（一）分类中调用主类的实例方法或者类方法

场景：SDK中有个打点方法，但只有.h，没有.m实现方法，现在需求是要对所有打点增加一个userName参数。方法一是在每个调用处都手动添加，这样得改几十处的代码，并且以后也得显性增加这个参数，明显很麻烦；第二个是利用分类 覆盖这个方法，在这个方法中统一加userName参数，追加完后再调用原类的方法，如此原来的调用不需要一一加参数修改。

#import "LoadViewController.h"

NS_ASSUME_NONNULL_BEGIN

@interface LoadViewController (Extension)
@end

NS_ASSUME_NONNULL_END

#import "LoadViewController+Extension.h"
#include <objc/runtime.h>
@implementation LoadViewController (Extension)

//在分类中直接覆写原类的方法
+ (void)setCustomEvent:(NSString *)eventId withLabel:(NSString *)eventLabel parameters:(NSDictionary *)parameters :(NSString*)num {
    NSMutableDictionary *mutableDic = [NSMutableDictionary dictionaryWithDictionary:parameters];
    [mutableDic setObject:@"42561324" forKey:@"userName"];
    parameters = [mutableDic copy];
    //通过类对象获取元类对象
    Class metaClass = object_getClass([LoadViewController class]);
    unsigned int count;
    Method *classMethods = class_copyMethodList(metaClass, &count); // 获取所有类方法列表，metaClass换成[self class]就获取所有实例方法列表
    for ( int i = count - 1 ; i >= 0; i--) { // 从后往前遍历，因为分类方法被放在了主类方法前
        Method method = classMethods[I]; 
        SEL name = method_getName(method); // 方法选择器
        IMP imp = method_getImplementation(method);  // 方法实现
        if (name == _cmd) { //等于当前方法
            //使用函数指针调用，(void *)只是告诉编译器，不用报类型强转的warning
            void(*function)(id, SEL, NSString *,NSString *,NSDictionary *,NSString *) = (void *)imp; 
            function([LoadViewController class],name,eventId,eventLabel,parameters,num);
            break;
        }
    }
    free(classMethods);
}

（二）class类结构体：

class-struct.png

看到里面有一个struct objc_method_list ** methodLists，这就是存储该类所有方法的地方了。查找方法的时候并不是每次都去遍历methodList的，而是先去cache中查，cache中存储了最近常用的方法。

看一下objc_method_list这个结构体

struct-method-list.png

它有一个指向存储废弃方法列表的指针struct objc_method_list *obsolete，还有方法的个数int method_count，还有一个用于存储方法的数组struct objc_method method_list[1]。其中数组的长度是可变的。

看一下objc_method这个结构体，

struct-objc_method.png

SEL method_name表示方法名，char *method_types表示参数及返回值类型，IMP method_imp表示指向方法实现的指针。

（三）、runtime 获取类的属性,实例方法,类方法和IMP交换等

导入：

#import <objc/message.h>

协议方法的获取

- (NSArray<NSString *> *)methodListWithProtocol:(Protocol *)protocol {
    unsigned int count = 0;
    NSMutableArray<NSString *> *methodList = @[].mutableCopy;
    struct objc_method_description *methods = protocol_copyMethodDescriptionList(protocol, YES, YES, &count);
    for (unsigned int i = 0; i < count; i++) {
        struct objc_method_description method = methods[I];
        NSString *name = NSStringFromSelector(method.name);
        [methodList addObject:name];
    }
    free(methods);
    return methodList;
}

类属性的获取

- (void)getIvarAndChange {
    NSLog(@"修改前:%@", self.name);
    unsigned int count = 0;
    Ivar *members = class_copyIvarList([self class], &count);
    for(int i = 0; i < count; i++) {
        Ivar ivar = members[I];
        const char *memberName = ivar_getName(ivar);
        const char *memberType = ivar_getTypeEncoding(ivar);
        //依次打印属性名称和属性类型
        NSLog(@"%s : %s", memberName, memberType);
        if(strcmp(memberName, "_name") == 0) {
            // 修改前
            NSString *name = (NSString *)object_getIvar(self, members[I]);
            NSLog(@"-name:%@", name);
            // 修改后
            object_setIvar(self, members[i], @"test");
            NSString *nameReset = (NSString *)object_getIvar(self, members[I]);
            NSLog(@"-nameReset:%@", nameReset);
            break;
        }
    }
    free(members);
    NSLog(@"修改后:%@", self.name);
}

实例方法的获取

- (void)getMethod {
    unsigned int count;
    Method *methods = class_copyMethodList([self class], &count);
    for (int i = 0; i < count; i++) {
        Method method = methods[I];
        SEL selector = method_getName(method);
        NSString *name = NSStringFromSelector(selector);
        NSLog(@"实例方法：%@",name);
    }
    free(methods);
}

类方法的获取

- (void)getClassMethod {
    Class metaClass = object_getClass([self class]);
    unsigned int count;
    Method *classMethods = class_copyMethodList(metaClass, &count);
    for (int i = 0; i < count; i++) {
        Method classMethod = classMethods[I];
        SEL selector = method_getName(classMethod);
        NSString *name = NSStringFromSelector(selector);
        NSLog(@"类方法：%@",name);
    }
    free(classMethods);
}

方法交换 method swizzled

+ (void)load{
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken,^{
        Class class = [self class];
        SEL originalSelector = @selector(viewDidAppear:);
        SEL mySwizzledSelector = @selector(myViewDidAppear:);
        
        Method originalMethod = class_getInstanceMethod(class, originalSelector);
        Method mySwizzledMethod = class_getInstanceMethod(class, mySwizzledSelector);
        
        BOOL addResult = class_addMethod(class, originalSelector, method_getImplementation(mySwizzledMethod), method_getTypeEncoding(mySwizzledMethod));
        if (addResult){
            class_replaceMethod(class, mySwizzledSelector, method_getImplementation(originalMethod), method_getTypeEncoding(originalMethod));
        }else{
            method_exchangeImplementations(originalMethod, mySwizzledMethod);
        }
    });
}

- (void)myViewDidAppear:(BOOL)animated
{
    [self myViewDidAppear:animated];
    NSLog(@"-----my view Did appear----,vc name = %@",[self class]);
}

method-and-implement-2.png