如何在覆盖带有类别的方法时调用原始实现？ [英] How to call original implementation when overwriting a method with a category?

问题描述

我试着弄清楚事情是如何运作的。所以我想当我使用类别覆盖某些方法时，我会得到有趣的NSLog。

I try to figure out how things really work. So I thought when I would overwrite certain methods using categories, I would get interesting NSLogs.

@implementation UIView(Learning)
- (UIView *)hitTest:(CGPoint)point withEvent:(UIEvent *)event {
    NSLog(@"-hitTest:withEvent: event=%@", event);
    return [self hitTest:point withEvent:event];
}
@end

超级和自我在这里不起作用。有没有办法调用-hitTest的原始实现：withEvent：？我想要的是NSLog每次-hitTest：withEvent：在UIView上调用。

super and self don't work here. Is there a way to call the original implementation of -hitTest:withEvent:? What I want is an NSLog every time -hitTest:withEvent: is called on an UIView.

它仅用于个人学习目的。我希望看到事件交付的实际效果。

It's just for personal learning purposes. I want to see the event delivery in action.

推荐答案

您可以这样做，但不能使用类别。类别替换方法。 （警告，汽车比喻）如果你有一辆汽车，然后你摧毁那辆汽车并换上一辆新车，你还能使用旧车吗？不，因为它消失了，不再存在了。与类别相同。

You can do it, but not using a category. A category replaces a method. (Warning, car analogy) If you have a car, and you destroy that car and replace it with a new car, can you still use the old car? No, because it is gone and does not exist anymore. The same with categories.

您可以做的是使用Objective-C运行时在运行时以不同的名称添加方法（例如， bogusHitTest：withEvent：），然后交换 hitTest的实现：withEvent：和 bogusHitTest：withEvent：。这样当代码调用 hitTest：withEvent：时，它将执行最初为 bogusHitTest编写的代码：withEvent：。然后，您可以让代码调用 bogusHitTest：withEvent：，这将执行原始实现。

What you could do is use the Objective-C runtime to add the method under a different name at runtime (say, "bogusHitTest:withEvent:"), then swap the implementations of hitTest:withEvent: and bogusHitTest:withEvent:. That way when the code calls hitTest:withEvent:, it's going to execute the code that was originally written for bogusHitTest:withEvent:. You can then have that code invoke bogusHitTest:withEvent:, which will execute the original implementation.

所以伪造方法如下：

- (UIView *) bogusHitTest:(CGPoint)point withEvent:(UIEvent *)event {
  NSLog(@"executing: %@", NSStringFromSelector(_cmd));
  return [self bogusHitTest:point withEvent:event];
}

交换方法的代码将是：

Method bogusHitTest = class_getInstanceMethod([UIView class], @selector(bogusHitTest:withEvent:));
Method hitTest = class_getInstanceMethod([UIView class], @selector(hitTest:withEvent:));
method_exchangeImplementations(bogusHitTest, hitTest);

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