Saved files no longer exists after closing the app - ios

Question

I am downloading a file using NSURLSessionDownloadTask. it get downloaded and saved. and I can display data normally.
Unfortunitly I only have the iOS simulator to test. What is happenning if I close the app with the stop button on Xcode. then I relaunch, the file is no longer exists.
But, If I closed it by removing it from apps. running list by clicking cmd + shift + H twice. and reluanch it by tapping app. on simulator. I find the file.
BOOL found = [[NSFileManager defaultManager] fileExistsAtPath:path];
Is this a simulator problem? and I shouldn't worry about it in a real device?
Actually, I just managed to test on iPhone. exactly the same behaviour!! Any explanation.
I call this on the NSURLSessionDownloadTask which I sent a destination block that returns the destination to save:
- (NSURLSessionDownloadTask *)downloadTaskWithRequest:(NSURLRequest *)request
progress:(NSProgress * __autoreleasing *)progress
destination:(NSURL * (^)(NSURL *targetPath, NSURLResponse *response))destination
completionHandler:(void (^)(NSURLResponse *response, NSURL *filePath, NSError *error))completionHandler
Destination block code:
NSURL *documentsDirectoryURL = [[NSFileManager defaultManager] URLForDirectory:NSLibraryDirectory inDomain:NSUserDomainMask appropriateForURL:nil create:NO error:nil];
return [documentsDirectoryURL URLByAppendingPathComponent:[response suggestedFilename]];

Answer 1

Try to log documentsDirectoryURL and you will see that it is different each time you launch the app. Solution is to save between launches not an absolute URL, but a path relative to NSLibraryDirectory directory. I had the same problem and I have solved it with two methods:
// [self uploadFolder] returns a folder in NSLibraryDirectory
+ (NSString*)relativePathForURL:(NSURL*)url
{
NSURL *uploadFolderURL = [self uploadFolder];
if ([url.baseURL isEqual:uploadFolderURL])
{
return url.relativeString;
}
else if ([url.absoluteString hasPrefix:uploadFolderURL.absoluteString])
{
return [url.absoluteString substringFromIndex:uploadFolderURL.absoluteString.length];
}
return nil;
}
+ (NSURL*)urlForRelativePath:(NSString*)path
{
return [NSURL URLWithString:path relativeToURL:[self uploadFolder]];
}
They should be used following way:
Download file and move it to NSLibraryDirectory folder with some URL
savedURL.
Call relativePath = [self relativePathForURL:savedURL] and save it.
When app is relaunched call savedURL = [self urlForRelativePath:relativePath]
savedURL is valid now.

Answer 2

Heres the solution;
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didFinishDownloadingToURL:(NSURL *)location{
//location is the temporary "destination" which you returned (can be Temp directory) and it now contains the downloaded file. Now copy the file to a new location (eg documents directory) for future use.
BOOL fileCopied = [[[NSFileManager defaultManager] copyItemAtURL:location toURL:documentsDirectoryURLForSavingFileForFutureUe error:&error];
}