Initialize UITableview with Contents from XML but can't show progress with UIAlertview

Question

I am writing an app, which is getting data from the net using XML. It is a master-detail-app which is fetching data for the master-table and after selecting one item from the master-Table it fills the data for the detailview(s) using another network-access.

I would like to present an alert in order to show the user that the app is busy accessing the net or busy calculating. So I would present the view from the UIAlertController before the calculation / network access starts and dismiss the view when the activity has completed

Problem is: I don't know where to put this call to show / dismiss the UIAlertcontroller view.

Putting the activity code into ViewWillAppear shows and dismisses the alertview BEFORE the network-access... Putting everything into ViewDidLoad seems not the way to go.

- (void) viewWillAppear:(BOOL)animated
{
    UIAlertController *alert = [UIAlertController alertControllerWithTitle:@"Working"
                                                                   message:@"Working on it"
                                                            preferredStyle:UIAlertControllerStyleAlert];

    self.objects = [[NSMutableArray alloc] init];
    self.navigationItem.backBarButtonItem = [[UIBarButtonItem alloc]initWithTitle:@"Accounts"
                                                                            style:UIBarButtonItemStylePlain
                                                                           target:nil
                                                                           action:nil];

    NSURL *url;
    if ([self getSession])
    {
        NSMutableString *URLstring = [NSMutableString stringWithString:@"https://XXXXXXXXXXXXXXX.xml?session="];

        [self presentViewController:alert animated:YES completion:nil];
        [URLstring appendString:[[DataStore getData]SessionString]];

        url = [NSURL URLWithString:URLstring];
        self.myXXXXXXParserAlleKontenXMLDelegate = [[KontenParserDelegate alloc] init];
        self.xmlParser = [[NSXMLParser alloc] initWithContentsOfURL:url];
        self.xmlParser.delegate = self.myfxbookParserAlleKontenXMLDelegate;

        if ([self.xmlParser parse])
        {
            [self.objects removeAllObjects];

            for(int i=0; i< [self.XXXXXXXXXrAlleKontenXMLDelegate.allAccounts count];i++)
            {
                [self.objects addObject : [self.myfxbookParserAlleKontenXMLDelegate.allAccounts objectAtIndex:i]];
            }
            NSSortDescriptor *sort = [[NSSortDescriptor alloc] initWithKey: @"name" ascending: YES];
            [self.objects sortUsingDescriptors:@[sort]];

            [self.tableView reloadData];
            [self dismissViewControllerAnimated:YES completion:nil];
            // Do any additional setup after loading the view, typically from a nib.
        }
    }
}

Added After some discussions I added some new framework "SVProgressHUD" and entered the following code into "ViewWillAppear" where [self parserstuff] contains all the XML parsing..

[SVProgressHUD show];
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
   [self parserstuff];
dispatch_async(dispatch_get_main_queue(), ^{
      [SVProgressHUD dismiss];
    });
});

This leaves me with a HUD-Display showing up while parsing XML but the resulting Tableview does not show data but is empty... After switching to DISPATCH_SYNC it works.

Solution would be

1) Put code in ViewDidLoad 2) encapsulate Code between "SVProgressHUD show" and "dismiss" with dispatch_async

as in

dispatch_async(dispatch_get_main_queue(), ^{
    [SVProgressHUD show];
    [self parserstuff];
    [self fillComparatorParameters:nil];
    [self.tableView reloadData];
    [SVProgressHUD dismiss];
   // }];
});