如何在 XCode 6 中为 UISlider 添加渐变色？

Question

我正在开发一个设计应用程序，其中有一个部分用于通过 RGB 的三个滑块 selecting 颜色。正如我们在 xcode 中看到的那样，我们希望通过 RGB 值 select 颜色，滑块色调颜色是一种渐变颜色，当我们改变滑块时它会发生变化。我想在我的应用程序中使用它。但我不知道该怎么做？

我在博客中找到了这段代码。但对我不起作用。

- (void)setGradientToSlider:(UISlider *)Slider WithColors:(NSArray *)Colors{

    UIView * view = (UIView *)[[Slider subviews]objectAtIndex:0];

    UIImageView * maxTrackImageView = (UIImageView *)[[view subviews]objectAtIndex:0];

    CAGradientLayer * maxTrackGradient = [CAGradientLayer layer];
    CGRect rect = maxTrackImageView.frame;
    rect.origin.x = view.frame.origin.x;

    maxTrackGradient.frame = rect;
    maxTrackGradient.colors = Colors;

    [maxTrackGradient setStartPoint:CGPointMake(0.0, 0.5)];
    [maxTrackGradient setEndPoint:CGPointMake(1.0, 0.5)];

    [[maxTrackImageView layer] insertSublayer:maxTrackGradient atIndex:0];

    /////////////////////////////////////////////////////

    UIImageView * minTrackImageView = (UIImageView *)[[view subviews]objectAtIndex:1];

    CAGradientLayer * minTrackGradient = [CAGradientLayer layer];
    rect = minTrackImageView.frame;
    rect.size.width = maxTrackImageView.frame.size.width;
    rect.origin.x = 0;
    rect.origin.y = 0;

    minTrackGradient.frame = rect;
    minTrackGradient.colors = Colors;

    [minTrackGradient setStartPoint:CGPointMake(0.0, 0.5)];
    [minTrackGradient setEndPoint:CGPointMake(1.0, 0.5)];

    [minTrackImageView.layer insertSublayer:minTrackGradient atIndex:0];

}

如果有任何帮助，我将不胜感激。谢谢

Answer 1

以下是可能的解决方案：

用法：

//array of CGColor objects, color1 and color2 are UIColor objects 
NSArray *colors = [NSArray arrayWithObjects:(id)color1.CGColor, (id)color2.CGColor, nil];
//your UISlider
[slider setGradientBackgroundWithColors:colors];

实施：

在 UISlider 上创建类别：

- (void)setGradientBackgroundWithColors:(NSArray *)colors
{
    CAGradientLayer *trackGradientLayer = [CAGradientLayer layer];
    CGRect frame = self.frame;
    frame.size.height = 5.0; //set the height of slider
    trackGradientLayer.frame = frame;
    trackGradientLayer.colors = colors;
    //setting gradient as horizontal
    trackGradientLayer.startPoint = CGPointMake(0.0, 0.5);
    trackGradientLayer.endPoint = CGPointMake(1.0, 0.5);

    UIImage *trackImage = [[UIImage imageFromLayer:trackGradientLayer] resizableImageWithCapInsets:UIEdgeInsetsZero];
    [self setMinimumTrackImage:trackImage forState:UIControlStateNormal];
    [self setMaximumTrackImage:trackImage forState:UIControlStateNormal];
}

其中 colors 是 CGColor 数组。

我还在 UIImage 上创建了一个类别，它根据图层创建图像，因为您需要一个 UIImage 来设置滑块上的渐变。

+ (UIImage *)imageFromLayer:(CALayer *)layer
{
    UIGraphicsBeginImageContextWithOptions(layer.frame.size, layer.opaque, 0.0);

    [layer renderInContext:UIGraphicsGetCurrentContext()];
    UIImage *outputImage = UIGraphicsGetImageFromCurrentImageContext();

    UIGraphicsEndImageContext();

    return outputImage;
}

Answer 2

虽然它没有给我想要的结果，但对于那些想要尝试的人来说，上面的答案是一个肮脏的 Swift 版本。

func setSlider(slider:UISlider) {

    let tgl = CAGradientLayer()
    let frame = CGRectMake(0, 0, slider.frame.size.width, 5)
    tgl.frame = frame
    tgl.colors = [UIColor.blueColor().CGColor, UIColor.greenColor().CGColor, UIColor.yellowColor().CGColor, UIColor.orangeColor().CGColor, UIColor.redColor().CGColor]
    tgl.startPoint = CGPointMake(0.0, 0.5)
    tgl.endPoint = CGPointMake(1.0, 0.5)

    UIGraphicsBeginImageContextWithOptions(tgl.frame.size, tgl.opaque, 0.0);
    tgl.renderInContext(UIGraphicsGetCurrentContext()!)
    let image = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()

    image.resizableImageWithCapInsets(UIEdgeInsetsZero)

    slider.setMinimumTrackImage(image, forState: .Normal)
    //slider.setMaximumTrackImage(image, forState: .Normal)

}

更新 Swift 4.0

func setSlider(slider:UISlider) {
    let tgl = CAGradientLayer()
    let frame = CGRect.init(x:0, y:0, width:slider.frame.size.width, height:5)
    tgl.frame = frame
    tgl.colors = [UIColor.blue.cgColor, UIColor.green.cgColor, UIColor.yellow.cgColor, UIColor.orange.cgColor, UIColor.red.cgColor]
    tgl.startPoint = CGPoint.init(x:0.0, y:0.5)
    tgl.endPoint = CGPoint.init(x:1.0, y:0.5)

