黑暗模式和多窗口/场景

Question

我正在尝试在多场景应用程序中实现 ios13 暗模式。

不幸的是，当我关闭一个场景并将其拖过屏幕边缘时，方法 traitCollectionDidChange 被多次调用，但值总是不同，导致我的 UI 在暗模式和亮模式之间闪烁。

怎么了？

这是我的实现

func traitCollectionDidChange(_ previousTraitCollection: UITraitCollection?) {  
    super.traitCollectionDidChange(previousTraitCollection)  

    print("THEME instance: \(self)")  

    let currentTraitCollection = self.traitCollection  
    var hasUserInterfaceStyleChanged = false  
    hasUserInterfaceStyleChanged = previousTraitCollection.hasDifferentColorAppearanceCompared(to: currentTraitCollection)  

    print("THEME hasUserInterfaceStyleChanged = \(hasUserInterfaceStyleChanged ? "YES" : "NO")")  

    if hasUserInterfaceStyleChanged {  
        let userInterfaceStyle = currentTraitCollection.userInterfaceStyle // Either .unspecified, .light, or .dark  

        switch userInterfaceStyle {  
            case .unspecified:  
                print("THEME UIUserInterfaceStyleUnspecified")  
            case .light:  
                print("THEME UIUserInterfaceStyleLight")  
            case .dark:  
                print("THEME UIUserInterfaceStyleDark")  
            }  
    } else {  
        print("THEME NOT CHANGED")  
    }  

}

这是控制台中记录的语句

当新场景出现时...

THEME instance: <MainControllerViewController: 0x117e55910>  
THEME hasUserInterfaceStyleChanged = YES  
THEME UIUserInterfaceStyleLight

当添加的场景消失时...

THEME instance: <MainControllerViewController: 0x117e55910>  
THEME hasUserInterfaceStyleChanged = YES  
THEME UIUserInterfaceStyleDark  
THEME instance: <MainControllerViewController: 0x117e55910>  
THEME hasUserInterfaceStyleChanged = YES  
THEME UIUserInterfaceStyleLight  
THEME instance: <MainControllerViewController: 0x117e55910>  
THEME hasUserInterfaceStyleChanged = NO  
THEME NOT CHANGED  
THEME instance: <MainControllerViewController: 0x117e55910>  
THEME hasUserInterfaceStyleChanged = YES  
THEME UIUserInterfaceStyleDark  
THEME instance: <MainControllerViewController: 0x117e55910>  
THEME hasUserInterfaceStyleChanged = YES  
THEME UIUserInterfaceStyleLight

与此同时，我没有更改为暗模式（始终亮）...所以我希望主题不会更改。

Answer 1

我一直在努力解决同样的问题，我找到的解决方案在 SceneDelegate.

一个UIScene有多个状态：

.foregroundActive
.foregroundInactive
.background
.unattached

当您在幻灯片中调整 windows 大小时，或者在这种情况下，从幻灯片中删除一个幻灯片时，每个幻灯片都会调用 traitCollectionDidChange。这意味着您正在为处于 .background、.foregroundInactive 和 .unattached 状态的场景更新 userInterfaceStyle。这就是导致闪烁的原因。

解决方案是不使用 traitCollectionDidChange，而是使用 SceneDelegate 中名为 windowScene(_:didUpdate:interfaceOrientation:traitCollection:) 的委托方法。

根据 Apple's docs 这个方法：

Notifies you when the size, orientation, or traits of a scene change.

这样做的额外好处是我们可以在更新userInterfaceStyle之前检查场景的.activationState。

    func windowScene(_ windowScene: UIWindowScene, didUpdate previousCoordinateSpace: UICoordinateSpace, interfaceOrientation previousInterfaceOrientation: UIInterfaceOrientation, traitCollection previousTraitCollection: UITraitCollection) {

          let currentTraitCollection = windowScene.traitCollection

          if windowScene.activationState == .foregroundActive {
             if currentTraitCollection.userInterfaceStyle != previousTraitCollection.userInterfaceStyle {
                 if currentTraitCollection.userInterfaceStyle == .light {
                     //update to light theme
                 } else {
                     //update to dark theme
                 }
             }
         }
     }

黑暗模式和多窗口/场景

Darkmode and multiwindows / scenes

uitraitcollection

ios13

ios-darkmode