class_addMethod、class_replaceMethod

1、class_addMethod 添加方法

@implementation ViewController

+ (void)load
{
   //获取实例方法中存在的方法
    Method method = class_getInstanceMethod([self class], @selector(sayHello));
    
  //添加一个方法personSayHello， 它的实现指向sayHello的实现
    BOOL res = class_addMethod([self class], @selector(personSayHello), method_getImplementation(method), method_getTypeEncoding(method));
}

- (void)viewDidLoad
{
    [super viewDidLoad];
    [self performSelector:@selector(personSayHello)];
}

- (void)sayHello
{
    NSLog(@"say hello");
}

log:

2018-09-30 15:25:07.935242+0800 method_test[55232:4354234] say goodbye

2 、class_replaceMethod 替换方法的实现

@implementation ViewController

+ (void)load
{
    Method method = class_getInstanceMethod([self class], @selector(sayGoodBye));
    //替换方法
    class_replaceMethod([self class], @selector(sayHello), method_getImplementation(method), method_getTypeEncoding(method));
}

- (void)viewDidLoad
{
    [super viewDidLoad];
    [self sayHello];
}

- (void)sayHello
{
    NSLog(@"say hello");
}

- (void)sayGoodBye
{
    NSLog(@"say goodbye");
}
@end

log

2018-09-30 15:25:08.116772+0800 method_test[55232:4354234] say goodbye

3、method_exchangeImplementations 交换方法实现

@implementation ViewController

+ (void)load
{
    Method sayGoodsByeMethod = class_getInstanceMethod([self class], @selector(sayGoodBye));
    Method sayHelloMethod = class_getInstanceMethod([self class], @selector(sayHello));
  //交换两个方法
    method_exchangeImplementations(sayHelloMethod, sayGoodsByeMethod);
}

- (void)viewDidLoad
{
    [super viewDidLoad];
    [self sayHello];
    [self sayGoodBye];
}

- (void)sayHello
{
    NSLog(@"say hello");
}

- (void)sayGoodBye
{
    NSLog(@"say goodbye");
}

log:

2018-09-30 15:30:39.848247+0800 method_test[55294:4362459] say goodbye
2018-09-30 15:30:39.848388+0800 method_test[55294:4362459] say hello