    UIGraphicsBeginImageContextWithOptions(tgl.frame.size, tgl.isOpaque, 0.0);
    tgl.render(in: UIGraphicsGetCurrentContext()!)
    if let image = UIGraphicsGetImageFromCurrentImageContext() {
        UIGraphicsEndImageContext()

        image.resizableImage(withCapInsets: UIEdgeInsets.zero)

        slider.setMinimumTrackImage(image, for: .normal)
    }
}

Answer 3

这是我在大量网络搜索后发现的一种非常有效的方法。所以最好在这里分享它作为一个完整的答案。以下代码是一个 Swift Class，您可以使用它来创建渐变并将其用作 UIView 或 UIImage。

import Foundation
import UIKit

class Gradient: UIView{
    // Gradient Color Array
    private var Colors: [UIColor] = []

    // Start And End Points Of Linear Gradient
    private var SP: CGPoint = CGPoint.zeroPoint
    private var EP: CGPoint = CGPoint.zeroPoint

    // Start And End Center Of Radial Gradient
    private var SC: CGPoint = CGPoint.zeroPoint
    private var EC: CGPoint = CGPoint.zeroPoint

    // Start And End Radius Of Radial Gradient
    private var SR: CGFloat = 0.0
    private var ER: CGFloat = 0.0

    // Flag To Specify If The Gradient Is Radial Or Linear
    private var flag: Bool = false

    // Some Overrided Init Methods
    required init(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
    }

    override init(frame: CGRect) {
        super.init(frame: frame)
    }

    // Draw Rect Method To Draw The Graphics On The Context
    override func drawRect(rect: CGRect) {
        // Get Context
        let context = UIGraphicsGetCurrentContext()

        // Get Color Space
        let colorSpace = CGColorSpaceCreateDeviceRGB()

        // Create Arrays To Convert The UIColor to CG Color
        var colorComponent: [CGColor] = []
        var colorLocations: [CGFloat] = []
        var i: CGFloat = 0.0

        // Add Colors Into The Color Components And Use An Index Variable For Their Location In The Array [The Location Is From 0.0 To 1.0]
        for color in Colors {
            colorComponent.append(color.CGColor)
            colorLocations.append(i)
            i += CGFloat(1.0) / CGFloat(self.Colors.count - 1)
        }

        // Create The Gradient With The Colors And Locations
        let gradient: CGGradientRef = CGGradientCreateWithColors(colorSpace, colorComponent, colorLocations)

        // Create The Suitable Gradient Based On Desired Type
        if flag {
            CGContextDrawRadialGradient(context, gradient, SC, SR, EC, ER, 0)
        } else {
            CGContextDrawLinearGradient(context, gradient, SP, EP, 0)
        }
    }

    // Get The Input Data For Linear Gradient
    func CreateLinearGradient(startPoint: CGPoint, endPoint: CGPoint, colors: UIColor...) {
        self.Colors = colors
        self.SP = startPoint
        self.EP = endPoint
        self.flag = false
    }

    // Get The Input Data For Radial Gradient
    func CreateRadialGradient(startCenter: CGPoint, startRadius: CGFloat, endCenter: CGPoint, endRadius: CGFloat, colors: UIColor...) {
        self.Colors = colors
        self.SC = startCenter
        self.EC = endCenter
        self.SR = startRadius
        self.ER = endRadius
        self.flag = true
    }

    // Function To Convert Gradient To UIImage And Return It
    func getImage() -> UIImage {
        // Begin Image Context
        UIGraphicsBeginImageContext(self.bounds.size)

        // Draw The Gradient
        self.drawRect(self.frame)

        // Get Image From The Current Context
        let image = UIGraphicsGetImageFromCurrentImageContext()

        // End Image Context
        UIGraphicsEndImageContext()

        // Return The Result Gradient As UIImage
        return image
    }
}

Answer 4

对于 Swift 3 并且为了防止滑块缩放最小图像，请在设置其图像时应用此选项。没有必要重新计算滑块的左侧。只有在可以更改渐变颜色的情况下才重新计算。 Max 图像似乎没有缩放，但您可能应该应用相同的设置以保持一致性。不应用插图时，Max 图像略有不同。

slider.setMinimumTrackImage(image?.resizableImage(withCapInsets:.zero), for: .normal)

出于某种原因，它只有在 resizableImage(withCapInsets:.zero) 同时完成时才能正常工作。运行分开的部分不允许图像工作并被缩放。

这是Swift 3中的整个例程：

func setSlider(slider:UISlider) {
    let tgl = CAGradientLayer()
    let frame = CGRect(x: 0.0, y: 0.0, width: slider.bounds.width, height: 5.0 )
    tgl.frame = frame
    tgl.colors = [ UIColor.yellow.cgColor,UIColor.black.cgColor]
    tgl.endPoint = CGPoint(x: 1.0, y:  1.0)
    tgl.startPoint = CGPoint(x: 0.0, y:  1.0)

    UIGraphicsBeginImageContextWithOptions(tgl.frame.size, false, 0.0)
    tgl.render(in: UIGraphicsGetCurrentContext()!)
    let image = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()

    slider.setMaximumTrackImage(image?.resizableImage(withCapInsets:.zero),  for: .normal)
    slider.setMinimumTrackImage(image?.resizableImage(withCapInsets:.zero),  for: .normal)
}

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