Nil 与预期的参数类型 CGAffineTransform 不兼容

Question

我正在尝试绘制路径：CGMutablePath 但我在添加路径时遇到问题。 Nil 与预期的参数类型不兼容 'UnsafePointer'CGAffineTransform'

override func draw(_ rect: CGRect) {

            let context = UIGraphicsGetCurrentContext()

            let path = CGMutablePath()
            CGPathAddArc(path, nil, centerX, centerY, radius, -CGFloat(M_PI/2), CGFloat(GLKMathDegreesToRadians(currentAngle)), false)

            context!.addPath(path)
            context!.setStrokeColor(UIColor.blue.cgColor)
            context!.setLineWidth(3)
            context!.strokePath()
       }

尝试了一些将 nil 替换为 0, options: nil, options: [ ] none 的方法。

在@vadian 回答的帮助下。解决方案：

override func draw(_ rect: CGRect) {

            let context = UIGraphicsGetCurrentContext()!

            let path = CGMutablePath()
            path.addArc(center: CGPoint(x:centerX, y:centerY), radius: radius, startAngle: -(CGFloat.pi / 2), endAngle: CGFloat(GLKMathDegreesToRadians(currentAngle)), clockwise: false)

            context.addPath(path)
            context.setStrokeColor(UIColor.blue.cgColor)
            context.setLineWidth(3)
            context.strokePath()
       }

Answer 1

CGMutablePath在Swift3中添加弧的函数签名为

func addArc(center: CGPoint, radius: CGFloat, startAngle: CGFloat, endAngle: CGFloat, clockwise: Bool, transform: CGAffineTransform = default)

在你的情况下（center 必须是 CGPoint）

path.addArc(center: CGPoint(x:centerX, y:centerY), 
            radius: radius, 
        startAngle: -(CGFloat.pi / 2), 
          endAngle: CGFloat(GLKMathDegreesToRadians(currentAngle)), 
         clockwise: false)

为了避免四个感叹号直接展开上下文

let context = UIGraphicsGetCurrentContext()!

并删除所有其他 !。

Nil 与预期的参数类型 CGAffineTransform 不兼容

Nil is not compatible with expected argument type CGAffineTransform

swift

swift3

cgaffinetransform

cgrect

cgpath