runtime

runtime介绍

• Objective-C是一门动态的编程语言，跟C、C++等语言有着很大的不同(编写代码 -> 编译链接 -> 运行)
• Objective-C的动态性是由Runtime API来支撑的
• Runtime API提供的接口基本都是C语言的，源码由C\C++\汇编语言编写

isa详解

• 在arm64架构之前，isa就是一个普通的指针，存储着Class、Meta-Class对象的内存地址
• 从arm64架构开始，对isa进行了优化，变成了一个共用体（union）结构，还使用位域来存储更多的信息

@interface TGPerson : NSObject
- (void)setTall:(BOOL)tall;
- (void)setRich:(BOOL)rich;
- (void)setHandsome:(BOOL)handsome;
- (void)setThin:(BOOL)thin;

- (BOOL)isTall;
- (BOOL)isRich;
- (BOOL)isHandsome;
- (BOOL)isThin;

@end


#import "TGPerson.h"
/**
 把值存在不同的二进制位上，通过掩码来获取，共同体只开辟一份内存，减少内存的分配
 */
#define TGTallMask (1<<0)
#define TGRichMask (1<<1)
#define TGHandsomeMask (1<<2)
#define TGThinMask (1<<3)

@interface TGPerson ()
{
    union {
        char bits;
        
        struct {
            char tall : 1;
            char rich : 1;
            char handsome : 1;
            char thin : 1;
        }; //结构体只是增加可读性
    } _tallRichHandsome;
}
@end

@implementation TGPerson

- (void)setTall:(BOOL)tall
{
    if (tall) {
        _tallRichHandsome.bits |= TGTallMask;
    } else {
        _tallRichHandsome.bits &= ~TGTallMask;// ~取反
    }
}

- (BOOL)isTall
{
    return !!(_tallRichHandsome.bits & TGTallMask);// !! 转成布尔类型
}

- (void)setRich:(BOOL)rich
{
    if (rich) {
        _tallRichHandsome.bits |= TGRichMask;
    } else {
        _tallRichHandsome.bits &= ~TGRichMask;
    }
}

- (BOOL)isRich
{
    return !!(_tallRichHandsome.bits & TGRichMask);
}

- (void)setHandsome:(BOOL)handsome
{
    if (handsome) {
        _tallRichHandsome.bits |= TGHandsomeMask;
    } else {
        _tallRichHandsome.bits &= ~TGHandsomeMask;
    }
}

- (BOOL)isHandsome
{
    return !!(_tallRichHandsome.bits & TGHandsomeMask);
}


- (void)setThin:(BOOL)thin
{
    if (thin) {
        _tallRichHandsome.bits |= TGThinMask;
    } else {
        _tallRichHandsome.bits &= ~TGThinMask;
    }
}

- (BOOL)isThin
{
    return !!(_tallRichHandsome.bits & TGThinMask);
}

@end


/********************* 写入、读取 **************************/
int main(int argc, const char * argv[]) {
    @autoreleasepool {
        
        TGPerson *person = [[TGPerson alloc] init];
        person.thin = YES;
        person.rich = YES;
        person.handsome = NO;
        
        NSLog(@"thin:%d rich:%d hansome:%d", person.isThin, person.isRich, person.isHandsome);
    }
    return 0;
}

