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null。此外，当您创建目录时，是否意味着您在指定的URL路径创建文件夹？继承人我正在使用的代码

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

您的代码存在一些问题。

此：

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]];

此：

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

应该是：

NSString *urlString = [url path];

此：

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];

此：

[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代替path将URL转换为文件路径。辅助节点在创建目录时传递文件名而不是路径。不必要地使用stringWithFormat:并没有引起任何问题，但请立即打破这种习惯。实际需要格式化字符串时，只能使用stringWithFormat:。不需要将字符串分配给字符串变量。

Answer 2

您没有为目录中的图像指定文件名，这可以通过在创建目录后立即添加此行来解决：


    // Right after the directory is created (I suppose the format is png) :
    url = [url URLByAppendingPathComponent:@"image.png"];

    // Now you can continue with the rest of your code :

    //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 3

我从未创建过文件管理器的实例。我总是简单地使用默认值看看这是否有帮助：

NSFileManager *manager = [NSFileManager defaultManager];

NSFileManager不保存数据

3 个答案: