暗黑模式（黑暗模式，深色模式）适配

• 全局关闭

打开Info.plist 项目配置文件，添加UIUserInterfaceStyle字段，key类型为String， 其value值设置为 Light模式。

• 部分关闭

iOS13之后UIViewController与UIView 都新增一个属性 overrideUserInterfaceStyle。该属性设置后，会影响视图控制器和子视图控制器以及父视图和子视图，但不会影响application和present出的视图控制器。

/* Set `overrideUserInterfaceStyle` to cause this view controller and its children to have a* specific `UIUserInterfaceStyle`. This does not affect the application or any parent view controllers.*/
@property (nonatomic) UIUserInterfaceStyle overrideUserInterfaceStyle API_AVAILABLE(tvos(13.0), ios(13.0)) API_UNAVAILABLE(watchos); // Defaults to UIUserInterfaceStyleUnspecified

• 适配暗黑模式

颜色适配

• UIColor 动态颜色systemBackgroundColor、labelColor、systemGray2Color等，自己可以试试切换模式后会有什么效果。

    if (@available(iOS 13.0, *)) {self.view.backgroundColor = [UIColor systemBackgroundColor];} else {// Fallback on earlier versionsself.view.backgroundColor = [UIColor whiteColor];}

• UIColor的colorWithDynamicProvider和initWithDynamicProvider和resolvedColorWithTraitCollection三个方法。

    if (@available(iOS 13.0, *)) {col_lineView.backgroundColor = [UIColor colorWithDynamicProvider:^UIColor * _Nonnull(UITraitCollection * _Nonnull traitCollection) {if (traitCollection.userInterfaceStyle == UIUserInterfaceStyleDark) {return [UIColor whiteColor];}else {return [UIColor blackColor];}}];} else {// Fallback on earlier versionscol_lineView.backgroundColor = [UIColor blackColor];}

图片适配

（1）在Assets.xcassets图片资源库里新建一个Image Set

（2）打开侧边栏，找到最后一项，设置Image Set属性Appearance为Any,Dark。

（3）修改图片名称（所有图片名都一样），拖动图片到不同模式下的对应图片资源里，1倍图可以不用

至此大功告成，可以运行看看效果。

监听模式切换

苹果提供了2个方法，一个是监听模式切换的方法，一个是判断当前的TraitCollection和不同的TraitCollection比较，查看是否能显示不同模式

/*! To be overridden as needed to provide custom behavior when the environment's traits change. */
- (void)traitCollectionDidChange:(nullable UITraitCollection *)previousTraitCollection API_AVAILABLE(ios(8.0));

/* Return whether this trait collection, compared to a different trait collection, could show a different appearance* for dynamic colors that are provided by UIKit or are in an asset catalog.* If you need to be aware of when dynamic colors might change, override `traitCollectionDidChange` in your view or view controller,* and use this method to compare `self.traitCollection` with `previousTraitCollection`.** Currently, a change in any of these traits could affect dynamic colors:*    userInterfaceIdiom, userInterfaceStyle, displayGamut, accessibilityContrast, userInterfaceLevel* and more could be added in the future.*/
- (BOOL)hasDifferentColorAppearanceComparedToTraitCollection:(nullable UITraitCollection *)traitCollection API_AVAILABLE(ios(13.0), tvos(13.0)) API_UNAVAILABLE(watchos);

此方法进入后台时会调用2次，每次hasDifferentColorAppearanceComparedToTraitCollection都返回YES。stackoverflow也有此问题

- (void)traitCollectionDidChange:(UITraitCollection *)previousTraitCollection {[super traitCollectionDidChange:previousTraitCollection];if (@available(iOS 13.0, *)) {BOOL isDiffernt = [self.traitCollection hasDifferentColorAppearanceComparedToTraitCollection:previousTraitCollection];if (isDiffernt) {NSLog(@"%ld----------%ld", (long)self.traitCollection.userInterfaceStyle, previousTraitCollection.userInterfaceStyle);}} else {// Fallback on earlier versions}
}