方法交换与继承关系

条件：ViewController在load方法内交换了viewDidLoad方法，但子类的viewDidLoad没有写[super viewDidLoad]
问：子类的viewDidLoad执行的是父类交换后的还是自己的？
答：只执行自己的，不会去找父类的方法。方法查找过程，自身实现的，不会去查找父类的。

//父类
@implementation ParentVC

- (void)viewDidLoad {
    [super viewDidLoad];
    NSLog(@"======ParentVC======");
}

@end

// 方法交换
@implementation ParentVC (Catrgory)

+ (void)load {
    Method origin = class_getInstanceMethod([self class], @selector(viewDidLoad));
    Method swizz = class_getInstanceMethod([self class], @selector(llviewDidLoad));
    
    BOOL didAdd = class_addMethod([self class], @selector(viewDidLoad), method_getImplementation(swizz), method_getTypeEncoding(swizz));
    
    if (didAdd) {
        class_replaceMethod([self class], @selector(llviewDidLoad), method_getImplementation(origin), method_getTypeEncoding(origin));
    } else {
        method_exchangeImplementations(origin, swizz);
    }
}

- (void)llviewDidLoad {
    NSLog(@"======ParentVC+Catrgory======");
}

@end

//子类
- (void)viewDidLoad {
    NSLog(@"======Student======");
   }

执行结果如下：

2020-12-15 20:01:56.121563+0800 test[90699:14720833] ======ParentVC+Catrgory======
//以下是子类调用打印
2020-12-15 20:02:06.133559+0800 test[90699:14720833] ======Student======
2020-12-15 20:02:06.133993+0800 test[90699:14720833] ======Student======

若子类代码修改如下：

//子类
- (void)viewDidLoad {
   [super viewDidLoad];
    NSLog(@"======Student======");
   }

2020-12-15 20:07:40.416351+0800 test[90724:14725040] ======ParentVC+Catrgory======
//以下是子类调用打印
2020-12-15 20:07:46.244325+0800 test[90724:14725040] ======ParentVC+Catrgory======
2020-12-15 20:07:46.244549+0800 test[90724:14725040] ======Student======
2020-12-15 20:07:46.244963+0800 test[90724:14725040] ======ParentVC+Catrgory======
2020-12-15 20:07:46.245082+0800 test[90724:14725040] ======Student======