使用自动布局为 UIView 应用渐变背景

Question

我扩展了 UIView 以添加一个 addGradientWithColor() 方法来获取渐变背景：

 extension UIView {
   func addGradientWithColor() {
     let gradient = CAGradientLayer()
     gradient.frame = self.bounds
     gradient.colors = [gradientEndColor.CGColor,  gradientStartColor.CGColor]
     gradient.startPoint = CGPointMake(1,0)
     gradient.endPoint = CGPointMake(0.2,1)
    self.layer.insertSublayer(gradient, atIndex: 0)
  } }

我的问题是当我运行横向模式时，UIView 没有拉伸

override func viewDidLayoutSubviews() {
    super.viewDidLayoutSubviews()
    self.view.addGradientWithColor() }

我尝试调用 viewDidLayoutSubviews() 但它无法正常工作

这是屏幕截图：

删除 viewDidLayoutSubviews() 后

Answer 1

图层不会自行调整大小。要解决此问题，您应该更改图层框架。这是一种可以实现的方式：

override func viewDidLayoutSubviews() {
    super.viewDidLayoutSubviews()
    //Update you're layer based on the new frame
    self.view.addGradientWithColor()

 }

Answer 2

您可以保存对图层的引用，并在视图 layoutSublayersOfLayer 方法中调整它的框架。这可以在 UIView 子类中外包：

class GradientView: UIView {

private let gradient : CAGradientLayer = CAGradientLayer()

/**
 displays a gradient on the view
 */
func addGradient() {

    self.gradient.frame     = self.bounds
    self.gradient.colors    = [gradientEndColor.CGColor, gradientStartColor.CGColor]
    gradient.startPoint     = CGPointMake(1,0)
    gradient.endPoint       = CGPointMake(0.2,1)        
    self.layer.insertSublayer(self.gradient, atIndex: 0)
}

/**
 resizes the gradient with the view size
 */
override func layoutSublayers(of layer: CALayer) {
    super.layoutSublayers(of: layer)
    self.gradient.frame = self.bounds
}
}

Answer 3

您可以子类化 UIView 并在添加渐变的地方重写 drawRect 方法。

已更新为 Swift 4


class GradientView: UIView {

    private let gradient : CAGradientLayer = CAGradientLayer()
    private let gradientStartColor: UIColor
    private let gradientEndColor: UIColor

    init(gradientStartColor: UIColor, gradientEndColor: UIColor) {
        self.gradientStartColor = gradientStartColor
        self.gradientEndColor = gradientEndColor
        super.init(frame: .zero)
    }

    required init?(coder aDecoder: NSCoder) { fatalError("init(coder:) has not been implemented") }

    override func layoutSublayers(of layer: CALayer) {
        super.layoutSublayers(of: layer)
        gradient.frame = self.bounds
    }

    override public func draw(_ rect: CGRect) {
        gradient.frame = self.bounds
        gradient.colors = [gradientEndColor.cgColor, gradientStartColor.cgColor]
        gradient.startPoint = CGPoint(x: 1, y: 0)
        gradient.endPoint = CGPoint(x: 0.2, y: 1)
        if gradient.superlayer == nil {
            layer.insertSublayer(gradient, at: 0)
        }
    }
}

创建 UIView 后，您只需向该视图添加约束。

Answer 4

受此处解决方案的启发，我创建了以下 class。

使用示例：

// Simple usage. From clear to black.
let gradientView1 = GradientView(colors: [.clear, .black])

// Tweak locations. Here the gradient from red to green will take 30% of the view.
let gradientView2 = GradientView(colors: [.red, .green, .blue], locations: [0, 0.3, 1])

// Create your own gradient.
let gradient = CAGradientLayer()
gradient.colors = [UIColor.red.cgColor, UIColor.blue.cgColor]
let gradientView3 = GradientView(gradient: gradient)

class:

import UIKit

/**
 * View with a gradient layer.
 */
class GradientView: UIView {

    let gradient : CAGradientLayer

    init(gradient: CAGradientLayer) {
        self.gradient = gradient
        super.init(frame: .zero)
        self.gradient.frame = self.bounds
        self.layer.insertSublayer(self.gradient, at: 0)
    }

    convenience init(colors: [UIColor], locations:[Float] = [0.0, 1.0]) {
        let gradient = CAGradientLayer()
        gradient.colors = colors.map { [=11=].cgColor }
        gradient.locations = locations.map { NSNumber(value: [=11=]) }
        self.init(gradient: gradient)
    }

    override func layoutSublayers(of layer: CALayer) {
        super.layoutSublayers(of: layer)
        self.gradient.frame = self.bounds
    }

    required init?(coder: NSCoder) { fatalError("no init(coder:)") }
}

使用自动布局为 UIView 应用渐变背景

Applying gradient background for UIView using auto layout

objective-c

uiview

ios

cagradientlayer

swift3