[Objective-C Runtime] 成员变量与属性

typedef struct objc_ivar *Ivar;

struct objc_ivar {
    char *ivar_name OBJC2_UNAVAILABLE; // 变量名。
    char *ivar_type OBJC2_UNAVAILABLE; // 变量类型。
    int ivar_offset OBJC2_UNAVAILABLE; // 基地址偏移量，在对成员变量寻址时使用。

#ifdef __LP64__
    int space OBJC2_UNAVAILABLE;
#endif} 

typedef struct objc_property *objc_property_t;

typedef struct {
    const char * _Nonnull name;           /**< The name of the attribute */
    const char * _Nonnull value;       
                   /**< The value of the atribute (usually empty) */
} objc_property_attribute_t;

NSString * runtimePropertyGetterIMP(id self, SEL _cmd){
    Ivar ivar = class_getInstanceVariable([self class], "_runtimeProperty");    
    return object_getIvar(self, ivar);
}

void runtimePropertySetterIMP(id self, SEL _cmd, NSString *value){
    Ivar ivar = class_getInstanceVariable([self class], "_runtimeProperty");    NSString *aValue = (NSString *)object_getIvar(self, ivar);    if (![aValue isEqualToString:value]) {
        object_setIvar(self, ivar, value);
    }
}

- (void)verifyPropertyAndIvar{    

#pragma clang diagnostic push#pragma clang diagnostic ignored "-Wundeclared-selector"
    
    //1、Add property and getter/setter method
    Class cls = objc_allocateClassPair([Animal class], "Panda", 0);    
    //add instance variable
    BOOL isSuccess = class_addIvar(cls, "_runtimeProperty", sizeof(cls), log2(sizeof(cls)), @encode(NSString));    NSLog(@"%@", isSuccess ? @"成功" : @"失败");//print 成功
    
    //add attributes
    objc_property_attribute_t type = {"T", "@\"NSString\""};
    objc_property_attribute_t ownership = {"C", ""};//C = Copy
    objc_property_attribute_t isAutomic = {"N", ""};// N = nonatomic
    objc_property_attribute_t backingVar = {"V", "_runtimeProperty"};
    objc_property_attribute_t attrubutes[] = {type, ownership, isAutomic, backingVar};
    class_addProperty(cls, "runtimeProperty", attrubutes, 4);
    class_addMethod(cls, @selector(runtimeProperty), (IMP)runtimePropertyGetterIMP, "@@:");
    class_addMethod(cls, @selector(setRuntimeProperty), (IMP)runtimePropertySetterIMP, "V@:");
    
    objc_registerClassPair(cls);    
    //2、print all properties
    unsigned int count = 0;
    objc_property_t *properties = class_copyPropertyList(cls, &count);    for (int32_t i = 0; i < count; i ++) {
        objc_property_t property = properties[i];    
    
        NSLog(@"%s, %s\n", property_getName(property), property_getAttributes(property)); 
       //print: _runtimeProperty, T@"NSString",C,N,V_runtimeProperty
    }
    free(properties); 
          
    //3、print all Ivar
    unsigned int outCount = 0;
    Ivar *ivars = class_copyIvarList(cls, &outCount);   
          
     for (int32_t i = 0; i < outCount; i ++) {
        Ivar ivar = ivars[i];       
        NSLog(@"%s, %s\n", ivar_getName(ivar), ivar_getTypeEncoding(ivar));        
      //print:_runtimeProperty, {NSString=#}
       
    }
    free(ivars); 
          
        
    //4、use property
    id panda = [[cls alloc] init];
    [panda performSelector:@selector(setRuntimeProperty) withObject:@"set-property"];    
          
    NSString *propertyValue = [panda performSelector:@selector(runtimeProperty)];   
    NSLog(@"return value = %@", propertyValue);    
    //print: return value = set-property
    
    //5、destory
    panda = nil;
    objc_disposeClassPair(cls);    
    #pragma clang diagnostic pop
    }

成功
runtimeProperty, T@"NSString",C,N,V_runtimeProperty
_runtimeProperty, {NSString=#}return value = set-property