在Swift 3中，如何在Core Graphics上绘制文本？

Question

在Swift 3中，如何在Core Graphics上绘制文本？

18

背景：我正在使用核心图形在UIImageView上绘制。我最终想在核心图形绘制的上面绘制文本字符串。这个(hackingwithswift.com)方法是我用来将文本绘制到图像上，将我的imageView设置为该图像，然后用核心图形进行绘制。但是我希望文本覆盖核心图形绘制。

现在我已经转向了https://dev59.com/XmEi5IYBdhLWcg3wd8EF#35574171，但它仍然不允许我在我的绘图上面写字。

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()
    }
}

无法正常工作。绘制文本字符串会完全擦除该条。如果将该条绘制代码移至字符串绘制代码下方，则两者均可见，但当然该条会覆盖字符串。

- Harry Netzer

你能否将文本创建为CATextLayer并添加到图像视图中？ - user7014451

你所说的“我正在使用核心图形在UIImageView上绘图”，是什么意思？你的代码运行在哪个类下面？ - El Tomato

我添加了一些上下文代码，希望能有所帮助。我认为答案可能在Core Text中，我将尝试自己找到解决方案。像链接这样的东西看起来很有前途。 - Harry Netzer

2个回答

4

Swift 3.0：绘制文本

   func drawMyText(myText:String,textColor:UIColor, FontName:String, FontSize:CGFloat, inRect:CGRect){

     let textFont = UIFont(name: FontName, size: FontSize)!
    let textFontAttributes = [
        NSFontAttributeName: textFont,
        NSForegroundColorAttributeName: textColor,
        ] as [String : Any]

    myText.draw(in: inRect, withAttributes: textFontAttributes)
}

调用这个函数，下面是一个例子。

let _rect = CGRect(x: 40, y: 100, width: 40, height: 40)

 drawMyText(myText: "Hello", textColor: UIColor.black, FontName: "Helvetica Bold", FontSize: 11 , inRect:_rect)

- Devesh.452

那只是在您的代码中删除了 UIGraphicsBeginImageContext(self.imageView.frame.size)。您的代码在我的情况下没有绘制任何文本。 - Harry Netzer

将drawMyText函数放在UIView子类中，并从drawRect函数中调用它，如果需要进一步帮助，请告诉我。 - Devesh.452

1

我的问题是绘制文本会擦除之前绘制的内容。在我上面的示例中，文本将出现，但它完全擦除了我之前绘制的线条。据我所知，您只建议我在矩形中绘制文本而不是在点上，这对我没有任何帮助。 - Harry Netzer

小文本。我想将文本绘制为图像大小。 - shinriyo

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- ingconti · Accepted Answer

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，将上述attributes更改为：

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