当子类重写方法时，我们如何在编译时确保调用超类的方法实现？ [英] When a subclass overrides a method, how can we ensure at compile time that the superclass's method implementation is called?

问题描述

经典的例子是：

- (void)viewDidLoad {
    [super viewDidLoad]; // Subclasses sometimes forget this line

    // Subclass's implementation goes here
}

有什么方法可以确保在编译时 UIViewController 子类总是调用 [super viewDidLoad] 时他们覆盖 [UIViewController viewDidLoad] ？

What are some ways to ensure at compile time that UIViewController subclasses always call [super viewDidLoad] when they override [UIViewController viewDidLoad]?

推荐答案

如果我们在说话关于自定义类，您可以将以下内容添加到超类的方法声明中：

If we're talking about custom classes, you can add the following to your superclass's method declaration:

__attribute__((objc_requires_super));

---

如果你想确保所有的 UIViewController 子类调用类似 [super viewDidLoad]; 的方法，你可以继承 UIViewController 类似这样的事情：

---

And if you want to ensure that all of your UIViewController subclasses call a method like [super viewDidLoad];, you could subclass UIViewController something like this:

@interface BaseViewController : UIViewController

- (void)viewDidLoad __attribute__((objc_requires_super));

// per Scott's excellent comment:
- (void)viewWillAppear:(BOOL)animated NS_REQUIRES_SUPER;

@end

---

---

@implementation BaseViewController

- (void)viewDidLoad {
    [super viewDidLoad];
}

- (void)viewWillAppear:(BOOL)animated {
    [super viewWillAppear:animated];
}

@end

然后只是子类 BaseViewController 整个项目，而不是继承 UIViewController 。

And then just subclass BaseViewController throughout your project, rather than subclassing UIViewController.

任何实现 viewDidLoad 的 BaseViewController 的子类，并且不调用 [super viewDidLoad]; （反过来调用 UIViewController 的 viewDidLoad ）会发出警告。

Any subclass of BaseViewController which implements viewDidLoad and does not call [super viewDidLoad]; (which in turn calls UIViewController's viewDidLoad) will throw a warning.

编辑：我已经编辑了答案，包括 NS_REQUIRES_SUPER 的示例，每个斯科特的出色评论。这两个示例（ viewDidLoad 和 viewWillAppear：）在功能上是等效的。虽然我想象 NS_REQUIRES_SUPER 可能会为你自动完成。我将来可能会开始使用这个宏。

I've edited the answer to include an example of NS_REQUIRES_SUPER, per Scott's excellent comment. The two examples (viewDidLoad and viewWillAppear:) are functionally equivalent. Though I imagine NS_REQUIRES_SUPER probably will autocomplete for you. I'll likely begin using this macro myself in the future.

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