横竖屏事件响应（viewWillLayoutSubviews和通知）两种方式
http://blog.csdn.net/nogodoss/article/details/17246489
一，NSLayoutConstraint API
1，constraintsWithVisualFormat:
+ (NSArray *)constraintsWithVisualFormat:(NSString *)format options:(NSLayoutFormatOptions)opts metrics:(NSDictionary *)metrics views:(NSDictionary *)views;
参数介绍:
format:此参数为你的vfl语句，比如:@"H:|-[button]-|"
水平方向 H: 垂直方向 V:
Views [view] SuperView |
关系 >=,==,<=
空间,间隙 -
优先级 @value
opts:枚举参数，默认写0，具体跟据你所实现的需求去选择你想要的枚举
metrics:这里是一个字典，当在format中使用了动态数据比如上现这句:@"H:|-[button(==width)]-|",表示这个button的宽度为width,那么这个参数去哪里找呢？就是在这个字典里面找到key对就的值，如果没有找到这个值，app就会crash.
views:顾名思义，这是传所有你在vfl中使用到的view，那在上面这句例子中的应该怎么传呢？结果是这样的：NSDictionaryOfVariableBindings(button).如果你使用到了多个view，就可以这样NSDictionaryOfVariableBindings(button,button1,button3...),这个名字也要跟参数format中的一一对应，缺一不可.
2, addConstraint:
- (void)addConstraint:(NSLayoutConstraint *)constraint NS_AVAILABLE_IOS(6_0); // This method will be deprecated in a future release and should be avoided. Instead, set NSLayoutConstraint's active property to YES.
- (void)addConstraints:(NSArray *)constraints NS_AVAILABLE_IOS(6_0); // This method will be deprecated in a future release and should be avoided. Instead use +[NSLayoutConstraint activateConstraints:].
- (void)removeConstraint:(NSLayoutConstraint *)constraint NS_AVAILABLE_IOS(6_0); // This method will be deprecated in a future release and should be avoided. Instead set NSLayoutConstraint's active property to NO.
- (void)removeConstraints:(NSArray *)constraints NS_AVAILABLE_IOS(6_0); // This method will be deprecated in a future release and should be avoided. Instead use +[NSLayoutConstraint deactivateConstraints:].
eg:
3,
动态计算UITableViewCell高度详解
http://www.ifun.cc/blog/2014/02/21/dong-tai-ji-suan-uitableviewcellgao-du-xiang-jie/#md-5