HUD is not working in iOS - ios

Question

I need to load some images from a JSON Object. When these images are loading, I need to show a HUD on my view. I tried to define a HUD like following,
Define HUD in viewDidLoad method
MBProgressHUD *hud = [MBProgressHUD showHUDAddedTo:self.view animated:YES];
hud.mode = MBProgressHUDModeIndeterminate;
hud.labelText = #"Loading Images";
[hud show:YES];
[hud showWhileExecuting:#selector(loadJSONData) onTarget:self withObject:nil animated:YES];
loadJSONData method
-(void)loadJSONData{
_myObject = [[NSMutableArray alloc] init];
NSData *jsonSource = [NSData dataWithContentsOfURL:[NSURL URLWithString:url]];
id jsonObjects = [NSJSONSerialization JSONObjectWithData:
jsonSource options:NSJSONReadingMutableContainers error:nil];
NSArray *dataDic = [jsonObjects objectForKey:#"data"];
for (NSDictionary *dicData in dataDic) {
Lawyer *l = [[Lawyer alloc] init];
dispatch_async(queue, ^{
NSString *imgUrl = [NSString stringWithFormat:#"myurl",l.imageUrl];
NSData *data = [NSData dataWithContentsOfURL:[NSURL URLWithString:imgUrl]];
UIImage *image = [UIImage imageWithData:data];
dispatch_async(dispatch_get_main_queue(), ^{
l.uiImage = image;
});
});
[_myObject addObject:[l initFromDictionary:dicData]];
}
}
My out put is showing the HUD for a second and disappeared. No data is loading. How do I fix this.
Thanks in Advance!

Answer 1

Your code is working as expected. loadJSONData performs an asynchronous request so the selector has actually finished executing. What you should do is show the HUD before the method loadJSONData and then hide it when the data has been received in:
dispatch_async(dispatch_get_main_queue(), ^{
l.uiImage = image;
[MBProgressHUD hideHUDForView:self.view animated:YES];
});
Although personally I would have a callback in loadJSONData and perform the HUD dismissal in a completion block.

Answer 2

Use this code :
MBProgressHUD *hud = [[MBProgressHUD alloc] initWithView: self.view];
[self.view addSubview: hud];
hud.labelText = #"Loading Images...";
[hud showAnimated:YES whileExecutingBlock:^{
[self loadJSONData];
} completionBlock:^{
// Refresh UI
}];
But make sure , as whileExecutingBlock using thread you have to make all UI change on main thread.