Simplest way on iPhone to unzip downloaded file?

问题:

Goal: download a zipped file, unzip it, and save it in the iPhone app's Documents directory.

The following code makes use of the initWithGzippedData method that was added to NSData in the Molecule app found here: http://www.sunsetlakesoftware.com/molecules

As adapted to my app:

NSString *sFolder = [NSHomeDirectory() stringByAppendingPathComponent:@"Documents"];
NSString *sFileName = [sFolder stringByAppendingPathComponent:@"MyFile.db"];
NSURL *oURL = [NSURL URLWithString: @"http://www.isystant.com/Files/MyFile.zip"];
NSData *oZipData = [NSData dataWithContentsOfURL: oURL];
NSData *oData = [[NSData alloc] initWithGzippedData:oZipData];
[oZipData release];
b = [oData writeToFile:sFileName atomically:NO];
NSLog(@"Unzip %i", b);

Result: A zip file is successfully downloaded. From it a new, supposedly unzipped file is created in the Documents directory with the desired name (MyFile.db) but it has zero bytes.

Anybody see the problem? Or else is there a simpler way to unzip a downloaded file than the one used in the Molecules app?

回答1:

I think that your problem may be that you are attempting to gzip-deflate a Zip file. Those are two different compression algorithms.

I based the gzip-deflating code in Molecules on this NSData category (the code of which I've copied into this answer) provided by the contributors to the CocoaDev wiki. What you'll want to do is use their -zlibDeflate implementation, which should properly unzip a Zip file.

Unrelated to your problem, instead of using NSHomeDirectory() and appending a path component, the recommended approach for finding the documents directory is the following:

NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];

回答2:

You should make sure your file is never too big, as you are loading it fully into memory before the unzip starts.