iOS开发：解决右滑返回上一页功能失效

iOS7以后，默认支持右滑返回上一页，但是，当隐藏navigationBar或是自定义返回按钮时，右滑返回就会失效。解决方法，自己实现interactivePopGestureRecognizer的delegate viewDidLoad:

navigationController?.interactivePopGestureRecognizer!.delegate = self ;

实现UIGestureRecognizerDelegate定义的方法:

func gestureRecognizerShouldBegin(gestureRecognizer: UIGestureRecognizer) -> Bool {
    if (navigationController?.viewControllers.count <= 1 ) {
        return false;
    }
    return true;
}