method-swizzling-oc

method-swizzling-oc

+ (void)ls_methodSwizzlingWithOriginalSelector:(SEL)originalSelector swizzledSelector:(SEL)swizzledSelector {
    Class class = [self class];
    
    Method originalMethod = class_getInstanceMethod(class, originalSelector);
    Method swizzledMethod = class_getInstanceMethod(class, swizzledSelector);
    
    // When swizzling a class method, use the following:
    // Class class = object_getClass((id)self);
    // ...
    // Method originalMethod = class_getClassMethod(class, originalSelector);
    // Method swizzledMethod = class_getClassMethod(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)load {
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        [self ls_methodSwizzlingWithOriginalSelector:@selector(scrollViewDidScroll:) swizzledSelector:@selector(ls_scrollViewDidScroll:)];
        [self ls_methodSwizzlingWithOriginalSelector:@selector(scrollViewWillBeginDragging:) swizzledSelector:@selector(ls_scrollViewWillBeginDragging:)];
    });
}