如何检测iOS 13中的明暗模式更改? [英] How to detect Light\Dark mode change in iOS 13?

问题描述

某些用户界面设置无法自动使用，暗/亮模式更改为UIColor.例如图层中的shadow.因为我需要在暗和亮模式下删除阴影并添加阴影，所以我需要在某处放置updateShadowIfNeeded()函数.我知道如何检测当前的模式:

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")
    }
}

现在，我将函数放在layoutSubviews中，因为每次外观更改时都会调用该函数:

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

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

但是此功能被称为很多.仅当userInterfaceStyle更改时才触发的正确功能是什么?

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

推荐答案

我在 WWDC 2019-会议214 大约在23:30结束.

I found the answer on WWDC 2019 - Session 214 around 23:30.

正如我预期的那样，包括更改颜色时，此函数被调用很多.除了ViewController和presentationController的许多其他功能之外.但是有一些专门设计的功能在所有View代表中都有相似的签名.

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.

看看该会话中的这张图片:

Take a look at this image from that session:

灰色:打电话，但不适合我的问题，绿色:专为此设计

所以我应该调用它并在此函数中检查它:

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()
    }
}

这将确保每次更改仅被调用一次.

This will guarantee to be called just once per change.

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