isa内部结构.png

• nonpointer
  0，代表普通的指针，存储着Class、Meta-Class对象的内存地址
  1，代表优化过，使用位域存储更多的信息

• has_assoc
  是否有设置过关联对象，如果没有，释放时会更快

• has_cxx_dtor
  是否有C++的析构函数（.cxx_destruct），如果没有，释放时会更快

• shiftcls
  存储着Class、Meta-Class对象的内存地址信息

• magic
  用于在调试时分辨对象是否未完成初始化

• weakly_referenced
  是否有被弱引用指向过，如果没有，释放时会更快

• deallocating
  对象是否正在释放

• extra_rc
  里面存储的值是引用计数器减1

• has_sidetable_rc
  引用计数器是否过大无法存储在isa中
  如果为1，那么引用计数会存储在一个叫SideTable的类的属性中

oc对象销毁过程中会调用下面函数
/****************************************************** 
* objc_destructInstance
* Destroys an instance without freeing memory. 
* Calls C++ destructors.
* Calls ARC ivar cleanup.
* Removes associative references.
* Returns `obj`. Does nothing if `obj` is nil.
*********************************************************/
void *objc_destructInstance(id obj) 
{
    if (obj) {
        // Read all of the flags at once for performance.
        bool cxx = obj->hasCxxDtor();
        bool assoc = obj->hasAssociatedObjects();

        // This order is important.
        if (cxx) object_cxxDestruct(obj);
        if (assoc) _object_remove_assocations(obj);
        obj->clearDeallocating();
    }

    return obj;
}

#import "ViewController.h"

typedef enum {
//    TGOptionsNone = 0,    // 0b0000
    TGOptionsOne = 1<<0,   // 0b0001
    TGOptionsTwo = 1<<1,   // 0b0010
    TGOptionsThree = 1<<2, // 0b0100
    TGOptionsFour = 1<<3   // 0b1000
} TGOptions;

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    [self setOptions: TGOptionsOne | TGOptionsFour];
}

- (void)setOptions:(TGOptions)options
{
    if (options & TGOptionsOne) {
        NSLog(@"包含了TGOptionsOne");
    }
    if (options & TGOptionsTwo) {
        NSLog(@"包含了TGOptionsTwo");
    }
    if (options & TGOptionsThree) {
        NSLog(@"包含了TGOptionsThree");
    }
    if (options & TGOptionsFour) {
        NSLog(@"包含了TGOptionsFour");
    }
}

class结构

class内部结构

class_ro_t

class_ro_t里面的baseMethodList、baseProtocols、ivars、baseProperties是一维数组，是只读的，包含了类的初始内容,一开始就有

class_ro_t.png

class_rw_t

class_rw_t里面的methods、properties、protocols是二维数组，是可读可写的，包含了类的初始内容、分类的内容,一开始没有

class_rw_t

method_t

• method_t是对方法\函数的封装

struct method_t {
    SEL name; //函数名
    const char *types; //编码(返回值类型、参数类型)
    MethodListIMP imp;//指向函数的指针(函数地址)
}

• IMP代表函数的具体实现

  
  IMP.png

• SEL代表方法\函数名，一般叫做选择器，底层结构跟char *类似
  • 可以通过@selector()和sel_registerName()获得
  • 可以通过sel_getName()和NSStringFromSelector()转成字符串

  • 不同类中相同名字的方法，所对应的方法选择器是相同的

    
    SEL.png

types包含了函数返回值、参数编码的字符串

types methods

@interface TGPerson : NSObject

// "i24@0:8i16f20"
// 0id 8SEL 16int 20float  == 24
/**
* i表示返回值类型 24表示 参数总共占多少字节数 
*@表示第一个参数是id类型 从第0个字节开始 
*：表示参数是SEL 从第8个字节开始
* i表示参数是int类型 从20字节开始 
*f表示参数是 float类型 从20字节开始
*/
- (int)test:(int)age height:(float)height;
@end

encoding.png type-encoding.png

static Class realizeClass(Class cls)
{
    runtimeLock.assertLocked();

    const class_ro_t *ro;
    class_rw_t *rw;
    Class supercls;
    Class metacls;
    bool isMeta;

    if (!cls) return nil;
    if (cls->isRealized()) return cls;
    assert(cls == remapClass(cls));

    // fixme verify class is not in an un-dlopened part of the shared cache?

