objective-c - Objective-C Method Swizzling 示例不起作用

Question

我想尝试 Method Swizzling 以清楚地了解它是如何工作的。查看此代码： http: //nshipster.com/method-swizzling/。我创建了一个类和一个类别，这是代码

#import <Foundation/Foundation.h>

@interface CustomClass : NSObject

-(void) originalMethod;

@end

类的实现

#import "CustomClass.h"

@implementation CustomClass

-(id) init {
    self = [super init];
    return self;
}

-(void) originalMethod {
    NSLog(@"I'm the original method");
}

@end

类别标题：

#import "CustomClass.h"

@interface CustomClass (CustomCategory)

-(void) newMethod;

@end

类别实施

#import "CustomClass+CustomCategory.h"
#include <objc/runtime.h>

@implementation CustomClass (CustomCategory)

-(void) newMethod {
    [self newMethod];
    NSLog(@"I'm the new method");
}

+(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(originalMethod:);
        SEL swizzledSelector = @selector(newMethod:);

        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);
        }
    });
}

@end

这是主要的：

#import <Foundation/Foundation.h>
#import "CustomClass.h"
#import "CustomClass+CustomCategory.h"

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        CustomClass *cc = [[CustomClass alloc] init];
        [cc newMethod];
    }
    return 0;
}

当我打电话时[cc newMethod]，我得到了无限循环，根据我链接的文章，这不应该发生。我在这段代码中看不到错误。

Answer 1

问题出在语法上，而不是

SEL originalSelector = @selector(originalMethod:);
SEL swizzledSelector = @selector(newMethod:);

我应该写：

SEL originalSelector = @selector(originalMethod);
SEL swizzledSelector = @selector(newMethod);

xCode 只给了我一个警告，所以我认为选择器名称没有错。

Answer 2

看起来你在调配类方法：

Class class = [self class];

指向+load上下文中的元类，尝试明确指定它，即

Class class = [CustomClass class];
// or
Class class = self;

另外，@bbum 说了什么

Answer 3

    class_replaceMethod(class,
                        swizzledSelector,
                        method_getImplementation(originalMethod),
                        method_getTypeEncoding(originalMethod));

不method_getImplementation(originalMethod)应该swizzledMethod吗？

Answer 4

1. 语法错误，运行时会发送不同的消息。

   SEL originalSelector = @selector(originalMethod);
   SEL swizzledSelector = @selector(newMethod);
   

2. 如果第一种方法没有效果。试试看：

   BOOL didAddMethod =
   class_addMethod(class, originalSelector,
                   method_getImplementation(swizzledMethod),
                   method_getTypeEncoding(swizzledMethod));
   
   if (didAddMethod) {
       method_exchangeImplementations(originalMethod, swizzledMethod);
   
   }
   

交换实施可能会产生的影响。