iOS

Question

我正在尝试为 UILabel 绘制渐变，但它只绘制了我看不到文本的颜色。我从这里看到代码 Whosebug

我的修改：

extension String{
    func gradient(x:CGFloat,y:CGFloat, fontSize:CGFloat)->UIImage{
        let font:UIFont = UIFont.systemFontOfSize(fontSize)
        let name:String = NSFontAttributeName
        let textSize: CGSize = self.sizeWithAttributes([name:font])
        let width:CGFloat = textSize.width         // max 1024 due to Core Graphics limitations
        let height:CGFloat = textSize.height       // max 1024 due to Core Graphics limitations
        UIGraphicsBeginImageContext(CGSizeMake(width, height))
        let context = UIGraphicsGetCurrentContext()
        UIGraphicsPushContext(context!)
        //draw gradient
        let glossGradient:CGGradientRef?
        let rgbColorspace:CGColorSpaceRef?
        let num_locations:size_t = 2
        let locations:[CGFloat] = [ 0.0, 1.0 ]
        let components:[CGFloat] = [(202 / 255.0), (197 / 255.0), (52 / 255.0), 1.0,  // Start color
            (253 / 255.0), (248 / 255.0), (101 / 255.0), 1.0] // End color
        rgbColorspace = CGColorSpaceCreateDeviceRGB()
        glossGradient = CGGradientCreateWithColorComponents(rgbColorspace, components, locations, num_locations)
        let topCenter = CGPointMake(0, 0);
        let bottomCenter = CGPointMake(0, textSize.height);
        CGContextDrawLinearGradient(context, glossGradient, topCenter, bottomCenter, CGGradientDrawingOptions.DrawsBeforeStartLocation)
        UIGraphicsPopContext()
        let gradientImage = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        return  gradientImage
    }
}

和 imageView 的设置

    self.timeLeftIV = UIImageView(frame: CGRectMake(self.pyramidFakeView.frame.origin.x/2-25,0, 100,20))
    self.timeLeftIV.image = "59:48".gradient(timeLeftIV.frame.origin.x, y: timeLeftIV.frame.origin.y, fontSize: 6.0)

代码结果：

Answer 1

添加一个视图，用下面的代码修改绘制矩形。

override func drawRect(rect: CGRect) {
        // Drawing code

        let currentContext = UIGraphicsGetCurrentContext()

        CGContextSaveGState(currentContext);
        let colorSpace = CGColorSpaceCreateDeviceRGB()

        let startColor = UIColor(red: 0.1, green: 0.0, blue: 0.0, alpha: 0.0)
        let startColorComponents = CGColorGetComponents(startColor.CGColor)
        let middleColor = UIColor(red: 0.0, green: 0.0, blue: 0.0, alpha: 0.2)
        let middleColorComponents = CGColorGetComponents(middleColor.CGColor)
        let lowerMiddleColor = UIColor(red: 0.0, green: 0.0, blue: 0.0, alpha: 0.3)
        let lowerMiddleColorComponents = CGColorGetComponents(lowerMiddleColor.CGColor)
        let endColor = UIColor(red: 0.0, green: 0.0, blue: 0.0, alpha: 0.5)
        let endColorComponents = CGColorGetComponents(endColor.CGColor)

        var colorComponents = [startColorComponents[0], startColorComponents[1], startColorComponents[2], startColorComponents[3], middleColorComponents[0], middleColorComponents[1], middleColorComponents[2], middleColorComponents[3], lowerMiddleColorComponents[0], lowerMiddleColorComponents[1], lowerMiddleColorComponents[2], lowerMiddleColorComponents[3], endColorComponents[0], endColorComponents[1], endColorComponents[2], endColorComponents[3]]
        var locations:[CGFloat] = [0.0, 0.6, 0.8, 1.0]
        let gradient = CGGradientCreateWithColorComponents(colorSpace,&colorComponents,&locations,4)
        let startPoint = CGPointMake(0, 0)
        let endPoint = CGPointMake(0, self.bounds.height)
        CGContextAddRect(currentContext, CGRect(x: 0, y: 0, width: self.bounds.width, height: self.bounds.height));
        CGContextClip(currentContext);
        CGContextDrawLinearGradient(currentContext,gradient,startPoint,endPoint, CGGradientDrawingOptions.DrawsBeforeStartLocation)
        CGContextRestoreGState(currentContext)
    }

现在在情节提要中添加一个视图更改 class 到您的渐变 class 并向该视图添加一个标签。

看看它是否适合你。

Answer 2

有一种获取渐变的更简单方法 UIImage。您可以使用 CAGradientLayer。例如：

func yellowGradientImage(bounds:CGRect) -> UIImage
{
    let gradientLayer = CAGradientLayer()
    gradientLayer.colors = [UIColor(red: (202 / 255.0), green: (197 / 255.0), blue: (52 / 255.0), alpha: 1.0).CGColor, UIColor(red: (253 / 255.0), green: (248 / 255.0), blue: (101 / 255.0), alpha: 1.0).CGColor]
    gradientLayer.bounds = bounds
    UIGraphicsBeginImageContextWithOptions(gradientLayer.bounds.size, true, 0.0)
    let context = UIGraphicsGetCurrentContext()
    gradientLayer.renderInContext(context!)
    let image = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()
    return image
}

要将渐变应用于文本，您接下来需要使用 UIColor(patternImage: ...) 作为 textColor 返回的图像。例如：

let label = UILabel()
label.font = UIFont.systemFontOfSize(150.0)
label.text = "HELLO WORLD"
label.sizeToFit()

let image = yellowGradientImage(label.bounds)
label.textColor = UIColor(patternImage: image)

这导致：

swift 3.0:

func yellowGradientImage(bounds:CGRect) -> UIImage
{
    let gradientLayer = CAGradientLayer()
    gradientLayer.colors = [UIColor(red: (202 / 255.0), green: (197 / 255.0), blue: (52 / 255.0), alpha: 1.0).cgColor, UIColor(red: (253 / 255.0), green: (248 / 255.0), blue: (101 / 255.0), alpha: 1.0).cgColor]
    gradientLayer.bounds = bounds
    UIGraphicsBeginImageContextWithOptions(gradientLayer.bounds.size, true, 0.0)
    let context = UIGraphicsGetCurrentContext()
    gradientLayer.render(in: context!)
    let image = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()
    return image!
}

let label = UILabel()
label.font = UIFont.systemFont(ofSize: 150.0)
label.text = "HELLO WORLD"
label.sizeToFit()

let image = yellowGradientImage(bounds: label.bounds)
label.textColor = UIColor(patternImage: image)

iOS - 绘制渐变 - Swift

iOS - Draw gradient - Swift

gradient

draw

uilabel

swift