objective-c - Objective-C 中的方法调配

Question

我读了一篇 article about "Method Swizzling in Objective-C" .本文中“Method Swizzing”的意思是交换两个方法的实现。示例如下所示:

- (void) logged_viewDidAppear:(BOOL)animated {
    [self logged_viewDidAppear:animated];
    NSLog(@"logged view did appear for %@", [self class]);
}
+ (void)load {
    static dispatch_once_t once_token;
    dispatch_once(&once_token,  ^{
        SEL viewWillAppearSelector = @selector(viewDidAppear:);
        SEL viewWillAppearLoggerSelector = @selector(logged_viewDidAppear:);
        Method originalMethod = class_getInstanceMethod(self, viewWillAppearSelector);
        Method extendedMethod = class_getInstanceMethod(self, viewWillAppearLoggerSelector);
        method_exchangeImplementations(originalMethod, extendedMethod);
    });
}
- (void) logged_viewDidAppear:(BOOL)animated {
    [self logged_viewDidAppear:animated];
    NSLog(@"logged view did appear for %@", [self class]);
}

在文章中，有一句话是

It may seem this this method makes a nonsensical recursive call to itself, but it won’t actually be doing that after we swizzle it.

但是我不是很清楚这个说法，是不是意味着当我们这样写代码的时候:

[self viewDidAppear], 

因为它的实现变成了“logged_viewDidAppear”，所以程序转到方法“logged_viewDidAppear”，在那个方法中我们可以看到，第一行是[self logged_viewDidAppear:animated];出于同样的原因，该方法变为“viewDidAppear”。我的话对吗？

Answer 1

是的。当调用 viewDidAppear 时，它实际上会在运行时调配到 logged_viewDidAppear 的实现，调用 logged_viewDidApear 也是如此。

检查这个:http://nshipster.com/method-swizzling/和这个 https://www.bignerdranch.com/blog/inside-the-bracket-part-7-runtime-machinations/