or has no entries");
    }
    NSDictionary * rootObject = [NSDictionary dictionaryWithObject: [self usedPlaces] forKey: @"key"];
    BOOL success = [NSKeyedArchiver archiveRootObject: rootObject toFile: path];
    if(success == NO)
    {
        NSLog( @"was not able to write data to path %@", path );
    }
}

- (void) loadDataFromDisk
{
    NSString     * path = [self pathForDataFile];
    NSDictionary * rootObject;

    rootObject = [NSKeyedUnarchiver unarchiveObjectWithFile:path];
    if(rootObject)
        [self setObject: [rootObject valueForKey:@"key"]];
    else
        NSLog( @"was not able to load data from file at %@", path );
}