ios - 获取 UIBezierPath 的起点

Question

我创建了一个 UIBezierPath，但我不知道如何访问它的起点。我试过这样做:

let startPoint = path.currentPoint

属性 currentPoint 给我最后一点，而不是起点。我需要起点的原因是因为我想在路径的起点放置一个图像。

有什么想法吗？

Answer 1

您需要下拉到 CGPath 并使用 CGPathApply 遍历元素。您只想要第一个，但您必须查看所有。

我假设您的路径格式正确，并且以“移动”开头。这对于 UIBezierPath 应该总是正确的(我不知道有什么方法可以让它不正确。)

您需要 rob mayoff 的 CGPath.forEach 的帮助，这很棘手，但有了它就很简单了:

// rob mayoff's CGPath.foreach
extension CGPath {
    func forEach(@noescape body: @convention(block) (CGPathElement) -> Void) {
        typealias Body = @convention(block) (CGPathElement) -> Void
        func callback(info: UnsafeMutablePointer<Void>, element: UnsafePointer<CGPathElement>) {
            let body = unsafeBitCast(info, Body.self)
            body(element.memory)
        }
        let unsafeBody = unsafeBitCast(body, UnsafeMutablePointer<Void>.self)
        CGPathApply(self, unsafeBody, callback)
    }
}

// Finds the first point in a path
extension UIBezierPath {
    func firstPoint() -> CGPoint? {
        var firstPoint: CGPoint? = nil

        self.CGPath.forEach { element in
            // Just want the first one, but we have to look at everything
            guard firstPoint == nil else { return }
            assert(element.type == .MoveToPoint, "Expected the first point to be a move")
            firstPoint = element.points.memory
        }
        return firstPoint
    }
}

---

在 Swift 3 中，基本相同:

// rob mayoff's CGPath.foreach
extension CGPath {
    func forEach( body: @convention(block) (CGPathElement) -> Void) {
        typealias Body = @convention(block) (CGPathElement) -> Void
        func callback(info: UnsafeMutableRawPointer?, element: UnsafePointer<CGPathElement>) {
            let body = unsafeBitCast(info, to: Body.self)
            body(element.pointee)
        }
        let unsafeBody = unsafeBitCast(body, to: UnsafeMutableRawPointer.self)
        self.apply(info: unsafeBody, function: callback)
    }
}

// Finds the first point in a path
extension UIBezierPath {
    func firstPoint() -> CGPoint? {
        var firstPoint: CGPoint? = nil

        self.cgPath.forEach { element in
            // Just want the first one, but we have to look at everything
            guard firstPoint == nil else { return }
            assert(element.type == .moveToPoint, "Expected the first point to be a move")
            firstPoint = element.points.pointee
        }
        return firstPoint
    }
}