将 CGGradient 添加为 UILabel 的子图层会隐藏标签的文本

Question

我想添加渐变作为标签的背景。我使用以下代码来实现这一目标。但问题是，虽然标签上出现渐变颜色，但文本不可见。请帮忙

lblPatientDetail.text=PatientsDetails;

lblPatientDetail.textColor=[UIColor blackColor];  

CAGradientLayer *gradient = [CAGradientLayer layer];
gradient.frame = lblPatientDetail.bounds;
gradient.colors = [NSArray arrayWithObjects:(id)[[UIColor whiteColor] CGColor],(id)[[UIColor colorWithRed:255/255.0 green:239/255.0 blue:215/255.0 alpha:1.0] CGColor],nil];  

[lblPatientDetail.layer addSublayer:gradient];

lblPatientDetail.backgroundColor=[UIColor clearColor];

Answer 1

向 UILabel 插入子图层会隐藏文本，因此获得所需内容的最佳方法是将标签和渐变图层添加到 UIView。

UIView *gradientLabelView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 100, 30)];

CAGradientLayer *gradient = [CAGradientLayer layer];
gradient.frame = gradientLabelView.bounds;
gradient.colors = [NSArray arrayWithObjects:(id)[[UIColor whiteColor] CGColor],(id)[[UIColor colorWithRed:255/255.0 green:239/255.0 blue:215/255.0 alpha:1.0] CGColor],nil];

[gradientLabelView.layer addSublayer:gradient];

lblPatientDetail.frame = gradientLabelView.bounds;
lblPatientDetail.backgroundColor = [UIColor clearColor];
[gradientLabelView addSubview:lblPatientDetail];

[self addSubview:gradientLabelView];

Answer 2

在 UIView 中使用 UILabel 的建议答案是有效的。显然，在给背景提供渐变颜色背景后，UILabels 不能在其中包含文本...不知道为什么...

但是这是解决方案的完整代码...希望这对某人有帮助:)

UIView *EnvironmentalsLabelView = [[UIView alloc] initWithFrame:CGRectMake(0, 300, 320, 20)];
CAGradientLayer *gradient = [CAGradientLayer layer];
gradient.frame = EnvironmentalsLabelView.bounds;
gradient.colors = [NSArray arrayWithObjects:(id)[[UIColor darkGrayColor]CGColor], (id)[[UIColor blackColor]CGColor], nil];
[EnvironmentalsLabelView.layer insertSublayer:gradient atIndex:0];
[scroller addSubview:EnvironmentalsLabelView];

UILabel *EnviornmentalsLabelText = [[UILabel alloc] initWithFrame:EnvironmentalsLabelView.bounds];
[EnviornmentalsLabelText setFont:[UIFont fontWithName:@"Arial-BoldMT" size:12.0f]];
EnviornmentalsLabelText.textAlignment = NSTextAlignmentCenter;
EnviornmentalsLabelText.backgroundColor = [UIColor clearColor];
EnviornmentalsLabelText.text = @"Environmental Benefits";
[EnvironmentalsLabelView addSubview:EnviornmentalsLabelText];

快乐编码！ ！

Answer 3

还要再思考一下正确答案。
如果您使用自动布局来放置自定义视图，您可能会遇到此问题 - http://prntscr.com/5tj7bx

因此，您的视图的大小与 subView - UILabel 和 subLayer - 渐变层不同。

我通过添加一种方法解决了这个问题

class wResultView: UIView {
var label = UILabel()
var gradientLayer = CAGradientLayer()

override func layoutSubviews() {
    gradientLayer.frame = self.bounds
    label.frame = self.bounds
}
......

Answer 4

最简单的解决方案。

这是苹果的一个巨大错误，他们从来没有修复过20个？年。

要解决此问题，只需在顶部添加另一个 UILabel 并传递“.text”设置即可。

class TrickLabel: UIILabel {
    override var text: String? {
        didSet {
            _label.text = text
        }
    }
    private lazy var bg: CAGradientLayer = {
        let l = CAGradientLayer()
        l.startPoint = CGPoint(x: 0.5, y: 0)
        l.endPoint = CGPoint(x: 0.5, y: 1)
        l.locations = [-1, 2]
        l.colors = [UIColor.cyan,UIColor.yellow].compactMap{$0.cgColor}
        layer.insertSublayer(l, at: 0) // NOTE, MUST USE INSERT NOT ADD
        return l
    }()
    private lazy var _label: UILabel = {
        let v = UILabel.Typical
        v.backgroundColor = .clear
        v.font = blah
        addSubview(v)
        v.bindEdgesToSuperview()
        return v
    }()
    override func layoutSubviews() {
        super.layoutSubviews()
        bg.frame = bounds
        _ = _label
    }
}

