Question

我想尝试使用Method Swizzling清楚地了解它是如何工作的。看看这段代码：http://nshipster.com/method-swizzling/。我创建了一个类和一个类别，这里是代码

#import <Foundation/Foundation.h>

@interface CustomClass : NSObject

-(void) originalMethod;

@end

课程的实施

#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;
}

当我打电话给[cc newMethod]时，我得到了无限循环，这根据我链接的文章不应该发生。我无法在此代码中看到错误。

Answer 1

问题在于语法，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，所以我没想到选择器名称是错误的。

Answer 2

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

不应method_getImplementation(originalMethod)为swizzledMethod？

Answer 3

好像你在调整类方法：

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说什么

Answer 4

语法错误，运行时会发送不同的消息。

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

if (didAddMethod) {
    method_exchangeImplementations(originalMethod, swizzledMethod);

}

如果第一种方式无效。试试吧：
```
File.separator
```

交换实施可能会有效。

Objective-C方法Swizzling示例不起作用

4 个答案: