Here’s a frequent function necessary for checking the most-up-to-date content. Note that KURL is a constant string defined elsewhere:
NSString *documentsPath = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,
NSUserDomainMask, YES)
objectAtIndex:0];
NSString *isiSavedFilePath = [documentsPath
stringByAppendingPathComponent:@”myFile.pdf”];
NSURL *isiURL = [NSURL fileURLWithPath:isiSavedFilePath];
// if file doesn’t exist, download it
if (![[NSFileManager defaultManager] fileExistsAtPath:isiSavedFilePath] &&
[self isConnected]) {
NSData *pdfData =
[[NSDataalloc] initWithContentsOfURL:[NSURLURLWithString:KURL]];
//Store the downloaded file in documents directory as a NSData format
[pdfData writeToFile:isiSavedFilePath atomically:YES];
} else {
if ([self isConnected]) {
// if the file is stored, compare the file modified date.
// create a HTTP request to get the file information from the web server
NSURL* url = [NSURL URLWithString:KISIURL];
NSMutableURLRequest* request = [NSMutableURLRequestrequestWithURL:url];
[request setHTTPMethod:@”HEAD”];
NSHTTPURLResponse* response;
[NSURLConnectionsendSynchronousRequest:request
returningResponse:&response error:nil];
// get the last modified info from the HTTP header
NSString *httpLastModified = nil;
if ([response respondsToSelector:@selector(allHeaderFields)]) {
httpLastModified = [[response allHeaderFields]
objectForKey:@”Last-Modified”];
}
// setup a date formatter to query the server file’s modified date
NSDateFormatter *df = [[NSDateFormatteralloc] init];
df.dateFormat = @”EEE’,’ dd MMM yyyy HH’:’mm’:’ss ‘GMT'”;
df.locale = [[NSLocalealloc] initWithLocaleIdentifier:@”en_US”];
df.timeZone = [NSTimeZonetimeZoneWithAbbreviation:@”GMT”];
// get the file attributes to retrieve the local file’s modified date
NSDictionary *fileAttributes =
[[NSFileManagerdefaultManager] attributesOfItemAtPath:isiSavedFilePath error:nil];
// test if the server file’s date is later than the local file’s date
NSDate *serverFileDate = [df dateFromString:httpLastModified];
NSDate *localFileDate = [fileAttributes fileModificationDate];
BOOL isServerNewer = ([localFileDate laterDate:serverFileDate] == serverFileDate);
NSLog(@”isServerNewer = %d”, isServerNewer);
// and then replace it if it is newer.
if (isServerNewer) {
NSError *error;
[[NSFileManager defaultManager] removeItemAtPath:isiSavedFilePath error:&error];
NSData *pdfData =
[[NSDataalloc] initWithContentsOfURL:[NSURLURLWithString:KURL]];
//Store the downloaded file in documents directory as a NSData format
[pdfData writeToFile:isiSavedFilePath atomically:YES];
}
} else {
[[[UIAlertViewalloc] initWithTitle:@”No Internet”message:@”Not able to download the file until you connect to the Internet.”delegate:selfcancelButtonTitle:@”OK”otherButtonTitles:nil] show];
}
}
