Objective-C中的runtime

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

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

/// An opaque type that represents an Objective-C class.
typedef struct objc_class *Class;

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;
/* Use `Class` instead of `struct objc_class *` */

/// An opaque type that represents a method selector.
typedef struct objc_selector *SEL;

/// An opaque type that represents a method in a class definition.
typedef struct objc_method *Method;

struct objc_method {
    SEL method_name                                          OBJC2_UNAVAILABLE;
    char *method_types                                       OBJC2_UNAVAILABLE;
    IMP method_imp                                           OBJC2_UNAVAILABLE;
}                                                            OBJC2_UNAVAILABLE;

/// An opaque type that represents an instance variable.
typedef struct objc_ivar *Ivar;

struct objc_ivar {
    char *ivar_name                                          OBJC2_UNAVAILABLE;
    char *ivar_type                                          OBJC2_UNAVAILABLE;
    int ivar_offset                                          OBJC2_UNAVAILABLE;
#ifdef __LP64__
    int space                                                OBJC2_UNAVAILABLE;
#endif
} 

/// An opaque type that represents an Objective-C declared property.
typedef struct objc_property *objc_property_t;

/// A pointer to the function of a method implementation. 
#if !OBJC_OLD_DISPATCH_PROTOTYPES
typedef void (*IMP)(void /* id, SEL, ... */ ); 
#else
typedef id (*IMP)(id, SEL, ...); 
#endif

typedef struct objc_cache *Cache                             OBJC2_UNAVAILABLE;

struct objc_cache {
    unsigned int mask /* total = mask + 1 */                 OBJC2_UNAVAILABLE;
    unsigned int occupied                                    OBJC2_UNAVAILABLE;
    Method buckets[1]                                        OBJC2_UNAVAILABLE;
};

id returnValue = [someObject message:parm];

id objc_msgSend (id self, SEL _cmd, ...);

id returnValue objc_mgSend(someObject, @selector(message:), parm);

/**
 消息转发第一步：对象在收到无法解读的消息后，首先调用此方法，可用于动态添加方法，方法决定是否动态添加方法。如果返回YES，则调用class_addMethod动态添加方法，消息得到处理，结束；如果返回NO，则进入下一步；
 */
+ (BOOL)resolveInstanceMethod:(SEL)sel
{
    return NO;
}

/**
 当前接收者还有第二次机会处理未知的选择子，在这一步中，运行期系统会问：能不能把这条消息转给其他接收者来处理。会进入此方法，用于指定备选对象响应这个selector，不能指定为self。如果返回某个对象则会调用对象的方法，结束。如果返回nil，则进入下一步；
 */
- (id)forwardingTargetForSelector:(SEL)aSelector
{
    return nil;
}

/**
 这步我们要通过该方法签名，如果返回nil，则消息无法处理。如果返回methodSignature，则进入下一步。
 */
- (NSMethodSignature *)methodSignatureForSelector:(SEL)aSelector
{
    if ([NSStringFromSelector(aSelector) isEqualToString:@"study"])
    {
        return [NSMethodSignature signatureWithObjCTypes:"v@:"];
    }
    return [super methodSignatureForSelector:aSelector];
}

/**
 这步调用该方法，我们可以通过anInvocation对象做很多处理，比如修改实现方法，修改响应对象等，如果方法调用成功，则结束。如果失败，则进入doesNotRecognizeSelector方法。
 */
- (void)forwardInvocation:(NSInvocation *)anInvocation
{
    [anInvocation setSelector:@selector(play)];
    [anInvocation invokeWithTarget:self];
}

/**
 抛出异常，此异常表示选择子最终未能得到处理。
 */
- (void)doesNotRecognizeSelector:(SEL)aSelector
{
    NSLog(@"无法处理消息：%@", NSStringFromSelector(aSelector));
}

+ (void)load
{
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{

        SEL originalSelector = @selector(willMoveToSuperview:);
        SEL swizzledSelector = @selector(myWillMoveToSuperview:);

        Method originalMethod = class_getInstanceMethod(self, originalSelector);
        Method swizzledMethod = class_getInstanceMethod(self, swizzledSelector);

        BOOL didAddMethod = class_addMethod(self, 
                                            originalSelector,
                                            method_getImplementation(swizzledMethod),
                                            method_getTypeEncoding(swizzledMethod));

        if (didAddMethod) {
            class_replaceMethod(self, 
                                swizzledSelector, 
                                method_getImplementation(originalMethod),
                                method_getTypeEncoding(originalMethod));
        } else {
            method_exchangeImplementations(originalMethod, swizzledMethod);
        }
    });
}

