forwardingTargetForSelector用于对指定的selector的截获，然后转换成自己的selector，可以在NSObject子类中重载，如：

- (id)forwardingTargetForSelector:(SEL)aSelector
 {
     if (aSelector == @selector(uppercaseString))
     {
         return@"hello world";
     }
 }

- (id)forwardingTargetForSelector:(SEL)aSelector{
    NSString * selectorName = NSStringFromSelector(aSelector);
    if ([selectorName hasPrefix:@"draw"]) {
        [self apply];
    }
    return _component;
}

对此可以联系到swizzle，想想两者的不同以及相同点，能否达到一致的效果