uikit——UIView——autoresizing

相關方法

@property(nonatomic) BOOL               autoresizesSubviews; // default is YES. if set, subviews are adjusted according to their autoresizingMask if self.bounds changes
@property(nonatomic) UIViewAutoresizing autoresizingMask;    // simple resize. default is UIViewAutoresizingNone
           

注：parentview設定autoresizesSubviews，subview設定autoresizingMask，parentview.autoresizesSubviews = YES，subview.autoresizingMask才有意義

UIViewAutoresizing

typedef NS_OPTIONS(NSUInteger, UIViewAutoresizing) {
    UIViewAutoresizingNone                 = 0,
    UIViewAutoresizingFlexibleLeftMargin   = 1 << 0,
    UIViewAutoresizingFlexibleWidth        = 1 << 1,
    UIViewAutoresizingFlexibleRightMargin  = 1 << 2,
    UIViewAutoresizingFlexibleTopMargin    = 1 << 3,
    UIViewAutoresizingFlexibleHeight       = 1 << 4,
    UIViewAutoresizingFlexibleBottomMargin = 1 << 5
};
           

x-axis上UIViewAutoresizing可組合值：

UIViewAutoresizingFlexibleLeftMargin   = 1 << 0,
UIViewAutoresizingFlexibleWidth        = 1 << 1,
UIViewAutoresizingFlexibleRightMargin  = 1 << 2,
           

y-axis上UIViewAutoresizing可組合值：

UIViewAutoresizingFlexibleTopMargin    = 1 << 3,
UIViewAutoresizingFlexibleHeight       = 1 << 4,
UIViewAutoresizingFlexibleBottomMargin = 1 << 5
           

原理

subview在父坐标系x-axis上divide 3個portions：left，width，right

• left：subview左邊緣距離父坐标系原點在x-axis上距離，即subview.frame.origin.x，可能為負
• width：subview自身width，即subview.bounds.size.width，恒為正
• right：parentview.bounds.size.width - left - width，可能為負

當parentview.bounds改變(parentview.autoresizesSubviews = YES)，根據subview.autoresizingMask值把parentview的bounds.size.width變化量按比例配置設定到這3個portions上 parentview.bounds.size.width變化量Δwidth = new parentview.bounds.size.width - parentview.bounds.size.width(可能為負) 如果subview.autoresizingMask = UIViewAutoresizingFlexibleLeftMargin | UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleRightMargin，則：

• new left = left + Δwidth * left / (left + width + right)
• new width = width + Δwidth * width / (left + width + right)
• new right = new parentview.bounds.size.width - new left - new width

如果subview.autoresizingMask = UIViewAutoresizingFlexibleLeftMargin | UIViewAutoresizingFlexibleRightMargin，則：

• new left = left + Δwidth * left / (left + right)
• new width = width
• new right = new parentview.bounds.size.width - new left - new width

如果subview.autoresizingMask = UIViewAutoresizingFlexibleLeftMargin，則：

• new left = left + Δwidth * left / left
• new width = width
• new right = new parentview.bounds.size.width - new left - new width

如果subview.autoresizingMask = UIViewAutoresizingNone，則：

• new left = left
• new width = width
• new right = new parentview.bounds.size.width - new left - new width

注：left，width，right，Δwidth都是帶符号運算，當然width恒為正，left，right和Δwidth可能為負，left + width + right恒等于parentview.bounds.size.width subview在父坐标系y-axis上divide 3個portions：top，height，bottom，原理同x-axis，不再贅述

autoresizing局限性

autoresizing是ios為了适應裝置螢幕尺寸發生改變時，盡可能的不改變代碼而能完美适配所引入的一種簡易layout機制，autoresizing核心是同比例縮放，是以适用于裝置螢幕尺寸長寬比相同，随着apple後續引入了不同長寬比裝置，autoresizing突顯了其局限性：

• autoresizing在表示parent view和sub view之間的pos和size關系時能表示的組合非常有限，在x-axis或y-axis一維空間内隻能表示有限的8種(1 + 3 + 3 + 1)組合關系，在x-axis和y-axis二維空間内隻能表示有限的64種(8 * 8)組合關系，而且隻能按某種比例機制，是以不能表示parent view和sub view之間更多更精确的pos和size關系