How to download file using asynchronous request? - ios

Question

Now, when my app detect that file was updated on server, it download file and user interface stuck for downloading time. I have ASIHTTPRequest wrapper in my app, but I doesn't know how to change my download request to asynchronous.
My code:
- (void)downloadFileIfUpdated
{
NSString *urlString = #"http://www.mysite.com/data.plist";
NSLog(#"Downloading HTTP header from: %#", urlString);
NSURL *url = [NSURL URLWithString:urlString];
NSArray *documentPaths = NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES);
NSString *cachedPath = [[documentPaths lastObject] stringByAppendingPathComponent:#"data.plist"];
NSFileManager *fileManager = [NSFileManager defaultManager];
BOOL downloadFromServer = NO;
NSString *lastModifiedString = nil;
NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
[request setHTTPMethod:#"HEAD"];
NSHTTPURLResponse *response;
[NSURLConnection sendSynchronousRequest:request returningResponse:&response error: NULL];
if ([response respondsToSelector:#selector(allHeaderFields)]) {
lastModifiedString = [[response allHeaderFields] objectForKey:#"Last-Modified"];
}
NSDate *lastModifiedServer = nil;
#try {
NSDateFormatter *df = [[NSDateFormatter alloc] init];
df.dateFormat = #"EEE',' dd MMM yyyy HH':'mm':'ss 'GMT'";
df.locale = [[NSLocale alloc] initWithLocaleIdentifier:#"en_US"];
df.timeZone = [NSTimeZone timeZoneWithAbbreviation:#"GMT"];
lastModifiedServer = [df dateFromString:lastModifiedString];
}
#catch (NSException * e) {
NSLog(#"Error parsing last modified date: %# - %#", lastModifiedString, [e description]);
}
NSLog(#"lastModifiedServer: %#", lastModifiedServer);
NSDate *lastModifiedLocal = nil;
if ([fileManager fileExistsAtPath:cachedPath]) {
NSError *error = nil;
NSDictionary *fileAttributes = [fileManager attributesOfItemAtPath:cachedPath error:&error];
if (error) {
NSLog(#"Error reading file attributes for: %# - %#", cachedPath, [error localizedDescription]);
}
lastModifiedLocal = [fileAttributes fileModificationDate];
NSLog(#"lastModifiedLocal : %#", lastModifiedLocal);
[activityIndicator stopAnimating];
}
// Download file from server if we don't have a local file
if (!lastModifiedLocal) {
downloadFromServer = YES;
}
// Download file from server if the server modified timestamp is later than the local modified timestamp
if ([lastModifiedLocal laterDate:lastModifiedServer] == lastModifiedServer) {
[activityIndicator startAnimating];
downloadFromServer = YES;
}
if (downloadFromServer) {
NSLog(#"Downloading new file from server");
NSData *data = [NSData dataWithContentsOfURL:url];
if (data) {
// Save the data
if ([data writeToFile:cachedPath atomically:YES]) {
NSLog(#"Downloaded file saved to: %#", cachedPath);
}
// Set the file modification date to the timestamp from the server
if (lastModifiedServer) {
NSDictionary *fileAttributes = [NSDictionary dictionaryWithObject:lastModifiedServer forKey:NSFileModificationDate];
NSError *error = nil;
if ([fileManager setAttributes:fileAttributes ofItemAtPath:cachedPath error:&error]) {
NSLog(#"File modification date updated");
[NSThread detachNewThreadSelector:#selector(loadPList) toTarget:self withObject:nil];
[activityIndicator stopAnimating];
}
if (error) {
NSLog(#"Error setting file attributes for: %# - %#", cachedPath, [error localizedDescription]);
}
}
}
}
}

Answer 1

NSURL *url = [NSURL URLWithString:#"http://allseeing-i.com"];
__block ASIHTTPRequest *request = [ASIHTTPRequest requestWithURL:url];
[request setCompletionBlock:^{
// Use when fetching text data
NSString *responseString = [request responseString];
// Use when fetching binary data
NSData *responseData = [request responseData];
}];
[request setFailedBlock:^{
NSError *error = [request error];
}];
[request startAsynchronous];
For more details look at http://allseeing-i.com/ASIHTTPRequest/How-to-use#using_blocks