    ro = (const class_ro_t *)cls->data();//ro一开始就有
    if (ro->flags & RO_FUTURE) {
        // This was a future class. rw data is already allocated.
        rw = cls->data();
        ro = cls->data()->ro;
        cls->changeInfo(RW_REALIZED|RW_REALIZING, RW_FUTURE);
    } else {
        // Normal class. Allocate writeable class data.
        rw = (class_rw_t *)calloc(sizeof(class_rw_t), 1);//rw一开始没有
        rw->ro = ro;
        rw->flags = RW_REALIZED|RW_REALIZING;
        cls->setData(rw);
    }
    // Realize superclass and metaclass, if they aren't already.
    // This needs to be done after RW_REALIZED is set above, for root classes.
    // This needs to be done after class index is chosen, for root metaclasses.
    supercls = realizeClass(remapClass(cls->superclass));
    metacls = realizeClass(remapClass(cls->ISA()));
    // Update superclass and metaclass in case of remapping
    cls->superclass = supercls;
    cls->initClassIsa(metacls);

    // Reconcile instance variable offsets / layout.
    // This may reallocate class_ro_t, updating our ro variable.
    if (supercls  &&  !isMeta) reconcileInstanceVariables(cls, supercls, ro);

    // Set fastInstanceSize if it wasn't set already.
    cls->setInstanceSize(ro->instanceSize);

    // Copy some flags from ro to rw
    if (ro->flags & RO_HAS_CXX_STRUCTORS) {
        cls->setHasCxxDtor();
        if (! (ro->flags & RO_HAS_CXX_DTOR_ONLY)) {
            cls->setHasCxxCtor();
        }
    }

    // Connect this class to its superclass's subclass lists
    if (supercls) {
        addSubclass(supercls, cls);
    } else {
        addRootClass(cls);
    }
    methodizeClass(cls);
    return cls;
}

方法缓存

Class内部结构中有个方法缓存（cache_t），用散列表（哈希表）来缓存曾经调用过的方法，可以提高方法的查找速度
缓存查找

内部结构

缓存查找
objc-cache.mm
bucket_t * cache_t::find(cache_key_t k, id receiver)

bucket_t * cache_t::find(cache_key_t k, id receiver)
{
    assert(k != 0);

    bucket_t *b = buckets();
    mask_t m = mask();
    //k 是selector m是mask
    mask_t begin = cache_hash(k, m);
    //i 索引
    mask_t i = begin;
    do {
        if (b[i].key() == 0  ||  b[i].key() == k) { //找到就直接返回地址
            return &b[I];
        }
    } while ((i = cache_next(i, m)) != begin);//找不到就遍历前面一个

    // hack
    Class cls = (Class)((uintptr_t)this - offsetof(objc_class, cache));
    cache_t::bad_cache(receiver, (SEL)k, cls);
}

//内存不够就会重新设置mask 并清除缓存
void cache_t::expand()
{
    cacheUpdateLock.assertLocked();
    
    uint32_t oldCapacity = capacity();
    //存储空间变为原来的两倍
    uint32_t newCapacity = oldCapacity ? oldCapacity*2 : INIT_CACHE_SIZE;

    if ((uint32_t)(mask_t)newCapacity != newCapacity) {
        // mask overflow - can't grow further
        // fixme this wastes one bit of mask
        newCapacity = oldCapacity;
    }

    reallocate(oldCapacity, newCapacity);
}

方法缓存

散列表
类的cache里 ，cache里有个散列表数组 ，selector作为key & mask 获取到索引

算列表

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        MJGoodStudent *goodStudent = [[MJGoodStudent alloc] init];
        mj_objc_class *goodStudentClass = (__bridge mj_objc_class *)[MJGoodStudent class];
        
        [goodStudent goodStudentTest];
        [goodStudent studentTest];
        [goodStudent personTest];
        [goodStudent goodStudentTest];
        [goodStudent studentTest];
        
        cache_t cache = goodStudentClass->cache;
//        NSLog(@"%s %p", @selector(personTest), cache.imp(@selector(personTest)));
//        NSLog(@"%s %p", @selector(studentTest), cache.imp(@selector(studentTest)));
//        NSLog(@"%s %p", @selector(goodStudentTest), cache.imp(@selector(goodStudentTest)));
        //获取buckets散列表
        bucket_t *buckets = cache._buckets;
        //获取bucket
        bucket_t bucket = buckets[(long long)@selector(studentTest) & cache._mask];
        NSLog(@"%s %p", bucket._key, bucket._imp);
        
        for (int i = 0; i <= cache._mask; i++) {
            bucket_t bucket = buckets[I];
            if(bucket._key == 0) continue;
            NSLog(@"%lu %p", bucket._key, bucket._imp);
        }
        
