UIView的autoresizingMask属性

typedef NS_OPTIONS(NSUInteger, UIViewAutoresizing) {
//不会随父视图的改变而改变
    UIViewAutoresizingNone                 = 0,

//自动调整view与父视图左边距，以保证右边距不变,宽度不变
    UIViewAutoresizingFlexibleLeftMargin   = 1 << 0,

//自动调整view的宽度，保证左边距和右边距不变
    UIViewAutoresizingFlexibleWidth        = 1 << 1,

//自动调整view与父视图右边距，以保证左边距不变，宽度不变
    UIViewAutoresizingFlexibleRightMargin  = 1 << 2,

//自动调整view与父视图上边距，以保证下边距不变，高度不变
    UIViewAutoresizingFlexibleTopMargin    = 1 << 3,

//自动调整view的高度，以保证上边距和下边距不变
    UIViewAutoresizingFlexibleHeight       = 1 << 4,

//自动调整view与父视图的下边距，以保证上边距不变，高度不变
    UIViewAutoresizingFlexibleBottomMargin = 1 << 5