How to set text shadow to the text in UITabBar?

textShadow_in_UITabBar.m

//...

  [self.tabBarController.tabBar.items enumerateObjectsUsingBlock:^(UITabBarItem *aTabBarItem, NSUInteger idx, BOOL *stop) {
    NSString *selectedImageName = [NSString stringWithFormat:@"tab_icon%d_27x27_selected", idx+1];
    NSString *unselectedImageName = [NSString stringWithFormat:@"tab_icon%d_27x27", idx+1];
    [aTabBarItem setFinishedSelectedImage:[UIImage imageNamed:selectedImageName] 
              withFinishedUnselectedImage:[UIImage imageNamed:unselectedImageName]];
    
    [aTabBarItem setTitleTextAttributes:[NSDictionary dictionaryWithObjectsAndKeys:
                                         [[UIColor blackColor] colorWithAlphaComponent:0.5], UITextAttributeTextShadowColor, 
                                         [NSValue valueWithCGSize:CGSizeMake(0, -1)], UITextAttributeTextShadowOffset, 
                                         nil] 
                               forState:UIControlStateNormal];
    
  }];

//...