    }
    return 0;
}

打印缓存里的方法

objc_msgSend

• OC中的方法调用，其实都是转换为objc_msgSend函数的调用
• objc_msgSend的执行流程可以分为3大阶段

  • 消息发送 (利用objc_msgSend尝试找到方法进行调用)

    
    消息发送阶段

  • 动态方法解析(找不到方法,进入到动态方法解析阶段 )

@implementation TGPerson
//Method类型的底层实现
struct method_t {
    SEL sel;
    char *types;
    IMP imp;
};

void c_other(id self, SEL _cmd)
{
    NSLog(@"c_other - %@ - %@", self, NSStringFromSelector(_cmd));
}

- (void)other
{
    NSLog(@"%s", __func__);
}

+ (BOOL)resolveInstanceMethod:(SEL)sel
{
    if (sel == @selector(test)) {
//第一种方式
        // 获取其他方法
        struct method_t *method = (struct method_t *)class_getInstanceMethod(self, @selector(other));
        // 动态添加test方法的实现
        class_addMethod(self, sel, method->imp, method->types);
//第二种方式
/**
  Method method = class_getInstanceMethod(self, @selector(other));
        class_addMethod(self, sel,
                        method_getImplementation(method),
                        method_getTypeEncoding(method));
*/
//第三种方式
// class_addMethod(self, sel, (IMP)c_other, "v16@0:8");

        // 返回YES代表有动态添加方法
        return YES;
    }
    return [super resolveInstanceMethod:sel];
}

@end

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        TGPerson *person = [[TGPerson alloc] init];
        [person test];
//        [TGPerson test];
    }
    return 0;
}

动态方法解析
@dynamic是告诉编译器不用自动生成getter和setter的实现，由用户自己实现
@synthesize表示如果属性没有手动实现setter和getter方法，编译器会自动加上这两个方法

• 消息转发(方法解析阶段 没有做任何操作，进入到消息转发阶段)

  
  消息转发

int main(int argc, const char * argv[]) {
   @autoreleasepool {
       TGPerson *person = [[TGPerson alloc] init];
       [person test:15];
   }
   return 0;
}
@implementation TGPerson
// 方法签名：返回值类型、参数类型
- (NSMethodSignature *)methodSignatureForSelector:(SEL)aSelector
{
   if (aSelector == @selector(test)) {
      // return [NSMethodSignature signatureWithObjCTypes:"v16@0:8"];
  return [NSMethodSignature signatureWithObjCTypes:"i@:I"];
   }
   return [super methodSignatureForSelector:aSelector];
}

// NSInvocation封装了一个方法调用，包括：方法调用者、方法名、方法参数
//    anInvocation.target 方法调用者
//    anInvocation.selector 方法名
//    [anInvocation getArgument:NULL atIndex:0]
- (void)forwardInvocation:(NSInvocation *)anInvocation
{
/**
  参数顺序：receiver、selector、other arguments
int age;
 [anInvocation getArgument:&age atIndex:2];
 NSLog(@"%d", age + 10);
*/

// anInvocation.target == [[MJCat alloc] init]
// anInvocation.selector == test:
// anInvocation的参数：15
// [[[TGCat alloc] init] test:15]
   [anInvocation invokeWithTarget:[[TGCat alloc] init]];
}

@end

源码阅读

• objc-msg-arm64.s

  • ENTRY _objc_msgSend
  • b.le LNilOrTagged
  • CacheLookup NORMAL
  • .macro CacheLookup
  • .macro CheckMiss
  • STATIC_ENTRY __objc_msgSend_uncached
  • .macro MethodTableLookup
  • __class_lookupMethodAndLoadCache3

