将文件下载到Documents目录

Question

I'm trying to copy a downloaded file to a specific folder in the app's documents directory but can't seem to get it working. The code I'm using is:

NSString *itemPathString = @"http://pathToFolder/folder/myFile.doc";
NSURL *myUrl = [NSURL URLWithString:itemPathString];

NSArray *paths = [fm URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask];

NSURL *folderPath = [[paths objectAtIndex:0] URLByAppendingPathComponent:@"folder"];
NSURL *itemURL = [documentsPath URLByAppendingPathComponent:@"myFile.doc"];

// copy to documents directory asynchronously
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

    NSFileManager *theFM = [[NSFileManager alloc] init];
    NSError *error;
    [theFM copyItemAtURL:myUrl toURL:itemURL error:&error];
    }
});

I can retrieve the file OK but can't copy it. Can anyone tell me if there's anything wrong with the above code?

Answer 1

If downloading a file from a server, if it's a reasonably small file (eg measured in kb, not mb), you can use dataWithContentsOfURL . You can use that method to load the file into memory, and then use the NSData instance method writeToFile to save the file.

But, if it's a larger file, you will want to use NSURLConnection , which doesn't try to hold the whole file in memory, but rather writes it to the file system when appropriate. The trick here, though, is if you want to download multiple files, you either have to download them sequentially, or encapsulate the NSURLConnection and the NSOutputStream such that you can have separate copies of those for each simultaneous download.

I have uploaded a project, Download Manager that demonstrates what a NSURLConnection implementation might look like, but it's non-trivial. You might rather want to contemplate using an established, third-party library, such as ASIHTTPRequest or RestKit .

Answer 2

If you want to access a folder with a given name you should check if it exists and if not create it. That could quite easy be done like this:

NSString *folder = [documentsPath stringByAppendingPathComponent:folderName];
NSFileManager *fileManager = [NSFileManager defaultManager];
NSError *error = nil;
if (![fileManager fileExistsAtPath:folder]) {
    [fileManager createDirectoryAtPath:folder withIntermediateDirectories:YES attributes:nil error:&error];
}
if (error != nil) {
    NSLog(@"Some error: %@", error);
    return;
}

EDIT

If you want to check if the folder was created properly on your device got to Organizer -> Devices -> [YourDevelopingDeviceWhereTheAppWasInstalled] -> Applications -> [YourApplication]

In the lower section you should at least see some folders like Documents. And if successful your created folders as well.

Answer 3

You need to create any intermediate directories prior to copying files. Check in the Simulator folder to see wether the "folder" directory is created in the applications Documents-folder.

Path to simulator is /Users/$username/Library/Application Support/iPhone Simulator/