panning

- (void)updateTopViewHorizontalCenterWithRecognizer:(UIPanGestureRecognizer *)recognizer {
    CGFloat translationX  = [recognizer translationInView:self.slidingViewController.view].x;
    CGFloat velocityX     = [recognizer velocityInView:self.slidingViewController.view].x;

    switch (recognizer.state) {
        case UIGestureRecognizerStateBegan: {
            BOOL isMovingRight = velocityX > 0;

            if (self.slidingViewController.currentTopViewPosition == ECSlidingViewControllerTopViewPositionCentered && isMovingRight) {
                [self.slidingViewController anchorTopViewToRightAnimated:YES];
            } else if (self.slidingViewController.currentTopViewPosition == ECSlidingViewControllerTopViewPositionCentered && !isMovingRight) {
                [self.slidingViewController anchorTopViewToLeftAnimated:YES];
            } else if (self.slidingViewController.currentTopViewPosition == ECSlidingViewControllerTopViewPositionAnchoredLeft) {
                [self.slidingViewController resetTopViewAnimated:YES];
            } else if (self.slidingViewController.currentTopViewPosition == ECSlidingViewControllerTopViewPositionAnchoredRight) {
                [self.slidingViewController resetTopViewAnimated:YES];
            }

            break;
        }
        case UIGestureRecognizerStateChanged: {
            if (!self.positiveLeftToRight) translationX = translationX * -1.0;
            CGFloat percentComplete = (translationX / self.fullWidth);
            if (percentComplete < 0) percentComplete = 0;
            [self updateInteractiveTransition:percentComplete];
            break;
        }
        case UIGestureRecognizerStateEnded:
        case UIGestureRecognizerStateCancelled: {
            BOOL isPanningRight = velocityX > 0;

            if (self.coordinatorInteractionEnded) self.coordinatorInteractionEnded((id<UIViewControllerTransitionCoordinatorContext>)self.slidingViewController);

            if (isPanningRight && self.positiveLeftToRight) {
                [self finishInteractiveTransition];
            } else if (isPanningRight && !self.positiveLeftToRight) {
                [self cancelInteractiveTransition];
            } else if (!isPanningRight && self.positiveLeftToRight) {
                [self cancelInteractiveTransition];
            } else if (!isPanningRight && !self.positiveLeftToRight) {
                [self finishInteractiveTransition];
            }

            break;
        }
        default:
            break;
    }
}