• objc-runtime-new.mm

  • _class_lookupMethodAndLoadCache3
  • lookUpImpOrForward
  • getMethodNoSuper_nolock、search_method_list、log_and_fill_cache
  • cache_getImp、log_and_fill_cache、 getMethodNoSuper_nolock、log_and_fill_cache
  • _class_resolveInstanceMethod
  • _objc_msgForward_impcache

• objc-msg-arm64.s

  • STATIC_ENTRY __objc_msgForward_impcache
  • ENTRY __objc_msgForward

• Core Foundation

  • forwarding（不开源）

super 面试题

@implementation MJStudent

/*
 including the instance of the class that is to receive the message and the superclass at which to start searching for the method implementation
 [super message]的底层实现
 1.消息接收者仍然是子类对象
 2.从父类开始查找方法的实现
 */

//super调用，底层会转换为objc_msgSendSuper2函数的调用，接收2个参数
struct objc_super2 { //底层实现
   id receiver; // 消息接收者
  Class current_class; // 当前类类
};


struct objc_super { //重写c++实现
    __unsafe_unretained _Nonnull id receiver; // 消息接收者
    __unsafe_unretained _Nonnull Class super_class; // 消息接收者的父类
};

- (void)run
{
    // super调用的receiver仍然是MJStudent对象
    [super run];
    
//    struct objc_super arg = {self, [MJPerson class]};
//    objc_msgSendSuper(arg, @selector(run));
}

- (instancetype)init
{
    if (self = [super init]) {
        NSLog(@"[self class] = %@", [self class]); // MJStudent
        NSLog(@"[self superclass] = %@", [self superclass]); // MJPerson

        NSLog(@"--------------------------------");

        // objc_msgSendSuper({self, [MJPerson class]}, @selector(class));
        NSLog(@"[super class] = %@", [super class]); // MJStudent
        NSLog(@"[super superclass] = %@", [super superclass]); // MJPerson
    }
    return self;
}

@end

//@implementation NSObject
//
//- (Class)class
//{
//    return object_getClass(self);
//}
//
//- (Class)superclass
//{
//    return class_getSuperclass(object_getClass(self));
//}
//
//@end

isMemberOfClass、isKindOfClass

• isMemberOfClass底层实现

//判断类型是否相等
+ (BOOL)isMemberOfClass:(Class)cls {
    return object_getClass((id)self) == cls;
}
- (BOOL)isMemberOfClass:(Class)cls {
    return [self class] == cls;
}

• isKindOfClass 底层实现

//左边类型是否等于右边类型或是右边类型的子类
- (BOOL)isKindOfClass:(Class)cls {
    for (Class tcls = [self class]; tcls; tcls = tcls->superclass) {
        if (tcls == cls) return YES;
    }
    return NO;
}
+ (BOOL)isKindOfClass:(Class)cls {
    for (Class tcls = object_getClass((id)self); tcls; tcls = tcls->superclass) {
        if (tcls == cls) return YES;
    }
    return NO;
}

int main(int argc, const char * argv[]) {
    @autoreleasepool {
//        NSLog(@"%d", [[NSObject class] isKindOfClass:[NSObject class]]);
//        NSLog(@"%d", [[NSObject class] isMemberOfClass:[NSObject class]]);
//        NSLog(@"%d", [[MJPerson class] isKindOfClass:[MJPerson class]]);
//        NSLog(@"%d", [[MJPerson class] isMemberOfClass:[MJPerson class]]);
        
        // 这句代码的方法调用者不管是哪个类（只要是NSObject体系下的），都返回YES
      //object_getClass
        NSLog(@"%d", [NSObject isKindOfClass:[NSObject class]]); // 1
        NSLog(@"%d", [NSObject isMemberOfClass:[NSObject class]]); // 0
        NSLog(@"%d", [MJPerson isKindOfClass:[MJPerson class]]); // 0
        NSLog(@"%d", [MJPerson isMemberOfClass:[MJPerson class]]); // 0
        
