iOS Runtime详解（新手也看得懂）

OBJC_EXPORT id objc_msgSend(id self, SEL op, ...)

//对象
struct objc_object {
 Class isa OBJC_ISA_AVAILABILITY;
};
//类
struct objc_class {
 Class isa OBJC_ISA_AVAILABILITY;
#if !__OBJC2__
 Class super_class     OBJC2_UNAVAILABLE;
 const char *name      OBJC2_UNAVAILABLE;
 long version      OBJC2_UNAVAILABLE;
 long info      OBJC2_UNAVAILABLE;
 long instance_size     OBJC2_UNAVAILABLE;
 struct objc_ivar_list *ivars    OBJC2_UNAVAILABLE;
 struct objc_method_list **methodLists   OBJC2_UNAVAILABLE;
 struct objc_cache *cache     OBJC2_UNAVAILABLE;
 struct objc_protocol_list *protocols   OBJC2_UNAVAILABLE;
#endif
} OBJC2_UNAVAILABLE;
//方法列表
struct objc_method_list {
 struct objc_method_list *obsolete   OBJC2_UNAVAILABLE;
 int method_count      OBJC2_UNAVAILABLE;
#ifdef __LP64__
 int space      OBJC2_UNAVAILABLE;
#endif
 /* variable length structure */
 struct objc_method method_list[1]   OBJC2_UNAVAILABLE;
}        OBJC2_UNAVAILABLE;
//方法
struct objc_method {
 SEL method_name      OBJC2_UNAVAILABLE;
 char *method_types     OBJC2_UNAVAILABLE;
 IMP method_imp      OBJC2_UNAVAILABLE;
}

typedef struct objc_class *Class;

struct objc_class {
 Class _Nonnull isa OBJC_ISA_AVAILABILITY;

#if !__OBJC2__
 Class _Nullable super_class    OBJC2_UNAVAILABLE;
 const char * _Nonnull name    OBJC2_UNAVAILABLE;
 long version      OBJC2_UNAVAILABLE;
 long info      OBJC2_UNAVAILABLE;
 long instance_size     OBJC2_UNAVAILABLE;
 struct objc_ivar_list * _Nullable ivars   OBJC2_UNAVAILABLE;
 struct objc_method_list * _Nullable * _Nullable methodLists   OBJC2_UNAVAILABLE;
 struct objc_cache * _Nonnull cache   OBJC2_UNAVAILABLE;
 struct objc_protocol_list * _Nullable protocols  OBJC2_UNAVAILABLE;
#endif

} OBJC2_UNAVAILABLE;

/// Represents an instance of a class.
struct objc_object {
 Class isa OBJC_ISA_AVAILABILITY;
};

/// A pointer to an instance of a class.
typedef struct objc_object *id;

runtime.h
/// An opaque type that represents a method in a class definition.代表类定义中一个方法的不透明类型
typedef struct objc_method *Method;
struct objc_method {
 SEL method_name           OBJC2_UNAVAILABLE;
 char *method_types          OBJC2_UNAVAILABLE;
 IMP method_imp           OBJC2_UNAVAILABLE;

- (void)logName
{
 NSLog(@"name");
}

Objc.h
/// An opaque type that represents a method selector.代表一个方法的不透明类型
typedef struct objc_selector *SEL;

@property SEL selector;

- (void)caculate(NSInteger)num;
- (void)caculate(CGFloat)num;

- (void)caculateWithInt(NSInteger)num;
- (void)caculateWithFloat(CGFloat)num;

/// A pointer to the function of a method implementation. 指向一个方法实现的指针
typedef id (*IMP)(id, SEL, ...); 
#endif

struct category_t { 
 const char *name; 
 classref_t cls; 
 struct method_list_t *instanceMethods; 
 struct method_list_t *classMethods;
 struct protocol_list_t *protocols;
 struct property_list_t *instanceProperties;
};

- (void)viewDidLoad {
 [super viewDidLoad];
 // Do any additional setup after loading the view, typically from a nib.
 //执行foo函数
 [self performSelector:@selector(foo:)];
}

