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OC是运行时语言，只有在程序运行时，才会去确定对象的类型，并调用类与对象相应的方法。利用runtime机制让我们可以在程序运行时动态修改类、对象中的所有属性、方法，就算是私有方法以及私有属性都是可以动态修改的。本文旨在对runtime的部分特性小试牛刀，更多更全的方法可以参考系统API文件，

新建两个类ClassOne和ClassTwo

#import <Foundation/Foundation.h>

@interface ClassOne : NSObject{
NSString *_publicVar1;
NSString *_publicVar2;
}

@property(nonatomic,copy) NSString *publicProperty1;
@property(nonatomic,copy) NSString *publicProperty2;

- (void) testClassOneWithArg1:(NSString *)arg1;
@end


#import "ClassOne.h"

@interface ClassOne()
@property(nonatomic,copy) NSString *privateProperty1;
@property(nonatomic,copy) NSString *privateProperty2;

@end

@implementation ClassOne{
    NSString *_privateVar1;
    NSString *_privateVar2;
}

- (void)testClassOneWithArg1:(NSString *)arg1{
NSLog(@"this is CalssOne, arg1:%@",arg1);
}

- (void)testClassOneWithArg1:(NSString *)arg1 arg2:arg2{
NSLog(@"this is CalssOne, arg1:%@ arg2:%@",arg1,arg2);
}
@end

#import <Foundation/Foundation.h>

@interface ClassTwo : NSObject
- (void) testClassTwoWithArg1:(NSString *)arg1 arg2:(NSString *)arg2;
@end


#import "ClassTwo.h"

@implementation ClassTwo
- (void)testClassTwoWithArg1:(NSString *)arg1 arg2:(NSString *)arg2{
NSLog(@"this is ClassTwo arg1:%@,arg2:%@",arg1,arg2);
}
@end

1.拷贝对象

ClassOne *one = [ClassOne new];
id onec1 = object_copy(one,sizeof(one));

2.给类添加方法

ClassOne *one = [ClassOne new];
class_addMethod([ClassOne class], @selector(testClassOneWithArg1:arg2:arg3:), (IMP)testClassOne , "i@:@@@");
[ one  testClassOneWithArg1:@"arg1" arg2:@"arg2" arg3:@"arg3"];

//方法对应的C函数
int testClassOne(id self,SEL _cmd, NSString *arg1,NSString *arg2,NSString *arg3){
NSLog(@"this is a test function  add to ClassOne as a methad with arg1:%@  arg2:%@ and arg3:%@",arg1,arg2,arg3);
return 10;
}

3.添加属性（方式一）

//属性类型
objc_property_attribute_t type = { "T", "@\"NSString\"" };
//访问类型
objc_property_attribute_t ownership = { "C", "" };
//对应成员变量名称
objc_property_attribute_t backingivar  = { "V", "_testPropertyName" };
objc_property_attribute_t attrs[] = { type, ownership, backingivar };
class_addProperty([ClassOne class], "testPropertyName", attrs, 3);
class_addMethod([ClassOne class], @selector(testPropertyName), (IMP)testPropertyNameGetter , "@:@@");
class_addMethod([ClassOne class], @selector(setTestPropertyName:), (IMP)testPropertyNameSetter, "v:@@@");


//属性对应的Getter方法
NSString* testPropertyNameGetter(id self,SEL _cmd){
Ivar ivar = class_getInstanceVariable([ClassOne class], "_testPropertyName");
return object_getIvar(self, ivar);
}

//属性对应的Setter方法
void testPropertyNameSetter(id self,SEL _cmd,NSString *testPropertyNameValue){
Ivar ivar = class_getInstanceVariable([ClassOne class], "_testPropertyName");
object_setIvar(self, ivar, testPropertyNameValue);
}

4.添加属性（方式2）

ClassOne *one = [ClassOne new];
objc_setAssociatedObject(one, "objTag", @"value", OBJC_ASSOCIATION_COPY);
NSString *value = objc_getAssociatedObject(one, "objTag");
NSLog(@"通过Associate设置:%@",value);

5.获取类的名称

ClassOne *one = [ClassOne new];
const char *className = object_getClassName(one);
NSLog(@"className:%@",[NSString stringWithUTF8String:className]);

6.获取一个类的所有方法

UInt count;
Method *methods = class_copyMethodList([ClassOne class], &count);
for (int i = 0; i < count; i++) {
Method method = methods[i];
SEL sel = method_getName(method);
NSLog(@"方法名:%@",NSStringFromSelector(sel));
}

7.获取一个类的所有属性

uint propertyCount;
objc_property_t *ps = class_copyPropertyList([ClassOne class], &propertyCount);
for (uint i = 0; i < propertyCount; i++) {
objc_property_t property = ps[i];
const char *propertyName = property_getName(property);
const char *propertyAttributes = property_getAttributes(property);
NSLog(@"propertyName:%@",[NSString stringWithUTF8String:propertyName]);
NSLog(@"propertyAttributes:%@",[NSString stringWithUTF8String:propertyAttributes]);
}

8.获取类的所有成员变量

uint ivarCount;
Ivar *ivars = class_copyIvarList([ClassOne class], &ivarCount);
for (uint i = 0; i < ivarCount; i++) {
Ivar ivar = ivars[i];
const char *ivarName = ivar_getName(ivar);
NSLog(@"ivarName:%@",[NSString stringWithUTF8String:ivarName]);
}

9.获得成员变量类型

uint ivarCount;
Ivar *ivars = class_copyIvarList([ClassOne class], &ivarCount);
for (uint i = 0; i < ivarCount; i++) {
Ivar ivar = ivars[i];
const char *ivarName = ivar_getName(ivar);
const char *type = ivar_getTypeEncoding(ivar);
NSLog(@"ivarName=%@,type=%@",[NSString stringWithUTF8String:ivarName],[NSString stringWithUTF8String:type]);
}

代码demo