参考网页：http://segmentfault.com/a/1190000002420095

写的真不错。赞

横向滑动的手势操作则是这两行代码：

let panGestureRecognizer = UIPanGestureRecognizer(target: self,action: "handlePanGesture:")
centerNavigationController.view.addGestureRecognizer(panGestureRecognizer)

handlePanGesture 处理了滑动手势：

func handlePanGesture(recognizer: UIPanGestureRecognizer) {
    // 判断是否从左向右
    let gestureIsDraggingFromLeftToRight = (recognizer.velocityInView(view).x > 0)

    switch(recognizer.state) {

    // 刚刚开始滑动
    case .Began:
        // 如果刚刚开始滑动的时候还处于主页面，则根据左右方向加入侧面菜单
        if (currentState == .BothCollapsed) {
            if (gestureIsDraggingFromLeftToRight) {
                addLeftPanelViewController()
            } else {
                addRightPanelViewController()
            }
        }

    // 如果是正在滑动，则偏移主视图的坐标实现跟随手指位置移动
    case .Changed:
        recognizer.view!.center.x = recognizer.view!.center.x + recognizer.translationInView(view).x
        recognizer.setTranslation(CGPointZero,inView: view)

    // 如果滑动结束
    case .Ended:
        // 判断该左还是该右
        if (leftViewController != nil) {
            let hasMovedGreaterThanHalfway = recognizer.view!.center.x > view.bounds.size.width animateLeftPanel(shouldExpand: hasMovedGreaterThanHalfway) } else if (rightViewController != nil) {
            let hasMovedGreaterThanHalfway = recognizer.view!.center.x < 0
            animateRightPanel(shouldExpand: hasMovedGreaterThanHalfway)
        }
    default:
        break
    }
}