//        id person = [[MJPerson alloc] init];
        
//        NSLog(@"%d", [person isMemberOfClass:[MJPerson class]]);
//        NSLog(@"%d", [person isMemberOfClass:[NSObject class]]);
        
//        NSLog(@"%d", [person isKindOfClass:[MJPerson class]]);
//        NSLog(@"%d", [person isKindOfClass:[NSObject class]]);
        
        
//        NSLog(@"%d", [MJPerson isMemberOfClass:object_getClass([MJPerson class])]);
//        NSLog(@"%d", [MJPerson isKindOfClass:object_getClass([NSObject class])]);
        
//        NSLog(@"%d", [MJPerson isKindOfClass:[NSObject class]]);
    }
    return 0;
}

  // 局部变量分配在栈空间
// 栈空间分配，从高地址到低地址
void test()
{
    long long a = 4; // 0x7ffee638bff8
    long long b = 5; // 0x7ffee638bff0
    long long c = 6; // 0x7ffee638bfe8
    long long d = 7; // 0x7ffee638bfe0
    
    NSLog(@"%p %p %p %p", &a, &b, &c, &d);
}

int main(int argc, char * argv[]) {
    @autoreleasepool {
//        test();
        return UIApplicationMain(argc, argv, nil, NSStringFromClass([AppDelegate class]));
    }
}

@implementation ViewController

/*
 1.print为什么能够调用成功？
 2.为什么self.name变成了ViewController等其他内容
 */
- (void)viewDidLoad {
    [super viewDidLoad];
//    struct abc = {  //隐藏的结构体
//        self,
//        [ViewController class]
//    };
//    objc_msgSendSuper2(abc, sel_registerName("viewDidLoad"));
    
//    NSObject *obj2 = [[NSObject alloc] init];
//
//    NSString *test = @"123";
    id cls = [MJPerson class];
    void *obj = &cls;

    [(__bridge id)obj print];
    
//    long long *p = (long long *)obj;
//    NSLog(@"%p %p", *(p+2), [ViewController class]);
    
//    struct MJPerson_IMPL
//    {
//        Class isa;
//        NSString *_name;
//    };
}
@end

画图分析 画图分析 画图分析

runtime的应用

• 类

//动态创建一个类（参数：父类，类名，额外的内存空间）
Class objc_allocateClassPair(Class superclass, const char *name, size_t extraBytes)

//注册一个类（要在类注册之前添加成员变量）
void objc_registerClassPair(Class cls) 
//销毁一个类
void objc_disposeClassPair(Class cls)

//获取isa指向的Class
Class object_getClass(id obj)
 MJPerson *person = [[MJPerson alloc] init];
object_getClass(person) //获取类对象
object_getClass([MJPerson class]) //获取元类对象

//设置isa指向的Class
Class object_setClass(id obj, Class cls)
 object_setClass(person, [MJCar class]);
  [person run]; //调用 MJCar的run方法

//判断一个OC对象是否为Class
BOOL object_isClass(id obj)
 NSLog(@"%d %d %d",
          object_isClass(person),
          object_isClass([MJPerson class]),
          object_isClass(object_getClass([MJPerson class]))
          );

//判断一个Class是否为元类
BOOL class_isMetaClass(Class cls)

//获取父类
Class class_getSuperclass(Class cls)


void testClass()
{
    // 创建类
    Class newClass = objc_allocateClassPair([NSObject class], "MJDog", 0);
    class_addIvar(newClass, "_age", 4, 1, @encode(int));
    class_addIvar(newClass, "_weight", 4, 1, @encode(int));
    class_addMethod(newClass, @selector(run), (IMP)run, "v@:");
    // 注册类
    objc_registerClassPair(newClass);
    
    MJPerson *person = [[MJPerson alloc] init];
    object_setClass(person, newClass);
    [person run];

    id dog = [[newClass alloc] init];
    [dog setValue:@10 forKey:@"_age"];
    [dog setValue:@20 forKey:@"_weight"];
    [dog run];

