DataSource / Delegate generic message forwarding

Forward.m

#pragma mark Delegate / data source message forwarding

- (BOOL)respondsToSelector:(SEL)aSelector {
  return ([super respondsToSelector:aSelector] ||
          [self.dataSource respondsToSelector:aSelector] ||
          [self.delegate respondsToSelector:aSelector]);
}

- (void)forwardInvocation:(NSInvocation *)invocation
{
  if ([self.delegate respondsToSelector:[invocation selector]]) {
    [invocation invokeWithTarget:self.delegate];
  }
  else if ([self.dataSource respondsToSelector:[invocation selector]]) {
    [invocation invokeWithTarget:self.dataSource];
  }
  else {
    [super forwardInvocation:invocation];
  }
}

- (NSMethodSignature *)methodSignatureForSelector:(SEL)selector
{
  NSMethodSignature *signature = [super methodSignatureForSelector:selector];
  if (!signature) {
    signature = [(id) self.delegate methodSignatureForSelector:selector];
  }
  if (!signature) {
    signature = [(id) self.dataSource methodSignatureForSelector:selector];
  }
  return signature;
}