Navigation Controller以一个栈的形式维护VC，通过pushViewController入栈，popViewController出栈。
页面分几部分：Navigation bar, Custom Content和Navigation toolbar
1.Navigation bar
1.简单实用
UIBarButtonItem *leftButton = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemAction target:self action:@selector(selectLeftAction:)];
self.navigationItem.leftBarButtonItem = leftButton;
UIBarButtonItem *rightButton = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemAdd target:self action:@selector(selectRightAction:)];
self.navigationItem.rightBarButtonItem = rightButton;
2.还有一些系统提供的自定义风格的button形式，详细内容
3.titleView
titleView可以替换成button，或者SegmentedControl，具体方法参见
2.Navigation toolbar
toolbar使用
hidesBottomBarWhenPushed
http://blog.csdn.net/holydancer/article/details/8097585
