Show an AlertView, do parsing and dismiss AlertView - with GCD - ios

Question

I m very new to iOS, as stated in the question above; im trying to do these 3 simple step.
Show Alert view
Do parsing stuff
Dismiss Alert
I was looking for something like we have in android i.e Pre Execute, doInBackground and Post Execute().
This is what i have tried.
parserAlert = [[UIAlertView alloc] initWithTitle:#"Loading" message:#"Please Wait" delegate:nil cancelButtonTitle:#"Ok" otherButtonTitles:nil, nil];
[parserAlert show];
dispatch_queue_t queue = dispatch_queue_create("com.abc.testing", DISPATCH_QUEUE_SERIAL);
dispatch_sync(queue,^{
DBHandler *myDB= [[DBHandler alloc] init];
[myDB fetchResults];
dispatch_async(dispatch_get_main_queue(),^{
[parserAlert dismissWithClickedButtonIndex:0 animated:YES];
});
});
Below is the fetchResult method.
- (void) fetchResults
{
IParser *i = [[IParser alloc] init];
[i startParse];
AGParser *ag = [[AGParser alloc] init];
[ag startParse];
GParser *g = [[GParser alloc] init];
[g startParse];
HParser *h = [[HParser alloc] init];
[h startParse];
SParser *s = [[SParser alloc] init];
[s startParse];
}
This is startParse.
NSString *url = #"http://abcd.com/Service_URL/Service.asmx/GetNotes";
NSURL *nsUrl = [[NSURL alloc] initWithString:url];
NSURLRequest *request = [[NSURLRequest alloc] initWithURL:nsUrl];
NSURLConnection *con = [[NSURLConnection alloc] initWithRequest:request delegate:self];
responseData = [[NSMutableData alloc] init];
[con start];
When i run the above code, Alerview show and dismiss within a second. Adding logs on methods i observed that fetchresults method return immediately and alert view gets dismiss. However fetchResults associated threads(Connection methods, Parser methods) keep executing but alerview is dismissed.
I need a guideline how to block the code until all associated methods are finished.
Thanks for your time.

Answer 1

I know this is not the answer you want, but don't use an alert view for this. A nice way to cover for time-consuming activity to is to put up a UIActivityIndicatorView, or a view that contains one, and set it spinning:
http://www.apeth.com/iOSBook/ch25.html#_uiactivityindicatorview
You can also prevent user interaction while the time-consuming activity is happening, with the shared application object's beginIgnoring... (and turn that off with endIgnoring... when you're done). Obviously you can't do that, though, if the user is to be given a Cancel button. In that case, cover everything else with an invisible view (clear background color) whose userInteractionEnabled is YES, so that it eats any touches intended for anything other than the button.
Also, it is almost never the right answer to use dispatch_sync. Once you've frozen the interface in the way I've just described, you can just do your connections (asynchronous) and parsing (on a background thread) and then come back into the main thread to dismiss the activity indicator.
Finally, you're going to want to leave yourself a way out in case things go wrong. You could run an NSTimer, for example.
EDIT: And now for the actual answer to your actual question, i.e. why is my code not pausing even though I used dispatch_sync: it's because [[NSURLConnection alloc] initWithRequest:request delegate:self] returns immediately; the networking is in yet another background thread. So your startParse returns, your fetchResults returns, and meanwhile the networking continues and the NSURLConnection delegate methods are called some time later.

Answer 2

Here is the link what you are looking for MBProgressHUD
First alloc the MBProgressHUD instance of it in the viewDidLoad
MBProgressHUD *progressHUD = [[MBProgressHUD alloc] initWithView:self.view];
progress.delegate=self;
[progressHUD showWhileExecuting:#selector(performBackgroundTask) onTarget:self withObject:nil animated:YES]
and in the background method
-(void)performBackgroundTask
{
//Do some stuff
}
and soon as the task in the )performBackgroundTaskmethod is completed the Activity indicator shown in the MBProgressHUD will hidden and the delegate method called
-(void)hudWasHidden
{
//Do additional stuff after completion of background task
}
Hope it will help you.