如果有必要，您还可以“传递”例如字体、文本颜色等。

就是这么简单。 TrickLabel 的工作方式与 UILabel 完全相同，您可以像平常一样说 .text = "blah" 等。

Answer 5

意味着创建 UIView 的解决方案对于常规使用来说不太方便。让我为此建议一个可重用的解决方案。

import UIKit

@IBDesignable
class GradientTextLabel: UILabel {
    // MARK: - Public vars
    @IBInspectable var startColor: UIColor = .red { didSet { setNeedsDisplay() } }
    @IBInspectable var midColor: UIColor = .orange { didSet { setNeedsDisplay() } }
    @IBInspectable var endColor: UIColor = .yellow { didSet { setNeedsDisplay() } }
    @IBInspectable var vertical = false { didSet { setNeedsDisplay() } }
    
    // MARK: - Lifecycle methods
    override func layoutSubviews() {
        super.layoutSubviews()
        
        let gradient = getGradientLayer(bounds: bounds)
        textColor = gradientColor(bounds: bounds, gradientLayer: gradient)
    }
    
    override func prepareForInterfaceBuilder() {
        setNeedsDisplay()
    }
    
    // MARK: - Private methods
    private func getGradientLayer(bounds : CGRect) -> CAGradientLayer{
        let gradient = CAGradientLayer()
        gradient.frame = bounds
        gradient.colors = [startColor.cgColor, midColor.cgColor, endColor.cgColor]
        
        if vertical {
            gradient.startPoint = CGPoint(x: 0.5, y: 0.0)
            gradient.endPoint = CGPoint(x: 0.5, y: 1.0)
        } else {
            gradient.startPoint = CGPoint(x: 0.0, y: 0.5)
            gradient.endPoint = CGPoint(x: 1.0, y: 0.5)
        }
        
        return gradient
    }
    
    private func gradientColor(bounds: CGRect, gradientLayer :CAGradientLayer) -> UIColor? {
        UIGraphicsBeginImageContext(gradientLayer.bounds.size)
        //create UIImage by rendering gradient layer.
        gradientLayer.render(in: UIGraphicsGetCurrentContext()!)
        let image = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        
        //get gradient UIcolor from gradient UIImage
        return UIColor(patternImage: image!)
    }
}

Answer 6

您可以在 UILabel 中添加 UILabel
像这样。

class GradientLabel: UILabel {  

    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)

        self.clipsToBounds = true
        DispatchQueue.main.async {
            self.applyGradient(with: Color.gradientColor, gradient: GradientOrientation.topLeftBottomRight)
            self.textColor = UIColor.white
        }
        DispatchQueue.main.asyncAfter(deadline: DispatchTime.now() + 0.1) {

            let label = UILabel(frame: CGRect(x: 0, y: 0, width: self.frame.size.width, height: self.frame.size.height))
            label.text = self.text
            label.font = self.font
            label.textColor = self.textColor
            label.textAlignment = self.textAlignment
            self.text = ""
            self.addSubview(label)
        }
    }
}

extension UIView {

    func applyGradient(with colours: [UIColor], locations: [NSNumber]? = nil) {
        let gradient = CAGradientLayer()
        gradient.frame = self.bounds
        gradient.colors = colours.map { $0.cgColor }
        gradient.locations = locations
        self.layer.insertSublayer(gradient, at: 0)
    }

    func applyGradient(with colours: [UIColor], gradient orientation: GradientOrientation) {
        let gradient = CAGradientLayer()
        gradient.frame = self.bounds
        gradient.colors = colours.map { $0.cgColor }
        gradient.startPoint = orientation.startPoint
        gradient.endPoint = orientation.endPoint
        self.layer.insertSublayer(gradient, at: 0)
    }
}

Answer 7

我认为你可以通过调整上面代码中的 alpha 值来创建渐变颜色。

gradient.colors = [NSArray arrayWithObjects:(id)[[UIColor whiteColor] CGColor],(id)[[UIColor colorWithRed:255/255.0 green:239/255.0 blue:215/255.0 alpha:0.1] CGColor],nil];

通过这样做我能够获得渐变效果。