Question

我正在学习方法调配。我理解一切，除非这样做，否则我会玩它：

#import <objc/runtime.h>

@implementation UIViewController (Tracking)

+ (void)load {
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        Class class = [self class];

        // When swizzling a class method, use the following:
        // Class class = object_getClass((id)self);

        SEL originalSelector = @selector(viewWillAppear:);
        SEL swizzledSelector = @selector(xxx_viewWillAppear:);

        Method originalMethod = class_getInstanceMethod(class, originalSelector);
        Method swizzledMethod = class_getInstanceMethod(class, swizzledSelector);

        BOOL didAddMethod =
            class_addMethod(class,
                originalSelector,
                method_getImplementation(swizzledMethod),
                method_getTypeEncoding(swizzledMethod));

        if (didAddMethod) {
            class_replaceMethod(class,
                swizzledSelector,
                method_getImplementation(originalMethod),
                method_getTypeEncoding(originalMethod));
        } else {
            method_exchangeImplementations(originalMethod, swizzledMethod);
        }
    });
}

#pragma mark - Method Swizzling

- (void)xxx_viewWillAppear:(BOOL)animated {
    [self xxx_viewWillAppear:animated];
    NSLog(@"viewWillAppear: %@", self);
}

@end

来源NSHipster。

在调用：

时，Objective C如何再次解析对原始函数的调用

[self xxx_viewWillAppear:animated];

因为我们在调度表中调整了viewWillAppear所以这是如何完成的？我认为它会打电话给自己，但它不是。任何人都可以向我解释这最后一块拼图吗？

Answer 1

调用

时

[self xxx_viewWillAppear:animated];

你不再称呼自己，而是为

提供的原始实现

viewWillAppear:animated

当你调整它们时，这两个实现“切换到了位置”。

方法调整为什么没有递归

1 个答案: