// 1
+ (BOOL)resolveInstanceMethod:(SEL)sel
+ (BOOL)resolveClassMethod:(SEL)sel
// 2
- (id)forwardingTargetForSelector:(SEL)aSelector
// 3
- (NSMethodSignature *)methodSignatureForSelector:(SEL)aSelector;
- (void)forwardInvocation:(NSInvocation *)anInvocation;
原文：http://my.oschina.net/u/734027/blog/425218