+ (BOOL)resolveInstanceMethod:(SEL)sel {
 if (sel == @selector(foo:)) {//如果是执行foo函数，就动态解析，指定新的IMP
  class_addMethod([self class], sel, (IMP)fooMethod, "v@:");
  return YES;
 }
 return [super resolveInstanceMethod:sel];
}

void fooMethod(id obj, SEL _cmd) {
 NSLog(@"Doing foo");//新的foo函数
}

#import "ViewController.h"
#import "objc/runtime.h"

@interface Person: NSObject

@end

@implementation Person

- (void)foo {
 NSLog(@"Doing foo");//Person的foo函数
}

@end

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
 [super viewDidLoad];
 // Do any additional setup after loading the view, typically from a nib.
 //执行foo函数
 [self performSelector:@selector(foo)];
}

+ (BOOL)resolveInstanceMethod:(SEL)sel {
 return YES;//返回YES，进入下一步转发
}

- (id)forwardingTargetForSelector:(SEL)aSelector {
 if (aSelector == @selector(foo)) {
  return [Person new];//返回Person对象，让Person对象接收这个消息
 }
 
 return [super forwardingTargetForSelector:aSelector];
}

@end

#import "ViewController.h"
#import "objc/runtime.h"

@interface Person: NSObject

@end

@implementation Person

- (void)foo {
 NSLog(@"Doing foo");//Person的foo函数
}

@end

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
 [super viewDidLoad];
 // Do any additional setup after loading the view, typically from a nib.
 //执行foo函数
 [self performSelector:@selector(foo)];
}

+ (BOOL)resolveInstanceMethod:(SEL)sel {
 return YES;//返回YES，进入下一步转发
}

- (id)forwardingTargetForSelector:(SEL)aSelector {
 return nil;//返回nil，进入下一步转发
}

- (NSMethodSignature *)methodSignatureForSelector:(SEL)aSelector {
 if ([NSStringFromSelector(aSelector) isEqualToString:@"foo"]) {
  return [NSMethodSignature signatureWithObjCTypes:"v@:"];//签名，进入forwardInvocation
 }
 
 return [super methodSignatureForSelector:aSelector];
}

- (void)forwardInvocation:(NSInvocation *)anInvocation {
 SEL sel = anInvocation.selector;

 Person *p = [Person new];
 if([p respondsToSelector:sel]) {
  [anInvocation invokeWithTarget:p];
 }
 else {
  [self doesNotRecognizeSelector:sel];
 }

}

@end

//关联对象
void objc_setAssociatedObject(id object, const void *key, id value, objc_AssociationPolicy policy)
//获取关联的对象
id objc_getAssociatedObject(id object, const void *key)
//移除关联的对象
void objc_removeAssociatedObjects(id object)

typedef OBJC_ENUM(uintptr_t, objc_AssociationPolicy) {
 OBJC_ASSOCIATION_ASSIGN = 0,   /**< Specifies a weak reference to the associated object. */
 OBJC_ASSOCIATION_RETAIN_NONATOMIC = 1, /**< Specifies a strong reference to the associated object. 
           * The association is not made atomically. */
 OBJC_ASSOCIATION_COPY_NONATOMIC = 3, /**< Specifies that the associated object is copied. 
           * The association is not made atomically. */
 OBJC_ASSOCIATION_RETAIN = 01401,  /**< Specifies a strong reference to the associated object.
           * The association is made atomically. */
 OBJC_ASSOCIATION_COPY = 01403   /**< Specifies that the associated object is copied.
           * The association is made atomically. */
};

#import "ViewController.h"
#import "objc/runtime.h"

@interface UIView (DefaultColor)

@property (nonatomic, strong) UIColor *defaultColor;

@end

@implementation UIView (DefaultColor)

@dynamic defaultColor;

static char kDefaultColorKey;

- (void)setDefaultColor:(UIColor *)defaultColor {
 objc_setAssociatedObject(self, &kDefaultColorKey, defaultColor, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}

- (id)defaultColor {
 return objc_getAssociatedObject(self, &kDefaultColorKey);
}

@end

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
 [super viewDidLoad];
 // Do any additional setup after loading the view, typically from a nib.
 
