UIAlertView is showing up late - iphone

Question

I am communicating with server in my ios app. I have following method in which I'm opening an alertview. I want to show a loading view while app is getting response from the server.
- (void) showDetailedQuestion:(id)sender
{
//loading view
self.loading_alert = [[UIAlertView alloc] initWithTitle:#"Loading\nPlease Wait..." message:nil delegate:self cancelButtonTitle:nil otherButtonTitles: nil];
[self.loading_alert show];
UIActivityIndicatorView *indicator = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleWhiteLarge];
// Adjust the indicator so it is up a few pixels from the bottom of the alert
indicator.center = CGPointMake(loading_alert.bounds.size.width / 2, loading_alert.bounds.size.height - 50);
[indicator startAnimating];
[self.loading_alert addSubview:indicator];
UIButton *btn = (UIButton*)sender;
int indx = btn.tag;
NSLog(#"tag:%d",indx);
answerAnQuestion *vc = [self.storyboard instantiateViewControllerWithIdentifier:#"Answer"];
vc.modalTransitionStyle = UIModalTransitionStyleFlipHorizontal ;
vc.que_id = [self.que_id valueForKey:[NSString stringWithFormat:#"%d",indx]];
vc.qid_list = self.que_id;
vc.crnt = indx;
[self presentViewController:vc animated:YES completion:nil];
[self.loading_alert dismissWithClickedButtonIndex:0 animated:YES];
}
and in another answerAnQuestion.m
- (void)viewDidLoad
{
NSString *address = [NSString stringWithFormat:#"%#%#%#%#%#%#%#", path,#"questions/",que_id,#"?token=",token,#"&user_id=",usrId];
NSURL *URL = [NSURL URLWithString:address];
NSLog(#"%#",address);
[NSURLRequest setAllowsAnyHTTPSCertificate:YES forHost:[URL host]];
NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:URL cachePolicy:NSURLCacheStorageAllowedInMemoryOnly
timeoutInterval:60.0];
[request setHTTPMethod:#"GET"];
responseData = [[NSMutableData alloc] init];
NSURLResponse *response = nil;
NSError *error = nil;
NSData *data = [NSURLConnection sendSynchronousRequest:request returningResponse:&response error:&error];
if (data)
{
NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse*) response;
//If you need the response, you can use it here
int statuscode = [httpResponse statusCode];
NSString *responseMsg = [NSHTTPURLResponse localizedStringForStatusCode:statuscode];
NSLog(#" Status code: %d",statuscode );
NSLog(#" Status msg: %#",responseMsg );
}
else
{
// Handle error by looking at response and/or error values
NSLog(#"%#",error);
}
}
My problem is alertview is only shown up for a moment when view is changing. It suppose to open when I click the button. What could be the reason? how to solve this?
EDIT 1:
If i make asynchronous request to server then i'm not able to set those data in my tableview. I can set those data in my tableview Only if send synchronous request,but it blocks the app. Why this is happening ?
Any help will be appreciated.
Thank you.

Answer 1

You are sending SynchronousRequest on main thread, so it is blocking your UI thread. Read multithreading you will get various tutorial on this. I can suggest you to go for GCD or NSOperation and NSOperationQueue. Google for any of the above and you will get various sample for the same.
Or you can send asynchronous request as follows...
[NSURLConnection sendAsynchronousRequest:request queue:[[NSOperationQueue alloc] init] completionHandler:^(NSURLResponse *response, NSData *data, NSError *error){
//Write code you want to call when data is received,
//Like dismissing loading view and populating UI.
}];
Updated:
//Display alert view, before sending your request..
[alertview show];
//send first request
[NSURLConnection sendAsynchronousRequest:request1 queue:[[NSOperationQueue alloc] init] completionHandler:^(NSURLResponse *response, NSData *data, NSError *error){
//Write code you want to call when data is received,
//send second request
[NSURLConnection sendAsynchronousRequest:request2 queue:[[NSOperationQueue alloc] init] completionHandler:^(NSURLResponse *response, NSData *data, NSError *error){
//Write code you want to call when data is received,
//send third request
[NSURLConnection sendAsynchronousRequest:request3 queue:[[NSOperationQueue alloc] init] completionHandler:^(NSURLResponse *response, NSData *data, NSError *error){
//Write code you want to call when data is received,
//dismiss alert view on main thread
dispatch_async(getmainqueue, ^(void) {
// dismiss alert view...
});
}];
}];
}];

Answer 2

I have worked with Nuzhat Zari code, and I thank him for it, but also have experienced some issues with some core data operations between nested "sendAsynchronousRequest" (getting some weird thread and memory errors) so, my solution was unnest the calls to "sendAsynchronousRequest" and use some main thread variable validation.
#interface myMainThreadClass
#property (nonatomic,assign) NSInteger *currentAsyncTasks;
#end
#implementation
// Use init or viewDidLoad to make "currentAsyncTasks=0"!!
-(void)method
{
[self showLoadingAlert]; //or some ui update function
currentAsyncTasks++;
[NSURLConnection sendAsynchronousRequest:urlRequest queue:[[NSOperationQueue alloc] init] completionHandler:^(NSURLResponse *response, NSData *data, NSError *error){
//do something with data
dispatch_async(dispatch_get_main_queue(), ^(void) {
[self dismissAlertInFinalTask]
});
}];
currentAsyncTasks++;
[NSURLConnection sendAsynchronousRequest:urlRequest2 queue:[[NSOperationQueue alloc] init] completionHandler:^(NSURLResponse *response, NSData *data, NSError *error){
//do something with data
dispatch_async(dispatch_get_main_queue(), ^(void) {
[self dismissAlertInFinalTask]
});
}];
currentAsyncTasks++;
[NSURLConnection sendAsynchronousRequest:urlRequest3 queue:[[NSOperationQueue alloc] init] completionHandler:^(NSURLResponse *response, NSData *data, NSError *error){
//do something with data
dispatch_async(dispatch_get_main_queue(), ^(void) {
[self dismissAlertInFinalTask]
});
}];
}
-(void)dismissAlertInFinalTask
{
currentNetworkTasks--;
if (currentNetworkTasks == 0)
{
[self dismissLoadingAlert];//or some ui update function;
}
}
#end
I also want to know if someone has managed to do multiple request using NSURLConnection delegate NSURLConnectionDataDelegate and ui calls.