建立一個UIViewcontroller的category

</pre><pre name="code" class="objc">#import "UIViewController+AOP.h"
#import <objc/runtime.h>

@implementation UIViewController (AOP)

+ (void)load {
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        Class class = [self class];
        // Class class = object_getClass((id)self);
        swizzleMethod(class, @selector(viewDidLoad), @selector(aop_viewDidLoad));
    });
}
void swizzleMethod(Class class, SEL originalSelector, SEL swizzledSelector)   {
    Method originalMethod = class_getInstanceMethod(class, originalSelector);
    Method swizzledMethod = class_getInstanceMethod(class, swizzledSelector);
    BOOL didAddMethod =
    class_addMethod(class,originalSelector,method_getImplementation(swizzledMethod),method_getTypeEncoding(swizzledMethod));
    if (didAddMethod) {
        class_replaceMethod(class,swizzledSelector,method_getImplementation(originalMethod),method_getTypeEncoding(originalMethod));
    } else {
        method_exchangeImplementations(originalMethod, swizzledMethod);
    }
}

- (void)aop_viewDidLoad {
    [self aop_viewDidLoad];
    
}