    NSLog(@"%@ %@", [dog valueForKey:@"_age"], [dog valueForKey:@"_weight"]);
    
    // 在不需要这个类时释放
    objc_disposeClassPair(newClass);
}

• 成员变量

获取一个实例变量信息
Ivar class_getInstanceVariable(Class cls, const char *name)

拷贝实例变量列表（最后需要调用free释放）
Ivar *class_copyIvarList(Class cls, unsigned int *outCount)

设置和获取成员变量的值
void object_setIvar(id obj, Ivar ivar, id value)
id object_getIvar(id obj, Ivar ivar)

动态添加成员变量（已经注册的类是不能动态添加成员变量的）
BOOL class_addIvar(Class cls, const char * name, size_t size, uint8_t alignment, const char * types)

获取成员变量的相关信息
const char *ivar_getName(Ivar v)
const char *ivar_getTypeEncoding(Ivar v)

void testIvars()
{
    // 获取成员变量信息
    //        Ivar ageIvar = class_getInstanceVariable([MJPerson class], "_age");
    //        NSLog(@"%s %s", ivar_getName(ageIvar), ivar_getTypeEncoding(ageIvar));
    
    // 设置和获取成员变量的值
    //        Ivar nameIvar = class_getInstanceVariable([MJPerson class], "_name");
    //
    //        MJPerson *person = [[MJPerson alloc] init];
    //        object_setIvar(person, nameIvar, @"123");
    //        object_setIvar(person, ageIvar, (__bridge id)(void *)10);
    //        NSLog(@"%@ %d", person.name, person.age);
    
    // 成员变量的数量
    unsigned int count;
    Ivar *ivars = class_copyIvarList([MJPerson class], &count);
    for (int i = 0; i < count; i++) {
        // 取出i位置的成员变量
        Ivar ivar = ivars[I];
        NSLog(@"%s %s", ivar_getName(ivar), ivar_getTypeEncoding(ivar));
    }
    free(ivars);
}

    Ivar *ivars = class_copyIvarList([UITextField class], &count);
    for (int i = 0; i < count; i++) {
        // 取出i位置的成员变量
        Ivar ivar = ivars[i];
        NSLog(@"%s %s", ivar_getName(ivar), ivar_getTypeEncoding(ivar));
    }
    free(ivars);

• 属性

获取一个属性
objc_property_t class_getProperty(Class cls, const char *name)

拷贝属性列表（最后需要调用free释放）
objc_property_t *class_copyPropertyList(Class cls, unsigned int *outCount)

动态添加属性
BOOL class_addProperty(Class cls, const char *name, const objc_property_attribute_t *attributes,
                  unsigned int attributeCount)

动态替换属性
void class_replaceProperty(Class cls, const char *name, const objc_property_attribute_t *attributes,
                      unsigned int attributeCount)

获取属性的一些信息
const char *property_getName(objc_property_t property)
const char *property_getAttributes(objc_property_t property)

• 方法

获得一个实例方法、类方法
Method class_getInstanceMethod(Class cls, SEL name)
Method class_getClassMethod(Class cls, SEL name)

方法实现相关操作
IMP class_getMethodImplementation(Class cls, SEL name) 
IMP method_setImplementation(Method m, IMP imp)
void method_exchangeImplementations(Method m1, Method m2) 

拷贝方法列表（最后需要调用free释放）
Method *class_copyMethodList(Class cls, unsigned int *outCount)

动态添加方法
BOOL class_addMethod(Class cls, SEL name, IMP imp, const char *types)

动态替换方法
IMP class_replaceMethod(Class cls, SEL name, IMP imp, const char *types)

获取方法的相关信息（带有copy的需要调用free去释放）
SEL method_getName(Method m)
IMP method_getImplementation(Method m)
const char *method_getTypeEncoding(Method m)
unsigned int method_getNumberOfArguments(Method m)
char *method_copyReturnType(Method m)
char *method_copyArgumentType(Method m, unsigned int index)


void myrun()
{
    NSLog(@"---myrun");
}

void test()
{
    MJPerson *person = [[MJPerson alloc] init];
    