- (void)myWillMoveToSuperview:(UIView *)newSuperview
{
    NSLog(@"WillMoveToSuperview: %@", self); 
    [self myWillMoveToSuperview:newSuperview];
}

#import "ViewController.h"
#import <objc/runtime.h>
#import "People.h"
#import "Chinese.h"

@interface ViewController ()

@end

@implementation ViewController


/* 类、父类、元类关系结构的示例代码 */
- (void)testClass
{
    Chinese *ch = [[Chinese alloc] init];
    NSLog(@"获取Chinese对象ch所属的类是：%@,其父类是：%@",object_getClass(ch),class_getSuperclass(object_getClass(ch)));
    Class cls = objc_getMetaClass("Chinese");

    NSLog(@"元类是：%@, 元类的父类：%@, 元类的isa:%@",cls,class_getSuperclass(cls),object_getClass(cls));

    People *peo = [[People alloc] init];
    NSLog(@"获取People对象peo所属的类是：%@,其父类是：%@",object_getClass(peo),class_getSuperclass(object_getClass(peo)));
    cls = objc_getMetaClass("People");
    NSLog(@"元类是：%@, 元类的父类：%@, 元类的isa:%@",cls,class_getSuperclass(cls),object_getClass(cls));

    
    
    cls = objc_getMetaClass("UIView");
    NSLog(@"元类是： %@,父类是：%@, cls的isa是： %@", cls, class_getSuperclass(cls), object_getClass(cls)); // Print: YES, UIView, UIResponder, NSObject

    
    cls = objc_getMetaClass("NSObject");
    NSLog(@"元类是： %@, 父类是：%@, cls的isa是：%@", cls, class_getSuperclass(cls), object_getClass(cls)); // Print: YES, NSObject, NSObject, NSObject
}

获取Chinese对象ch所属的类是：Chinese,其父类是：People
元类是：Chinese, 元类的父类：People, 元类的isa:NSObject
获取People对象peo所属的类是：People,其父类是：NSObject
元类是：People, 元类的父类：NSObject, 元类的isa:NSObject
元类是： UIView,父类是：UIResponder, cls的isa是： NSObject
元类是： NSObject, 父类是：NSObject, cls的isa是：NSObject

元类是：Chinese, 元类的父类：People, 元类的isa:NSObject

- (void)runtimeConstuct
{
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wundeclared-selector"
    
    
    // 创建并注册一个类，并往类中添加方法
    Class cls = objc_allocateClassPair(People.class, "Janpanese", 0);
    class_addMethod(cls, @selector(testRuntimeMethod), (IMP)testRuntimeMethodIMP, "i@:@");
    objc_registerClassPair(cls);
    
    
    // 2: Create instance of class, print some info about class and associated meta class.
    id sub = [[cls alloc] init];
    NSLog(@"类是：%@, 父类是：%@", object_getClass(sub), class_getSuperclass(object_getClass(sub))); // Print: Janpanese, People
    Class metaCls = objc_getMetaClass("Janpanese");
    NSLog(@"元类是：%@, 父类是：%@,metaCls的isa是：%@", metaCls, class_getSuperclass(metaCls), object_getClass(metaCls)); // Print: YES, Janpanese, SuperClass, NSObject

    
    
    // 3: Methods of class.
    unsigned int outCount = 0;
    Method *methods = class_copyMethodList(cls, &outCount);
    for (int32_t i = 0; i < outCount; i++) {
        Method method = methods[i];
        NSLog(@"方法名：%@, %s", NSStringFromSelector(method_getName(method)), method_getTypeEncoding(method));
    }
    // Print: testRuntimeMethod, i@:@
    free(methods);
    
    
    // 4: Call method.
    int32_t result = (int) [sub performSelector:@selector(testRuntimeMethod) withObject:@{@"a":@"para_a", @"b":@"para_b"}];
    NSLog(@"函数返回值：%d", result); // Print: 99
    
    
    // 5: Destory instances and class.
    // Destroy instances of cls class before destroy cls class.
    sub = nil;
    // Do not call this function if instances of the cls class or any subclass exist.
    objc_disposeClassPair(cls);
    
#pragma clang diagnostic pop
    
}

类是：Janpanese, 父类是：People
元类是：Janpanese, 父类是：People,metaCls的isa是：NSObject
方法名：testRuntimeMethod, i@:@
testRuntimeMethodIMP : {
    a = "para_a";
    b = "para_b";
}
函数返回值：99