ios - 自定义 UIView 中的无效上下文 0x0 - 后续问题

Question

这篇文章: invalid context 0x0 within custom UIView...应该给我解决问题的关键，但我无法避免无效上下文错误。一些澄清将不胜感激。

我想在 ViewController 加载时显示的 subview 中画线。为此，我为 UIView 创建了一个子类，它类似于 StartPlayer 发布的 SplitCircleView。

要运行代码，请创建一个新项目并将 ViewController 文件的内容替换为:

import UIKit
@IBDesignable

class ViewController: UIViewController {
    let mySubViewInstance = SplitCircleView()

    override func viewDidLoad() {
        super.viewDidLoad()

        //let mySubViewInstance = SplitCircleView()
        mySubViewInstance.setNeedsDisplay(mySubViewInstance.frame)
    }
}

class SplitCircleView: UIView {
    override init(frame: CGRect) {
        super.init(frame: frame)
        //self.setNeedsDisplay()
        //draw(frame)
    }

    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        //self.setNeedsDisplay()
        //draw(frame)
    }

    override func setNeedsDisplay(_ rect: CGRect) {
        self.backgroundColor = .clear

        drawSlice(rect: rect, startPercent: 87.5, endPercent: 37.5, color: .green)
        drawSlice(rect: rect, startPercent: 37.5, endPercent: 87.5, color: .red)
    }

    func drawSlice(rect: CGRect, startPercent: CGFloat, endPercent: CGFloat, color: UIColor) {
        let center = CGPoint(x: rect.origin.x + rect.width / 2, y: rect.origin.y + rect.height / 2)
        let radius = (min(rect.width, rect.height) / 2)
        let startAngle = startPercent / 100 * .pi * 2 - .pi
        let endAngle = endPercent / 100 * .pi * 2 - .pi
        let path = UIBezierPath()

        path.move(to: center)
        path.addArc(withCenter: center, radius: radius, startAngle: startAngle, endAngle: endAngle, clockwise: true)
        path.close()
        color.setFill()
        path.fill()
    }
}

如何避免无效上下文错误并在加载 ViewController 时在 subview 中绘制内容？

Answer 1

您应该覆盖 draw，而不是 setNeedsDisplay。

override func draw(_ rect: CGRect) {
    self.backgroundColor = .clear

    drawSlice(rect: rect, startPercent: 87.5, endPercent: 37.5, color: .green)
    drawSlice(rect: rect, startPercent: 37.5, endPercent: 87.5, color: .red)
}

背景颜色的设置只需要设置一次，所以 draw 并不是该行的理想位置。将其移动到 init。

setNeedsDisplay 表示绘图需要更新。但实际绘制的是 draw。