如何在饼图上为标签找到合适的位置？

Question

我没有使用任何库，所以这不是 this 的副本。

我自己画饼图是这样的：

var sections: [PieChartSection] = [] {
    didSet {
        setNeedsDisplay()
    }
}

override func draw(_ rect: CGRect) {
    let sumOfSections = sections.map { [=10=].value }.reduce(0, +)
    var pathStart = CGFloat.pi
    let smallerDimension = min(height, width)
    for section in sections {
        // draw section
        let percentage = section.value / sumOfSections
        let pathEnd = pathStart + CGFloat.pi * percentage.f * 2
        let path = UIBezierPath(arcCenter: CGPoint(x: bounds.midX, y: bounds.midY),
                                radius: smallerDimension / 4, startAngle: pathStart, endAngle: pathEnd, clockwise: true)

        //draw labels
        // this is my attempt at calculating the position of the labels
        let midAngle = (pathStart + pathEnd) / 2
        let textX = bounds.midX + smallerDimension * 3 / 8 * cos(midAngle)
        let textY = bounds.midY + smallerDimension * 3 / 8 * sin(midAngle)

        // creating the text to be shown, don't this is relevant
        let attributedString = NSMutableAttributedString(string: section.name, attributes: [
            .foregroundColor: UIColor.black.withAlphaComponent(0.15),
            .font: UIFont.systemFont(ofSize: 9)
            ])
        let formatter = NumberFormatter()
        formatter.maximumFractionDigits = 0
        let percentageString = "\n" + formatter.string(from: (percentage * 100) as NSNumber)! + "%"
        attributedString.append(NSAttributedString(string: percentageString, attributes: [
            .foregroundColor: UIColor.black.withAlphaComponent(0.5),
            .font: UIFont.systemFont(ofSize: 12)
            ]))
        attributedString.draw(at: CGPoint(x: textX, y: textY))

        // stroke path
        path.lineWidth = 6
        section.color.setStroke()
        path.stroke()
        pathStart = pathEnd
    }
}

PieChartSection 是一个简单的结构：

struct PieChartSection {
    let value: Double
    let color: UIColor
    let name: String
}

饼看起来不错，但标签有时离饼很远有时离饼很近：

我认为问题是 NSAttriutedString.draw 总是从左上角绘制文本，这意味着文本的 左上角 都是等距离的到饼图，而我需要绘制文本，以便它们 离饼图最近的点 都与饼图等距。

如何绘制这样的文字？

我没有使用 cocoa pod，因为我发现使用高级 API 很难按照我想要的方式制作图表。涉及的复杂性太多了。我希望对饼图的绘制方式进行较低级别的控制。

Answer 1

I think the problem is that NSAttriutedString.draw always draws the text from the top left corner

当然，draw 方法会将字符串的原点放在您经过的点上。在这种情况下，解决方案很简单 - 找到字符串的 size 并做出正确的来源。

let size = attributedString.size()
let origin = CGPoint(x: textX - size.width / 2, y: textY - size.height / 2)
attributedString.draw(at: origin)

结果：

如何在饼图上为标签找到合适的位置？

How do I find an appropriate position for my labels on a pie chart?

charts

drawing

ios

swift