2. 动态交换两个方法的实现

Teacher: What's your name?

XiaoMing: My name is XiaoMing.

Teacher: Pardon?

XiaoMing: My name is __

在程序当中，假设XiaoMing的第一次回答为firstSay，后来被Runtime交换了一个名字叫secondSay的方法，最终再调用firstSay的时候，其实是调用了secondSay的实现。那么，Runtime是如何做到的呢？

2）Step：

①动态找到firstSay和secondSay方法

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

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

②交换两个方法

method_exchangeImplementations(m1, m2);

3）Show Code：

-(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);

}