Cell将检测到，layer不会检测到！例如，您必须手动更新cell中的所有layer适应.

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

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

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I'm checking my existing app to work correctly with the new introduced dark mode feature of ios 13.

Everything seems to work fine, only the cell background in one of my tableViews is not refreshed according the mode (dark / light).

If the app starts in dark mode, the cells also show the correct dark background. If the mode changes while the app is in background, the cell background color is not changed. The cell label switches the color correct.

for the tableview cells i use the following func for a gradient:

func gradient(frame:CGRect) -> CAGradientLayer { 

    let gradColor1 = UIColor(named: "gradientBright")!
    let gradColor2 = UIColor(named: "gradientDark")!

    let layer = CAGradientLayer()
    layer.frame = frame
    layer.startPoint = CGPoint(x: 0.5, y: 0)
    layer.endPoint = CGPoint(x: 0.5, y: 1)
    layer.colors = [
        gradColor1.cgColor,
        gradColor2.cgColor
    ]
    layer.shadowOpacity = 0.7
    layer.shadowRadius = 10.0
    return layer
}

i add the gradient background to the table cells in

override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {

with the following code

cell.layer.insertSublayer(gradient(frame: cell.bounds), at: 0)

Any idea, why only the gradient func does not seem to get the correct colors after a mode change happened while app active or in background?

Regards

Cell will detect, layer will not! You must manually update all layer adaptations in the cell for example.

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

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

More description here