UIView中有个属性是autoresizingMask，该属性是用来控制控件的自适应。
UIViewAutoresizingNone
= 0,
UIViewAutoresizingFlexibleLeftMargin = 1
<< 0,
UIViewAutoresizingFlexibleWidth
= 1 <<
1,
UIViewAutoresizingFlexibleRightMargin = 1 <<
2,
UIViewAutoresizingFlexibleTopMargin = 1 <<
3,
UIViewAutoresizingFlexibleHeight = 1
<< 4,
UIViewAutoresizingFlexibleBottomMargin = 1 <<
5
UIViewAutoresizingNone：控件相对于父视图坐标值不变；
UIViewAutoresizingFlexibleWidth：控件的宽度随着父视图的宽度按比例改变；
例如：label宽度为100，屏幕的宽度为320。当屏幕宽度为480时，label宽度变为100*480/320
UIViewAutoresizingFlexibleHeight：与UIViewAutoresizingFlexibleWidth相同
UIViewAutoresizingFlexibleLeftMargin：到屏幕左边的距离随着父视图的宽度按比例改变；
例如：CGRectMake(50, 100, 200, 40)]; 当屏幕的宽度为320，x为50；当屏幕宽度为480时，labelx坐标变为 50*480/320。控件坐标变为 CGRectMake(75, 100, 200, 40)];
UIViewAutoresizingFlexibleRightMargin、UIViewAutoresizingFlexibleTopMargin、UIViewAutoresizingFlexibleBottomMargin与UIViewAutoresizingFlexibleLeftMargin类似