ios - 在物体后面获得色彩

我想反转一个如下所示的按钮:



在这种情况下，反转意味着将标题设置为蓝色，将按钮的背景设置为白色。由于我不想对其进行硬编码，因此不能简单地将其设置为蓝色。当然，当我将背景色设置为白色，而标题的颜色设置为clearColor时，标题不再可读:



有没有办法找出按钮后面的颜色(当前是视图的背景图像)，因此我可以将标题的颜色设置为该颜色？
提前致谢 :)

最佳答案

在Kjuly's answer之后，您应该创建一个UIButton子类来执行此操作。

为了应用您的不同样式，您只想为按钮触摸事件添加一些动作侦听器，以便在状态更改时重新绘制按钮。

如Kjuly所说，然后您将要覆盖drawRect，以便根据是否按下按钮来绘制自定义按钮。

这样的事情应该可以实现您的追求。

class CustomButton: UIButton {

    private let paragraphStyle = NSMutableParagraphStyle()
    private var titleAttributes = [String:AnyObject]()
    private var isPressed = false

    var highlightColor = UIColor.whiteColor() { // stroke & highlight color of the button
        didSet {
            setNeedsDisplay()
        }
    }
    var cornerRadius:CGFloat = 10.0 { // corner radius of button
        didSet {
            setNeedsDisplay()
        }
    }
    var strokeWidth:CGFloat = 5.0 { // stroke width of button
        didSet {
            setNeedsDisplay()
        }
    }
    override init(frame: CGRect) {
        super.init(frame: frame)

        addTarget(self, action: Selector("buttonWasPressed"), forControlEvents: .TouchDown)
        addTarget(self, action: Selector("buttonWasReleased"), forControlEvents: .TouchUpInside)
        addTarget(self, action: Selector("buttonWasReleased"), forControlEvents: .TouchDragExit)
        addTarget(self, action: Selector("buttonWasReleased"), forControlEvents: .TouchCancel)
    }

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

    func buttonWasPressed() {
        isPressed = true
        setNeedsDisplay() // set button to be redrawn
    }

    func buttonWasReleased() {
        isPressed = false
        setNeedsDisplay() // set button to be redrawn
    }

    override func drawRect(rect: CGRect) {

        let size = bounds.size
        let context = UIGraphicsGetCurrentContext()

        if isPressed { // button pressed down

            let path = UIBezierPath(roundedRect: bounds, cornerRadius: cornerRadius) // path of button shape for filling

            CGContextSetFillColorWithColor(context, highlightColor.CGColor) // white background of the button
            path.fill() // fill path

            CGContextSetBlendMode(context, .DestinationOut) // set blend mode for transparent label

        } else { // button not pressed

            let path = UIBezierPath(roundedRect: UIEdgeInsetsInsetRect(bounds, UIEdgeInsets(top: strokeWidth*0.5, left: strokeWidth*0.5, bottom: strokeWidth*0.5, right: strokeWidth*0.5)), cornerRadius: cornerRadius-strokeWidth*0.5) // path of button shape for stroking

            CGContextSetStrokeColorWithColor(context, highlightColor.CGColor) // set stroke color
            path.lineWidth = strokeWidth
            path.stroke()
        }

        guard let label = titleLabel else {return} // title label
        guard let text = label.text else {return} // text to draw

        // update text attributes, add any extra attributes you want transferred here.
        paragraphStyle.alignment = label.textAlignment
        titleAttributes[NSFontAttributeName] = label.font
        titleAttributes[NSParagraphStyleAttributeName] = paragraphStyle
        titleAttributes[NSForegroundColorAttributeName] = label.textColor

        let textHeight = text.sizeWithAttributes(titleAttributes).height // heigh of the text to render, with the attributes
        let renderRect = CGRect(x:0, y:(size.height-textHeight)*0.5, width:size.width, height:size.height) // rect to draw the text in

        text.drawInRect(renderRect, withAttributes: titleAttributes) // draw text
    }
}

然后，可以通过在按钮的titleLabel上设置各种属性以及strokeWidth和cornerRadius属性来使用此按钮。例如:

let button = CustomButton(frame: CGRect(x: 50, y: 50, width: 200, height: 75))

button.titleLabel?.text = "Let's go!"
button.titleLabel?.font = UIFont.systemFontOfSize(30)
button.titleLabel?.textAlignment = .Center
button.titleLabel?.textColor = UIColor.whiteColor()

button.cornerRadius = 15.0
button.strokeWidth = 5.0
view.addSubview(button)

关于ios - 在物体后面获得色彩，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/35377272/