如何检测 iOS 13 中的 LightDark 模式变化?

问题描述

某些 UI 设置无法在暗/亮模式更改为 UIColor 时自动工作.例如 shadow 在图层中.因为我需要在明暗模式下删除和放置阴影，所以我需要在某个地方放置 updateShadowIfNeeded() 函数.我知道如何检测当前的模式:

func dropShadowIfNeeded() {切换 traitCollection.userInterfaceStyle {案例.dark:removeShadow()case .light: dropShadowIfNotDroppedYet()默认值: assertionFailure("Unknown userInterfaceStyle")}}

现在我把这个函数放在 layoutSubviews 中，因为每次外观改变时它都会被调用:

override func layoutSubviews() {super.layoutSubviews()dropShadowIfNeeded()}

但是这个函数被调用很多.仅当 userInterfaceStyle 更改时才触发的正确功能是什么?

解决方案

SwiftUI

在 .colorScheme 键上使用一个简单的环境变量:

struct ContentView:查看{@Environment(.colorScheme) var colorSchemevar主体:一些视图{文本(colorScheme == .dark ?Its Dark":Its. not dark！(Light)")}}

---

UIKit

正如

灰色:打电话但不适合我的问题，绿色:为此而设计

所以我应该调用它并在这个函数中检查它:

override func traitCollectionDidChange(_ previousTraitCollection: UITraitCollection?) {super.traitCollectionDidChange(previousTraitCollection)如果 traitCollection.hasDifferentColorAppearance(比较:previousTraitCollection){dropShadowIfNeeded()}}

这将保证每次更改只调用一次.

如果您只是在寻找样式的初始状态，在此处查看此答案

Some of the UI setups not working automatically with the Dark/Light mode change as the UIColor. For example shadow in layer. As I need to remove and drop shadow in dark and light mode, I need somewhere to put updateShadowIfNeeded() function. I know how to detect what is the mode currently:

func dropShadowIfNeeded() {
    switch traitCollection.userInterfaceStyle {
    case .dark: removeShadow()
    case .light: dropShadowIfNotDroppedYet()
    default: assertionFailure("Unknown userInterfaceStyle")
    }
}

Now I put the function inside the layoutSubviews, since it gets called every time appearance change:

override func layoutSubviews() {
    super.layoutSubviews()
    dropShadowIfNeeded()
}

But this function is getting called A LOT. What is the proper function to trigger only if userInterfaceStyle changed?

解决方案

SwiftUI

With a simple environment variable on the .colorScheme key:

struct ContentView: View {
    @Environment(.colorScheme) var colorScheme

    var body: some View {
        Text(colorScheme == .dark ? "Its Dark" : "Its. not dark! (Light)")
    }
}

---

UIKit

As it described in WWDC 2019 - Session 214 around 23:30.

As I expected, this function is getting called a lot including when colors changing. Along side with many other functions for ViewController and presentationController. But there is some especial function designed for that has a similar signature in all View representers.

Take a look at this image from that session:

Gray: Calling but not good for my issue, Green: Designed for this

So I should call it and check it inside this function:

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

    if traitCollection.hasDifferentColorAppearance(comparedTo: previousTraitCollection) {
        dropShadowIfNeeded()
    }
}

This will guarantee to be called just once per change.

if you are only looking for the initial state of the style, check out this answer here

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