在Swift 3中通过Core Graphics绘制文本 [英] Drawing text over Core Graphics in Swift 3

问题描述

背景:我正在使用带有核心图形的UIImageView进行绘制.我最终希望在核心图形图形上绘制一个文本字符串.

Background: I am drawing on a UIImageView with Core Graphics. I would like to ultimately draw a text string over the core graphics drawing.

我曾经使用过这种(hackingwithswift.com)方法将文本绘制到图像上，将imageView设置为该图像，然后使用核心图形进行绘制.但我希望文本覆盖核心图形.

This (hackingwithswift.com) method i used to draw the text to an image, set my imageView to that image, and then draw over with core graphics. But I want the text to overlay the core graphics drawing.

现在，我已移至此 https://stackoverflow.com/a/35574171/6337391 ，但它仍然不是允许我在图纸上写字.

Now I have moved to this https://stackoverflow.com/a/35574171/6337391 but it still isnt allowing me to write on top of my drawing.

class MapViewController: UIViewController {

    @IBOutlet var imageView: UIImageView!

    func drawScale() {
        // establish 6 points to draw a little bar with
        let length = CGFloat(80.0)
        let bottom = imageView.bounds.size.height - 15.0
        let left = CGFloat(20.0)
        let top = bottom - 20.0
        let middle = top + 10.0
        let right = left + length
        let topLeft = CGPoint(x: left, y: top)
        let topRight = CGPoint(x: right, y: top)
        let bottomRight = CGPoint(x: right, y: bottom)
        let bottomLeft = CGPoint(x: left, y: bottom)
        let middleLeft = CGPoint(x: left, y: middle)
        let middleRight = CGPoint(x: right, y: middle)

        // draw the bar
        drawLineFrom(fromPoint: topLeft, toPoint: bottomLeft, color: UIColor.red.cgColor, width: 1.0, alias: false)
        drawLineFrom(fromPoint: topRight, toPoint: bottomRight, color: UIColor.red.cgColor, width: 1.0, alias: false)
        drawLineFrom(fromPoint: middleLeft, toPoint: middleRight, color: UIColor.red.cgColor, width: 1.0, alias: false)

        // draw a text string
        UIGraphicsBeginImageContext(self.imageView.frame.size)

        let paragraphStyle = NSMutableParagraphStyle()
        paragraphStyle.alignment = .center

        let attrs = [
            NSFontAttributeName: UIFont.systemFont(ofSize: 12),
            NSParagraphStyleAttributeName: paragraphStyle,
            NSForegroundColorAttributeName: UIColor.red]

        let scaleString = "45 feet"
        scaleString.draw(at: CGPoint(x: 0, y: 50), withAttributes: attrs)

        let newImage = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
    }

    /* Stroke a line between two CGPoints. Color, width, anti-alias options. */
    func drawLineFrom(fromPoint: CGPoint, toPoint: CGPoint, color: CGColor, width: CGFloat, alias: Bool) {
        // 1
        UIGraphicsBeginImageContext(self.imageView.frame.size)
        let context = UIGraphicsGetCurrentContext()!
        context.setShouldAntialias(alias)
        self.imageView.image?.draw(in: CGRect(x: 0, y: 0, width: self.imageView.frame.size.width, height: self.imageView.frame.size.height))

        // 2
        context.move(to: fromPoint)
        context.addLine(to: toPoint)

        // 3
        context.setLineWidth(width)
        context.setStrokeColor(color)

        // 4
        context.strokePath()

        // 5
        self.imageView.image = UIGraphicsGetImageFromCurrentImageContext()
        self.imageView.alpha = 1.0
        UIGraphicsEndImageContext()
    }
}

不工作.绘制文本字符串将完全擦除该条.如果将条形图代码移到字符串形图代码下，则两者都可见，但是条形图当然在字符串上.

Doesnt work. Drawing the text string completely erases the bar. If move the bar drawing code under the string drawing code, then both are visible, but of course the bar is then over the string.

推荐答案

使用Swift 4:

let paragraphStyle = NSMutableParagraphStyle()
paragraphStyle.alignment = .center

let attributes = [
    NSAttributedStringKey.paragraphStyle: paragraphStyle,
    NSAttributedStringKey.font: UIFont.systemFont(ofSize: 12.0),
    NSAttributedStringKey.foregroundColor: UIColor.blue
]

let myText = "HELLO"
let attributedString = NSAttributedString(string: myText, attributes: attributes)

let stringRect = CGRect(x: W/2 - 50, y: border, width: 100, height: H)
attributedString.draw(in: stringRect)

对于Swift 4.2，将上面的attributes更改为:

For Swift 4.2, change the above attributes to:

let attributes: [NSAttributedString.Key : Any] = [
    .paragraphStyle: paragraphStyle,
    .font: UIFont.systemFont(ofSize: 12.0),
    .foregroundColor: UIColor.blue
]

这篇关于在Swift 3中通过Core Graphics绘制文本的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！