（一）分類中調用主類的實例方法或者類方法

場景：SDK中有個打點方法，但只有.h，沒有.m實現方法，現在需求是要對所有打點增加一個userName參數。方法一是在每個調用處都手動添加，這樣得改幾十處的代碼，并且以后也得顯性增加這個參數，明顯很麻煩；第二個是利用分類 覆蓋這個方法，在這個方法中統(tǒng)一加userName參數，追加完后再調用原類的方法，如此原來的調用不需要一一加參數修改。

#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)

//在分類中直接覆寫原類的方法
+ (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];
    //通過類對象獲取元類對象
    Class metaClass = object_getClass([LoadViewController class]);
    unsigned int count;
    Method *classMethods = class_copyMethodList(metaClass, &count); // 獲取所有類方法列表，metaClass換成[self class]就獲取所有實例方法列表
    for ( int i = count - 1 ; i >= 0; i--) { // 從后往前遍歷，因為分類方法被放在了主類方法前
        Method method = classMethods[I]; 
        SEL name = method_getName(method); // 方法選擇器
        IMP imp = method_getImplementation(method);  // 方法實現
        if (name == _cmd) { //等于當前方法
            //使用函數指針調用，(void *)只是告訴編譯器，不用報類型強轉的warning
            void(*function)(id, SEL, NSString *,NSString *,NSDictionary *,NSString *) = (void *)imp; 
            function([LoadViewController class],name,eventId,eventLabel,parameters,num);
            break;
        }
    }
    free(classMethods);
}

（二）class類結構體：

class-struct.png

看到里面有一個struct objc_method_list ** methodLists，這就是存儲該類所有方法的地方了。查找方法的時候并不是每次都去遍歷methodList的，而是先去cache中查，cache中存儲了最近常用的方法。

看一下objc_method_list這個結構體

struct-method-list.png

它有一個指向存儲廢棄方法列表的指針struct objc_method_list *obsolete，還有方法的個數int method_count，還有一個用于存儲方法的數組struct objc_method method_list[1]。其中數組的長度是可變的。

看一下objc_method這個結構體，

struct-objc_method.png

SEL method_name表示方法名，char *method_types表示參數及返回值類型，IMP method_imp表示指向方法實現的指針。

（三）、runtime 獲取類的屬性,實例方法,類方法和IMP交換等

導入：

#import <objc/message.h>

協(xié)議方法的獲取

- (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;
}

類屬性的獲取

- (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);
        //依次打印屬性名稱和屬性類型
        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);
}

實例方法的獲取

- (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(@"實例方法：%@",name);
    }
    free(methods);
}

類方法的獲取

- (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(@"類方法：%@",name);
    }
    free(classMethods);
}

方法交換 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