ios - NSFileManager 不保存数据

Question

我正在尝试将数据保存到 NSFileManager 创建的目录中，但是当我尝试检索数据和 NSLog 时，我得到的是空值。另外，当您创建一个目录时，是否意味着您在指定的 url 路径下创建了一个文件夹？这是我正在使用的代码

NSError *error = nil;
NSFileManager *manager = [[NSFileManager alloc] init];
NSArray *urlsArray = [manager URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask];
NSLog(@"%@", urlsArray);
// This will create a new url and append a photo title to the end
NSURL *url = [[urlsArray lastObject] URLByAppendingPathComponent:[NSString stringWithFormat:@"%@", [self.recentPhoto objectForKey:FLICKR_PHOTO_TITLE]]];
NSLog(@"%@", url);
NSString *urlString = [NSString stringWithFormat:@"%@", [url absoluteString]];
NSLog(@"%@", urlString);
//create the directory
if(![manager fileExistsAtPath:urlString isDirectory:YES]){
    BOOL success = [manager createDirectoryAtURL:url withIntermediateDirectories:YES attributes:nil error:&error];
    if (!success) {
        NSLog(@"Error creating data path: %@", [error localizedDescription]);
    }
}
//get url for a photo image and then store it.
NSURL *imageURL = [FlickrFetcher urlForPhoto:self.recentPhoto format:FlickrPhotoFormatLarge];
NSData *imageData = [[NSData alloc] initWithContentsOfURL:imageURL];
[imageData writeToURL:url atomically:YES];
//get data to check if its stored
NSData *checkImageData = [[NSData alloc] initWithContentsOfURL:url];
//This returns null
NSLog(@"%@", checkImageData);
//this returns 0
NSLog(@"%d", [manager isReadableFileAtPath:urlString]);

Answer 1

您的代码有几个问题。

这个:

NSURL *url = [[urlsArray lastObject] URLByAppendingPathComponent:[NSString stringWithFormat:@"%@", [self.recentPhoto objectForKey:FLICKR_PHOTO_TITLE]]];

应该是:

NSURL *url = [[urlsArray lastObject] URLByAppendingPathComponent:[self.recentPhoto objectForKey:FLICKR_PHOTO_TITLE]];

这个:

NSString *urlString = [NSString stringWithFormat:@"%@", [url absoluteString]];

应该是:

NSString *urlString = [url path];

这个:

BOOL success = [manager createDirectoryAtURL:url withIntermediateDirectories:YES attributes:nil error:&error];

应该是:

BOOL success = [manager createDirectoryAtURL:[url URLByDeletingLastPathComponent] withIntermediateDirectories:YES attributes:nil error:&error];

这个:

[imageData writeToURL:url atomically:YES];

应该是:

NSError *error = nil;
BOOL res = [imageData writeToURL:url options:NSDataWritingAtomic error:&error];
if (!res) {
    NSLog(@"Unable to write to %@: %@", url, error);
}

主要问题是使用 absoluteString 而不是 path 将 URL 转换为文件路径。 Secondary 在创建目录时传递的是文件名而不是路径。不必要地使用 stringWithFormat: 不会造成任何问题，但请立即改掉这个习惯。仅当您确实需要格式化字符串时才使用 stringWithFormat:。不需要将字符串分配给字符串变量。