多个情节提要：我应该使用单例模式来缓存它们吗？

我在我的应用中使用了多个故事板，这被认为是一种很好的做法。例如，从我在 Main.storyboard 中的 FooViewController 中，点击一个按钮时，我将跳转到另一个 BarViewController 在 Secondary.storyboard 中以编程方式定义。

I'm using multiple storyboards in my app, which is considered as good practice. For example, from my FooViewController in Main.storyboard, when a button is tapped, I'll jump to another BarViewController defined in Secondary.storyboard programmatically.

故事板和视图控制器在单独的文件中实现，例如 Storyboards ，如下所示：

Transitions among storyboards and view controllers are implemented in a separate file, e.g. Storyboards, like the following:

// in Storyboards.m
@implementation Storyboards

+ (id)instantiateBarViewController {
    UIStoryboard *storyboard = [UIStoryboard storyboardWithName:@"Secondary" bundle:nil];
    return [storyboard instantiateViewControllerWithIdentifier:@"BarViewController"];
}

@end

然后在 FooViewController ，我是这样做的：

Then in FooViewController, I did this:

// in FooViewController.m
- (IBAction)someButtonTapped:(id)sender {
    BarViewController *controller = [Storyboards instantiateBarViewController];
    [self.navigationController pushViewController:controller animated:YES];
}

这很好用。但是我的问题是：

This works just fine. But my questions are:

1. 是否有必要缓存情节提要实例，以便每次 instantiateBarViewController 被调用，我不需要重新创建情节提要吗？


2. 如果是，我也应该缓存 BarViewController 吗？

1. Is it necessary to cache the storyboard instance, so that everytime instantiateBarViewController is invoked, I do not need to re-create the storyboard?
2. If yes, should I cache BarViewController too?

要缓存故事板（和视图控制器），我可以使用以下代码：

To cache the storyboard (and the view controller), I could use code as the following:

// in Storyboards.m
@implementation Storyboards

+ (id)instantiateBarViewController {
    static UIViewController *barViewController = nil;  // Shared view controller.
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        UIStoryboard *storyboard = [self secondaryStoryboard];
        barViewController = [storyboard instantiateViewControllerWithIdentifier:@"BarViewController"];
    });
    return barViewController;
}

+ (UIStoryboard *)secondaryStoryboard {
    static UIStoryboard *storyboard = nil;  // Shared storyboard.
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        storyboard = [UIStoryboard storyboardWithName:@"Secondary" bundle:nil];
    });
    return storyboard;
}

@end

谢谢！