Cannot write(add UIImage) to photo album

I have the following code

- (void)image:(UIImage *)image didFinishSavingWithError:(NSError *)error contextInfo:(void *)contextInfo{

NSLog(@"failed");
}

which checks for the error, and it prints out time I run the following

-(IBAction) addWallpaper{

UIImageWriteToSavedPhotosAlbum( [UIImage imageNamed:[NSString stringWithFormat:@"%d.png", r]]
                               , self, @selector(image:didFinishSavingWithError:contextInfo:), nil );
}

How do I correctly save开发者_如何学运维d the UIImage to the photo album?

Despite the name

- (void)image:(UIImage *)image didFinishSavingWithError:(NSError *)error
                               contextInfo:(void *)contextInfo

doesn't indicate an error. You need to check the error passed to this function.

Something like:

-(void)image:(UIImage *)image didFinishSavingWithError:(NSError*)error
                                  contextInfo:(void*)contextInfo
{
    UIAlertView *alert;
    if ( [error code] != 0 )
    {
            alert = [[UIAlertView alloc] initWithTitle:@"Sorry"
                       message:@"Things went wrong!"
                       delegate:nil
                       cancelButtonTitle:nil
                       otherButtonTitles:@"OK",nil];
    } else {
            alert = [[UIAlertView alloc] initWithTitle:@"Great"
                       message:@"Image was saved!"
                       delegate:nil
                       cancelButtonTitle:nil
                       otherButtonTitles:@"OK",nil];
    }
    [alert show];
    [alert release];
}