先说问题

最近在适配iOS13 有个Dark Mode的暗黑模式, 为了适配这个模式不得不在UIView和UIViewController以及UIWindow中复写如下方法

- (void)traitCollectionDidChange:(UITraitCollection *)previousTraitCollection {
    [super traitCollectionDidChange:previousTraitCollection];
}

这里有个UITraitCollection的类以前从来没有仔细研究,今天详细研究一下.

Trait 特性特点

显然这个类是一个UIKit中用于处理苹果手机的一些特性的储存与UI相关的配置, 大家有没有想过如果你在iOS修改通用中的某些系统设置,比如(下图) 对比度、全局字体大小,这个我们开发人员怎么处理.

[站外图片上传中...(image-f50eec-1568792236158)]

这些系统的特性修改就放到这个UITraitCollection中,这个类也就是我们经常在VC和View中经常用到而大家往往容易忽略的,下面简单记录一下这些特性都有哪些

UITraitCollection API介绍

判断当前设备时 iPhone/iPad/tv/carPlay 的配置

+ (UITraitCollection *)traitCollectionWithUserInterfaceIdiom:(UIUserInterfaceIdiom)idiom;
@property (nonatomic, readonly) UIUserInterfaceIdiom userInterfaceIdiom; // unspecified: UIUserInterfaceIdiomUnspecified

关于布局方向的配置

+ (UITraitCollection *)traitCollectionWithLayoutDirection:(UITraitEnvironmentLayoutDirection)layoutDirection API_AVAILABLE(ios(10.0));
@property (nonatomic, readonly) UITraitEnvironmentLayoutDirection layoutDirection API_AVAILABLE(ios(10.0)); // unspecified: UITraitEnvironmentLayoutDirectionUnspecified

图片 Scale 的配置

+ (UITraitCollection *)traitCollectionWithDisplayScale:(CGFloat)scale;
@property (nonatomic, readonly) CGFloat displayScale; // unspecified: 0.0

布局 Size Class 的配置

+ (UITraitCollection *)traitCollectionWithHorizontalSizeClass:(UIUserInterfaceSizeClass)horizontalSizeClass;
@property (nonatomic, readonly) UIUserInterfaceSizeClass horizontalSizeClass; // unspecified: UIUserInterfaceSizeClassUnspecified
+ (UITraitCollection *)traitCollectionWithVerticalSizeClass:(UIUserInterfaceSizeClass)verticalSizeClass;
@property (nonatomic, readonly) UIUserInterfaceSizeClass verticalSizeClass; // unspecified: UIUserInterfaceSizeClassUnspecified

Force Touch 是否可用的配置

+ (UITraitCollection *)traitCollectionWithForceTouchCapability:(UIForceTouchCapability)capability API_AVAILABLE(ios(9.0));
@property (nonatomic, readonly) UIForceTouchCapability forceTouchCapability API_AVAILABLE(ios(9.0)); // unspecified: UIForceTouchCapabilityUnknown

全局字体大小的配置

+ (UITraitCollection *)traitCollectionWithPreferredContentSizeCategory:(UIContentSizeCategory)preferredContentSizeCategory API_AVAILABLE(ios(10.0));
@property (nonatomic, copy, readonly) UIContentSizeCategory preferredContentSizeCategory API_AVAILABLE(ios(10.0)); // unspecified: UIContentSizeCategoryUnspecified

色域的配置

+ (UITraitCollection *)traitCollectionWithDisplayGamut:(UIDisplayGamut)displayGamut API_AVAILABLE(ios(10.0));
@property (nonatomic, readonly) UIDisplayGamut displayGamut API_AVAILABLE(ios(10.0)); // unspecified: UIDisplayGamutUnspecified

是否开启高对比度的配置

+ (UITraitCollection *)traitCollectionWithAccessibilityContrast:(UIAccessibilityContrast)accessibilityContrast API_AVAILABLE(ios(13.0), tvos(13.0)) API_UNAVAILABLE(watchos);
@property (nonatomic, readonly) UIAccessibilityContrast accessibilityContrast API_AVAILABLE(ios(13.0), tvos(13.0)) API_UNAVAILABLE(watchos); // unspecified: UIAccessibilityContrastUnspecified

全局字重的配置

+ (UITraitCollection *)traitCollectionWithLegibilityWeight:(UILegibilityWeight)legibilityWeight API_AVAILABLE(ios(13.0), tvos(13.0), watchos(6.0));
@property (nonatomic, readonly) UILegibilityWeight legibilityWeight API_AVAILABLE(ios(13.0), tvos(13.0), watchos(6.0)); // unspecified: UILegibilityWeightUnspecified

主题的配置

+ (UITraitCollection *)traitCollectionWithUserInterfaceStyle:(UIUserInterfaceStyle)userInterfaceStyle API_AVAILABLE(tvos(10.0)) API_AVAILABLE(ios(12.0)) API_UNAVAILABLE(watchos);
@property (nonatomic, readonly) UIUserInterfaceStyle userInterfaceStyle API_AVAILABLE(tvos(10.0)) API_AVAILABLE(ios(12.0)) API_UNAVAILABLE(watchos); // unspecified: UIUserInterfaceStyleUnspecified

如何获取 UITraitCollection

UITraitCollection本身是一个配置的集合，每个 UIView/UIViewController都有自己的 UITraitCollection对象，并将自己的UITraitCollection传递给子UIView/UIViewController作为默认值。

可以通过 UIView/UIViewController的属性 traitCollection 获取到当前视图的 UITraitCollection 对象

- (void)viewDidLoad {
    [super viewDidLoad];
    self.traitCollection //拿到当前得
}

可以通过子类重写如下方法的方式监控 traitCollection 属性的变化

- (void)traitCollectionDidChange:(UITraitCollection *)previousTraitCollection {
    [super traitCollectionDidChange:previousTraitCollection];
}

获取全局的UITraitCollection

[UITraitCollection currentTraitCollection];

技巧

如果要在UIViewController中更新状态栏当设置完style的时候可以调用

[self setNeedsStatusBarAppearanceUpdate];

总结

通过简单的学习UITraitCollection又深刻学习了一下这个类

对于以上技术点，有更好的理解，想更好的探讨，可以进入iOS技术圈，一起探讨学习
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UITraitCollection详解