用类别覆盖方法时如何调用原始实现？

发布于 2024-10-05 04:08:23 字数 436 浏览 11 评论 0原文

我试图弄清楚事情到底是如何运作的。所以我想当我使用类别覆盖某些方法时，我会得到有趣的 NSLogs。

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

super 和 self 在这里不起作用。有没有办法调用 -hitTest:withEvent: 的原始实现？我想要的是每次在 UIView 上调用 -hitTest:withEvent: 时生成一个 NSLog。

仅供个人学习之用。我想看看事件传递的实际情况。

原文

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

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.

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

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凉世弥音 2024-10-12 04:08:23

您可以这样做，但不能使用类别。类别取代了方法。（警告，汽车类比）如果你有一辆汽车，你毁掉那辆车并换上一辆新车，你还能使用旧车吗？不，因为它已经消失了，不再存在了。与类别相同。

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:withEvent 的实现：和bogusHitTest:withEvent:。这样，当代码调用 hitTest:withEvent: 时，它将执行最初为 bogusHitTest:withEvent: 编写的代码。然后，您可以让该代码调用 bogusHitTest:withEvent:，它将执行原始实现。

因此，伪造的方法将如下所示：

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

交换方法的代码将类似于：

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

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.

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.

So the bogus method would look like:

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

The code to swap the methods would be something along the lines of:

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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