方法替换：－实现拦截功能

顾名思义，就用一个方法替换一个方法的意思：

直接上代码，我自己看英文，也不翻译了，想了解的可以去看文档
点击这里直接看英文文档 

  另外还有好多其他的扩展

在方法替换的过程中，我们可以用分类扩展方法来替换，也可以在本类方法之间的替换

首先声明交换方法

#import </usr/include/objc/objc-class.h>

Void MethodSwizzle(Class aClass, SEL orig_sel, SEL alt_sel)实现功能：void  MethodSwizzle(Class aClass, SEL orig_sel, SEL alt_sel) { Method orig_method = nil, alt_method = nil;    // First, look for the methods    orig_method = class_getInstanceMethod(aClass, orig_sel); alt_method = class_getInstanceMethod(aClass, alt_sel);    // If both are found, swizzle them if ((orig_method != nil) && (alt_method != nil))        {        char *temp1; IMP temp2; temp1 = orig_method->method_types;        orig_method->method_types = alt_method->method_types;        alt_method->method_types = temp1;        temp2 = orig_method->method_imp;        orig_method->method_imp = alt_method->method_imp;        alt_method->method_imp = temp2;        }}

当然我们也有自己的方法来实现交换：
void Swizzle(Class c, SEL orig, SEL _new)
{
    MethodorigMethod = class_getInstanceMethod(c, orig);
    MethodnewMethod = class_getInstanceMethod(c, _new);
   if(class_addMethod(c, orig, method_getImplementation(newMethod),method_getTypeEncoding(newMethod)))
       class_replaceMethod(c, _new, method_getImplementation(origMethod),method_getTypeEncoding(origMethod));
    else
      method_exchangeImplementations(origMethod, newMethod);
}

在工程中，经常使用方法拦截之后（方法替换）之后，我们再次把方法替换回来，为了不影响其他模块使用这个系统功能。

可以定义成一个宏：
#define METHODCALLBACK(taget){\
NSString *__Name=NSStringFromSelector(_cmd);\
NSString *_selectorName=[@"__Inv_"stringByAppendingString:__Name];\
Swizzle([self class], NSSelectorFromString(_selectorName),NSSelectorFromString(__Name));\
taget;\
Swizzle([self class], NSSelectorFromString(__Name),NSSelectorFromString(_selectorName));\
}

原型是：
METHODCALLBACK(taget){
NSString *__Name=NSStringFromSelector(_cmd);
NSString *_selectorName=[@"__Inv_"stringByAppendingString:__Name];
Swizzle([self class], NSSelectorFromString(_selectorName),NSSelectorFromString(__Name));
taget;
Swizzle([self class], NSSelectorFromString(__Name),NSSelectorFromString(_selectorName));
}