视图布局（1）

• 设备方向
• 界面方向
  • tip
• UITraitCollection
  • 相关枚举
    • UIUserInterfaceIdiom
    • UIUserInterfaceSizeClass
  • UITraitEnvironment协议
  • UIContentContainer协议
• Size Class和IB

iOS开发中的方向包含两个：设备方向（Device orientation），界面方向（Interface orientation）

设备方向

也就是手机的方向，对应于枚举UIDeviceOrientation

typedef enum {
UIDeviceOrientationUnknown,
UIDeviceOrientationPortrait, 
UIDeviceOrientationPortraitUpsideDown,
UIDeviceOrientationLandscapeLeft,
UIDeviceOrientationLandscapeRight,
UIDeviceOrientationFaceUp,
UIDeviceOrientationFaceDown 
} UIDeviceOrientation;

LandscapeRight：with the device held upright and the home button on the left side

FaceUp


界面方向

对应于枚举UIInterfaceOrientation

typedef enum : NSInteger {
   UIInterfaceOrientationUnknown            = UIDeviceOrientationUnknown,
   UIInterfaceOrientationPortrait           = UIDeviceOrientationPortrait,
   UIInterfaceOrientationPortraitUpsideDown = UIDeviceOrientationPortraitUpsideDown,
   UIInterfaceOrientationLandscapeLeft      = UIDeviceOrientationLandscapeRight,
   UIInterfaceOrientationLandscapeRight     = UIDeviceOrientationLandscapeLeft 
} UIInterfaceOrientation;

UIInterfaceOrientation和UIDeviceOrientation大致上是对应的，但Lanscape不一样

UIInterfaceOrientationLandscapeLeft      = UIDeviceOrientationLandscapeRight,
UIInterfaceOrientationLandscapeRight     = UIDeviceOrientationLandscapeLeft 

因为当设备处在LanscapeRight时，在调整界面时，实际上是往左旋转。
portrait:

未调整UIInterfaceOrientation

调整UIInterfaceOrientation

（对比调整前，其实界面往左旋转了）

tip

• 可通过获取状态栏的方向来查看界面方向

UIInterfaceOrientation ori = [[UIApplication sharedApplication] statusBarOrientation];

• 可通过NSNotification监听设备旋转事件

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(deviceOrientaitonChange:) name:UIDeviceOrientationDidChangeNotification object:nil];

• 如果重写shouldAutorotate使其返回NO，那么界面不会随着设备旋转，ori的值保持不变
• 当device从UIDeviceOrientationLandscapeRight旋转到UIDeviceOrientationPortraitUpsideDown时，界面方向维持为UIInterfaceOrientationLeft。 

UITraitCollection

UITraitCollection is used to describe iOS interface environment。It contains the following property:

• horizontalSizeClass
• verticalSizeClass
• displayScale(for iPhone6 plus it is 3.0)
• userInterfaceIdiom

相关枚举

UIUserInterfaceIdiom

typedef NS_ENUM(NSInteger, UIUserInterfaceIdiom) {
    UIUserInterfaceIdiomUnspecified = -1,
    UIUserInterfaceIdiomPhone 
    UIUserInterfaceIdiomPad 
    UIUserInterfaceIdiomTV 
};

UIUserInterfaceSizeClass

    UIUserInterfaceSizeClassUnspecified = 0,
    UIUserInterfaceSizeClassCompact     = 1,
    UIUserInterfaceSizeClassRegular     = 2,

UITraitEnvironment协议

• UITraitEnvironment协议中有一个UITraitCollection类型的属性traitCollection，指明interface当前所处环境
• UIScreen, UIWindow, UIViewController, UIPresentationController, UIView都遵循了这个协议
• traitCollectionDidChange:
  • 当interface environment改变的时候，该方法会被调用
  • 结合前面对UIInterfaceOrientation的检查，可以知道只有当设备从Portrait转换到LanscapeRight，从LanscapeLeft转换到Portrait时才会触发该方法的调用（因为其他情况下，界面的方向一直是Lanscape，UITraitCollection也就不会改变）

UIContentContainer协议

所有UIViewController和 UIPresentationController都实现了该协议

• willTransitionToTraitCollection:withTransitionCoordinator:
  • 次方法可用于在UI的整体环境改变后适当调整UI（(usually high level presentation style）
  • 如：a container view controller change the number of child view controller;
  • 再如：普通的view controller可在此方法中调整view hieratchy中的视图约束

Size Class和IB

• Size Classes与Image Asset
  • 在Image Asset中可为某个Image set根据不同的size class添加不同的图片；运行时SDK就将从中挑选对应的Size的图进行替换了
  • 还可以将渲染选项设置为 Template Image，设置不同size下的tintcolor

//AppDlegate
    [UIView appearanceForTraitCollection:[UITraitCollection traitCollectionWithHorizontalSizeClass:UIUserInterfaceSizeClassCompact]].tintColor = [UIColor redColor];
    [UIView appearanceForTraitCollection:[UITraitCollection traitCollectionWithHorizontalSizeClass:UIUserInterfaceSizeClassRegular]].tintColor = [UIColor purpleColor];

• Size Classes与Interface
  • 可控某些控件只出现在某些size中
  • 根据size为控件设置不同的布局约束





感谢：https://onevcat.com/2014/07/ios-ui-unique/
（写得真的很赞）