我正在尝试在文本上创建渐变,我使用UIGraphics来使用渐变图像来创建它.我遇到的问题是渐变正在重新启动.有谁知道如何缩放渐变以拉伸到文本？
文本在线框上,将被更改几次.有时它会很完美但有时则不是.
渐变应该从黄色变为蓝色但重新开始,请参见下面的照片：
import UIKit
func colourTextWithGrad(label: UILabel) {
UIGraphicsBeginImageContext(label.frame.size)
UIImage(named: "testt.png")?.drawInRect(label.bounds)
let myGradient: UIImage = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()
label.textColor = UIColor(patternImage: myGradient)
}
解决方法
每次标签大小更改时,您都必须重新绘制图像
这是因为图案化的UIColor只能进行平铺.从the documentation开始：
During drawing,the image in the pattern color is tiled as necessary to cover the given area.
因此,当标签的边界发生变化时,您需要自己更改图像大小 – 因为图案图像不支持拉伸.为此,您可以继承UILabel,并覆盖layoutSubviews方法.这样的事情应该达到预期的效果：
class GradientLabel: UILabel {
let gradientImage = UIImage(named:"gradient.png")
override func layoutSubviews() {
guard let grad = gradientImage else { // skip re-drawing gradient if it doesn't exist
return
}
// redraw your gradient image
UIGraphicsBeginImageContext(frame.size)
grad.drawInRect(bounds)
let myGradient = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()
// update text color
textColor = UIColor(patternImage: myGradient)
}
}
虽然值得注意的是我总是喜欢自己画一个渐变 – 因为你可以有更大的灵活性(比如说你想稍后添加另一种颜色).当您以不同的尺寸重绘图像时,图像的质量可能会降低(尽管由于渐变的性质,这应该是相当小的).
您可以通过覆盖UILabel子类的drawRect来简单地绘制自己的渐变.例如：
override func drawRect(rect: CGRect) {
// begin new image context to let the superclass draw the text in (so we can use it as a mask)
UIGraphicsBeginImageContextWithOptions(bounds.size,false,0.0)
do {
// get your image context
let ctx = UIGraphicsGetCurrentContext()
// flip context
CGContextScaleCTM(ctx,1,-1)
CGContextTranslateCTM(ctx,-bounds.size.height)
// get the superclass to draw text
super.drawRect(rect)
}
// get image and end context
let img = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()
// get drawRect context
let ctx = UIGraphicsGetCurrentContext()
// clip context to image
CGContextClipToMask(ctx,bounds,img.CGImage)
// define your colors and locations
let colors = [UIColor.orangeColor().CGColor,UIColor.redColor().CGColor,UIColor.purpleColor().CGColor,UIColor.blueColor().CGColor]
let locs:[CGFloat] = [0.0,0.3,0.6,1.0]
// create your gradient
let grad = CGGradientCreateWithColors(CGColorSpaceCreateDeviceRGB(),colors,locs)
// draw gradient
CGContextDrawLinearGradient(ctx,grad,CGPoint(x: 0,y:bounds.size.height*0.5),CGPoint(x:bounds.size.width,CGGradientDrawingOptions(rawValue: 0))
}
输出：
斯威夫特4&作为子类
class GradientLabel: UILabel {
// MARK: - Colors to create gradient from
@IBInspectable open var gradientFrom: UIColor?
@IBInspectable open var gradientTo: UIColor?
override func draw(_ rect: CGRect) {
// begin new image context to let the superclass draw the text in (so we can use it as a mask)
UIGraphicsBeginImageContextWithOptions(bounds.size,0.0)
do {
// get your image context
guard let ctx = UIGraphicsGetCurrentContext() else { super.draw(rect); return }
// flip context
ctx.scaleBy(x: 1,y: -1)
ctx.translateBy(x: 0,y: -bounds.size.height)
// get the superclass to draw text
super.draw(rect)
}
// get image and end context
guard let img = UIGraphicsGetImageFromCurrentImageContext(),img.cgImage != nil else { return }
UIGraphicsEndImageContext()
// get drawRect context
guard let ctx = UIGraphicsGetCurrentContext() else { return }
// clip context to image
ctx.clip(to: bounds,mask: img.cgImage!)
// define your colors and locations
let colors: [CGColor] = [UIColor.orange.cgColor,UIColor.red.cgColor,UIColor.purple.cgColor,UIColor.blue.cgColor]
let locs: [CGFloat] = [0.0,1.0]
// create your gradient
guard let grad = CGGradient(coloRSSpace: CGColorSpaceCreateDeviceRGB(),colors: colors as CFArray,locations: locs) else { return }
// draw gradient
ctx.drawLinearGradient(grad,start: CGPoint(x: 0,y: bounds.size.height*0.5),end: CGPoint(x:bounds.size.width,options: CGGradientDrawingOptions(rawValue: 0))
}
}
