method_exchangeImplementations运行时动态改变两个方法的实现 ~~~ /**  * Exchanges the implementations of two methods.  *  * @param m1 Method to exchange with second method.  * @param m2 Method to exchange with first method.  *  * @note This is an atomic version of the following:  *  \code  *  IMP imp1 = method_getImplementation(m1);  *  IMP imp2 = method_getImplementation(m2);  *  method_setImplementation(m1, imp2);  *  method_setImplementation(m2, imp1);  *  \endcode  */ OBJC_EXPORT void method_exchangeImplementations(Method m1, Method m2)      __OSX_AVAILABLE_STARTING(__MAC_10_5, __IPHONE_2_0); ~~~ 代码： ~~~ - (void)viewDidLoad { [super viewDidLoad]; // Do any additional setup after loading the view, typically from a nib. Method m1 = class_getInstanceMethod([self class], @selector(testExchange1)); Method m2 = class_getInstanceMethod([self class], @selector(testExchange2)); [self testExchange1]; [self testExchange2]; method_exchangeImplementations(m1, m2); [self testExchange1]; [self testExchange2]; } - (void) testExchange1 { NSLog(@"%s", __func__); } - (void) testExchange2 { NSLog(@"%s", __func__); } ~~~ 输出： ~~~ 2015-11-02 13:38:40.264 02-runtime[2485:68367] -[ViewController testExchange1] 2015-11-02 13:38:40.266 02-runtime[2485:68367] -[ViewController testExchange2] 2015-11-02 13:38:40.281 02-runtime[2485:68367] -[ViewController testExchange2] 2015-11-02 13:38:40.281 02-runtime[2485:68367] -[ViewController testExchange1] ~~~ 通过代码相信很容易理解吧