UI issues while using blocks

Question

I am using MBProgressHUD to display a loading indicator on my app. When i want to change something at UI or i open a new screen inside block, i only see a blank white screen. Does anyone has an idea what am i missing in my code?

-(void)doSomething:(id)sender
{
HUD = [[MBProgressHUD alloc] initWithView:self.view];
[self.view addSubview:HUD];

HUD.delegate = self;
HUD.labelText = @"Please wait";
[HUD showAnimated:YES whileExecutingBlock:^{
NSDictionary* dictReturn = [ServerApi getItemDetails::itemId userId:userId;
NewScreenController* vc = [[NewScreenController alloc]init];
[self presentViewController:vc animated:YES completion:nil];
}];    
}

Answer 1

MBProgressHUD doesn't execute the block in the main thread. That's why you shouldn't change UI there at all.

You should use the method with a completionBlock instead.

- (void)doSomething:(id)sender {
     HUD = [[MBProgressHUD alloc] initWithView:self.view];
     [self.view addSubview:HUD];

     HUD.delegate = self;
     HUD.labelText = @"Please wait";

     dispatch_block_t executionBlock = ^{
        self.dictReturn = [ServerApi getItemDetails:itemId userId:userId];
     };

     void (^completionBlock)() = ^{
         NewScreenController *vc = [[NewScreenController alloc] init];
         [self presentViewController:vc animated:YES completion:nil];
     };

     [HUD showAnimated:YES
   whileExecutingBlock:executionBlock
       completionBlock:completionBlock];
}