    //        class_replaceMethod([MJPerson class], @selector(run), (IMP)myrun, "v");
    class_replaceMethod([MJPerson class], @selector(run), imp_implementationWithBlock(^{
        NSLog(@"123123");
    }), "v");
    
    [person run];
}

@implementation UIControl (Extension)

+ (void)load
{
    // hook：钩子函数
    Method method1 = class_getInstanceMethod(self, @selector(sendAction:to:forEvent:));
    Method method2 = class_getInstanceMethod(self, @selector(mj_sendAction:to:forEvent:));
    method_exchangeImplementations(method1, method2);
}

- (void)mj_sendAction:(SEL)action to:(id)target forEvent:(UIEvent *)event
{
    NSLog(@"%@-%@-%@", self, target, NSStringFromSelector(action));
    
    // 调用系统原来的实现
    [self mj_sendAction:action to:target forEvent:event];
    
//    [target performSelector:action];
    
//    if ([self isKindOfClass:[UIButton class]]) {
//        // 拦截了所有按钮的事件
//
//    }
}

@end


@implementation NSMutableArray (Extension)

+ (void)load
{
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        // 类簇：NSString、NSArray、NSDictionary，真实类型是其他类型
        Class cls = NSClassFromString(@"__NSArrayM");
        Method method1 = class_getInstanceMethod(cls, @selector(insertObject:atIndex:));
        Method method2 = class_getInstanceMethod(cls, @selector(mj_insertObject:atIndex:));
        method_exchangeImplementations(method1, method2);
    });
}

- (void)mj_insertObject:(id)anObject atIndex:(NSUInteger)index
{
    if (anObject == nil) return;
    
    [self mj_insertObject:anObject atIndex:index];
}

@end

@implementation NSMutableDictionary (Extension)

+ (void)load
{
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        Class cls = NSClassFromString(@"__NSDictionaryM");
        Method method1 = class_getInstanceMethod(cls, @selector(setObject:forKeyedSubscript:));
        Method method2 = class_getInstanceMethod(cls, @selector(mj_setObject:forKeyedSubscript:));
        method_exchangeImplementations(method1, method2);
        
        Class cls2 = NSClassFromString(@"__NSDictionaryI");
        Method method3 = class_getInstanceMethod(cls2, @selector(objectForKeyedSubscript:));
        Method method4 = class_getInstanceMethod(cls2, @selector(mj_objectForKeyedSubscript:));
        method_exchangeImplementations(method3, method4);
    });
}

- (void)mj_setObject:(id)obj forKeyedSubscript:(id<NSCopying>)key
{
    if (!key) return;
    
    [self mj_setObject:obj forKeyedSubscript:key];
}

- (id)mj_objectForKeyedSubscript:(id)key
{
    if (!key) return nil;
    
    return [self mj_objectForKeyedSubscript:key];
}

@end

• 字典转模型

@implementation NSObject (Json)

+ (instancetype)mj_objectWithJson:(NSDictionary *)json
{
    id obj = [[self alloc] init];
    
    unsigned int count;
    Ivar *ivars = class_copyIvarList(self, &count);
    for (int i = 0; i < count; i++) {
        // 取出i位置的成员变量
        Ivar ivar = ivars[i];
        NSMutableString *name = [NSMutableString stringWithUTF8String:ivar_getName(ivar)];
        [name deleteCharactersInRange:NSMakeRange(0, 1)];
        // 设值
        id value = json[name];
        [obj setValue:value forKey:name];
    }
    free(ivars);
    
    return obj;
}



int main(int argc, const char * argv[]) {
    @autoreleasepool {
        // 字典转模型
        NSDictionary *json = @{
                               @"id" : @20,
                               @"age" : @20,
                               @"weight" : @60,
                               @"name" : @"Jack"
                               };
        
        MJPerson *person = [MJPerson mj_objectWithJson:json];
        NSLog(@"123");
    }
    return 0;
}