autoresizing代码实现

主要解决父子控件之间的布局关系：

/*
     Flexible 灵活的,*的
    
     typedef NS_OPTIONS(NSUInteger, UIViewAutoresizing) {
     UIViewAutoresizingNone                 = 0,
     UIViewAutoresizingFlexibleLeftMargin   = 1 << 0,
//   左边是*的,右边是固定的(与storyboard中相反)

     UIViewAutoresizingFlexibleWidth        = 1 << 1,
//   宽度是可拉伸的
    
     UIViewAutoresizingFlexibleRightMargin  = 1 << 2,
//    右边是*的,左边是固定的(与storyboard中相反)

     UIViewAutoresizingFlexibleTopMargin    = 1 << 3,
//    顶部是*的,底部是固定的(与storyboard中相反)

     UIViewAutoresizingFlexibleHeight       = 1 << 4,
//   高度是*的(高度是可拉伸的)

     UIViewAutoresizingFlexibleBottomMargin = 1 << 5
//    底部是*的,顶部是固定的(与storyboard中相反)
     };
    
    

     */

    //四周固定，内部*
   redView.autoresizingMask =UIViewAutoresizingFlexibleWidth|UIViewAutoresizingFlexibleHeight;

    //四周*，内部固定  redView.autoresizingMask=UIViewAutoresizingFlexibleTopMargin|UIViewAutoresizingFlexibleLeftMargin|UIViewAutoresizingFlexibleRightMargin|UIViewAutoresizingFlexibleBottomMargin;

    //四周*，内部也*   redView.autoresizingMask=UIViewAutoresizingFlexibleWidth|UIViewAutoresizingFlexibleHeight|UIViewAutoresizingFlexibleTopMargin|UIViewAutoresizingFlexibleLeftMargin|UIViewAutoresizingFlexibleRightMargin|UIViewAutoresizingFlexibleBottomMargin;