iOS开发Runtime 方法替换

通过#import <objc/runtime.h>我们可以找到：

/** 
 * Returns a specified instance method for a given class.
 * 
 * @param cls The class you want to inspect.
 * @param name The selector of the method you want to retrieve.
 * 
 * @return The method that corresponds to the implementation of the selector specified by 
 *  e name for the class specified by e cls, or c NULL if the specified class or its 
 *  superclasses do not contain an instance method with the specified selector.
 *
 * @note This function searches superclasses for implementations, whereas c class_copyMethodList does not.
 */
OBJC_EXPORT Method _Nullable
class_getInstanceMethod(Class _Nullable cls, SEL _Nonnull name)
    OBJC_AVAILABLE(10.0, 2.0, 9.0, 1.0, 2.0);

class_getInstanceMethod这个可以获取类的实例方法

#import <Foundation/Foundation.h>

NS_ASSUME_NONNULL_BEGIN

@interface RuntimeObjc : NSObject


-(void)runEg;
-(void)otherRunEg;

@end

#import "RuntimeObjc.h"
#import <objc/runtime.h>

@implementation RuntimeObjc

+(void)load{
    
    Method runEg = class_getInstanceMethod(self, @selector(runEg));
    Method otherRunEg = class_getInstanceMethod(self, @selector(otherRunEg));
　　//交换
    method_exchangeImplementations(runEg, otherRunEg);
}

-(void)runEg{
    NSLog(@"runEg");
}
-(void)otherRunEg{

　 NSLog(@"otherRunEg");

  [self otherRunEg];//已经做了置换 故调用的runEg

   
} 
@end

调用

    RuntimeObjc * objc = [[RuntimeObjc alloc]init];
    [objc runEg];

 打印：

2020-05-21 15:42:43.416766+0800 11111[35733:176260] otherRunEg
2020-05-21 15:42:43.416928+0800 11111[35733:176260] runEg