__block bool theResult;
    [self.mbProgressHUD showAnimated:YES whileExecutingBlock:^{
      theResult = [someClass someMethodThatReturnsTRUEorFALSE];
    } completionBlock:^{
      [self.mbProgressHUD removeFromSuperview];
      if (theResult) {
        dispatch_async(dispatch_get_main_queue(), ^{
          UIAlertView *theAlert....
          [theAlert show];
        });
      };
    }];