 UIView *test = [UIView new];
 test.defaultColor = [UIColor blackColor];
 NSLog(@"%@", test.defaultColor);
}

@end

//class_addMethod(Class _Nullable __unsafe_unretained cls, SEL _Nonnull name, IMP _Nonnull imp, const char * _Nullable types)
class_addMethod([self class], sel, (IMP)fooMethod, "v@:");

@implementation ViewController

+ (void)load {
  static dispatch_once_t onceToken;
  dispatch_once(&onceToken, ^{
    Class class = [self class];
    SEL originalSelector = @selector(viewDidLoad);
    SEL swizzledSelector = @selector(jkviewDidLoad);
    
    Method originalMethod = class_getInstanceMethod(class,originalSelector);
    Method swizzledMethod = class_getInstanceMethod(class,swizzledSelector);
    
    //judge the method named swizzledMethod is already existed.
    BOOL didAddMethod = class_addMethod(class, originalSelector, method_getImplementation(swizzledMethod), method_getTypeEncoding(swizzledMethod));
    // if swizzledMethod is already existed.
    if (didAddMethod) {
      class_replaceMethod(class, swizzledSelector, method_getImplementation(originalMethod), method_getTypeEncoding(originalMethod));
    }
    else {
      method_exchangeImplementations(originalMethod, swizzledMethod);
    }
  });
}

- (void)jkviewDidLoad {
  NSLog(@"替换的方法");
  
  [self jkviewDidLoad];
}

- (void)viewDidLoad {
  NSLog(@"自带的方法");
  
  [super viewDidLoad];
}

@end

NSLog(@"self->isa:%@",self->isa); 
NSLog(@"self class:%@",[self class]); 

- (void)setName:(NSString *)newName { 
   [self willChangeValueForKey:@"name"];  //KVO 在调用存取方法之前总调用 
   [super setValue:newName forKey:@"name"]; //调用父类的存取方法 
   [self didChangeValueForKey:@"name"];   //KVO 在调用存取方法之后总调用
}

- (id)initWithCoder:(NSCoder *)aDecoder {
  if (self = [super init]) {
    unsigned int outCount;
    Ivar * ivars = class_copyIvarList([self class], &outCount);
    for (int i = 0; i < outCount; i ++) {
      Ivar ivar = ivars[i];
      NSString * key = [NSString stringWithUTF8String:ivar_getName(ivar)];
      [self setValue:[aDecoder decodeObjectForKey:key] forKey:key];
    }
  }
  return self;
}

- (void)encodeWithCoder:(NSCoder *)aCoder {
  unsigned int outCount;
  Ivar * ivars = class_copyIvarList([self class], &outCount);
  for (int i = 0; i < outCount; i ++) {
    Ivar ivar = ivars[i];
    NSString * key = [NSString stringWithUTF8String:ivar_getName(ivar)];
    [aCoder encodeObject:[self valueForKey:key] forKey:key];
  }
}

- (instancetype)initWithDict:(NSDictionary *)dict {

  if (self = [self init]) {
    //(1)获取类的属性及属性对应的类型
    NSMutableArray * keys = [NSMutableArray array];
    NSMutableArray * attributes = [NSMutableArray array];
    /*
     * 例子
     * name = value3 attribute = T@"NSString",C,N,V_value3
     * name = value4 attribute = T^i,N,V_value4
     */
    unsigned int outCount;
    objc_property_t * properties = class_copyPropertyList([self class], &outCount);
    for (int i = 0; i < outCount; i ++) {
      objc_property_t property = properties[i];
      //通过property_getName函数获得属性的名字
      NSString * propertyName = [NSString stringWithCString:property_getName(property) encoding:NSUTF8StringEncoding];
      [keys addObject:propertyName];
      //通过property_getAttributes函数可以获得属性的名字和@encode编码
      NSString * propertyAttribute = [NSString stringWithCString:property_getAttributes(property) encoding:NSUTF8StringEncoding];
      [attributes addObject:propertyAttribute];
    }
    //立即释放properties指向的内存
    free(properties);

    //(2)根据类型给属性赋值
    for (NSString * key in keys) {
      if ([dict valueForKey:key] == nil) continue;
      [self setValue:[dict valueForKey:key] forKey:key];
    }
  }
  return self;

}