Proper way of handling reference to NSError

Question

My code looks like this, sometimes app crashes on the last line, when it tries to log the error. What am I doing wrong?

BOOL isDir;
NSError *error;
NSString *downloadPath = [[NSString stringWithFormat:@"%@/%@", [download downloadFolder], [download escapedTitle]] stringByExpandingTildeInPath];
NSFileManager *fileManager = [NSFileManager defaultManager];

if (![fileManager fileExistsAtPath:downloadPath isDirectory:&isDir])
{
    [fileManager createDirectoryAtPath:downloadPath withIntermediateDirectories:YES attributes:nil error:&error];

    if (error)
        NSLog(@"%@", [error localizedDescription]);
}

I've also attached the output from the console:

Answer 1

In Cocoa, the NSError ** is only valid if the called method returns an error, which in this case would be if -createDirectoryAtPath:... returns false.

Instead of testing for if (error), test for the return value of the -createDirectoryAtPath: method being false, and you'll be good to go.

For example:

if (![fileManager createDirectoryAtPath:downloadPath withIntermediateDirectories:YES attributes:nil error:&error]) {
    NSLog(@"%@", [error localizedDescription]);
}