RunTime简称运行时,就是系统在运行的时候的一些机制，其中最主要的是消息机制。

1. 对于C语言，函数的调用在编译的时候会决定调用哪个函数（ C语言的函数调用请看这里 ）。编译完成之后直接顺序执行，无任何二义性。

2. OC的函数调用成为消息发送。属于动态调用过程。在编译的时候并不能决定真正调用哪个函数（事实证明，在编 译阶段，OC可以调用任何函数，即使这个函数并未实现，只要申明过就不会报错。而C语言在编译阶段就会报错）。

3. 只有在真正运行的时候才会根据函数的名称找 到对应的函数来调用。

In the legacy runtime, if you change the layout of instance variables in a class, you must recompile classes that inherit from it.

1. In the modern runtime, if you change the layout of instance variables in a class, you do not have to recompile classes that inherit from it. In addition, the modern runtime supports instance variable synthesis for declared properties (see Declared Properties in The Objective-C Programming Language).

[self.loginBt login];

objc_msgSend(self.loginB,@selector(login));

既然是“如来神掌”，简直可以无法无天啦，当街拦下一个人问道“这是马还是鹿啊？”，那人看是Runtime大人惧怕道“Runtime大人，您说是马就是马，是鹿就是鹿~”。Runtime大快“wow哈哈哈~，见你乖巧，我也不为难于你。你缺头驴是吧？，本大人现在造一头送于你，迁回家便是！喔~哈哈哈”。

Ivar *ivar = class_copyIvarList([self.xiaoMing class], &count);

const char *varName = ivar_getName(var);

object_setIvar(self.xiaoMing, var, @"Minggo");

    	if ([name isEqualToString:@"_englishName"]) {
        	object_setIvar(self.xiaoMing, var, @"Minggo");
        	break;
    	}
	}
	NSLog(@"XiaoMing first answer is %@",self.xiaoMing.englishName);
	self.nameTf.text = self.xiaoMing.englishName;
}

Method m1 = class_getInstanceMethod([self.xiaoMing class], @selector(firstSay));
Method m2 = class_getInstanceMethod([self.xiaoMing class], @selector(secondSay));

method_exchangeImplementations(m1, m2);

-(void)answer{

	Method m1 = class_getInstanceMethod([self.xiaoMing class], @selector(firstSay));
	Method m2 = class_getInstanceMethod([self.xiaoMing class], @selector(secondSay));

	method_exchangeImplementations(m1, m2);
	NSString *secondName = [self.xiaoMing firstSay];

	self.nameTf.text = secondName;
	NSLog(@"XiaoMing:My name is %@",secondName);
}

class_addMethod([self.xiaoMing class], @selector(guess), (IMP)guessAnswer, "v@:");

[self.xiaoMing performSelector:@selector(guess)];

void guessAnswer(id self,SEL _cmd){
	NSLog(@"He is from GuangTong");
}

    	[self.xiaoMing performSelector:@selector(guess)];

	} else{
    	NSLog(@"Sorry,I don't know");
	}
	self.cityTf.text = @"GuangTong";
}

void guessAnswer(id self,SEL _cmd){

	NSLog(@"He is from GuangTong");

}

Teacher: What's your Chinese name?
XiaoMing: I have no one.
LiHua: You should have one.
LiHua: Your Chinese name is __

#import "XiaoMing.h"

@interface XiaoMing (MutipleName)

@property(nonatomic,copy) NSString *chineseName;

@end

#import "XiaoMing+MutipleName.h"
#import <objc/runtime.h>

@implementation XiaoMing (MutipleName)

char cName;

-(void)setChineseName:(NSString *) chineseName{
	objc_setAssociatedObject(self, &cName, chineseName, OBJC_ASSOCIATION_COPY_NONATOMIC);
}

-(NSString *)chineseName{
	return objc_getAssociatedObject(self, &cName);
}

@end

-(void)answer{
	NSLog(@"My Chinese name is %@",self.xiaoMing.chineseName);
	self.chineseNameTf.text = self.xiaoMing.chineseName;
}