swift - 如何使用隐式解包选项？

Question

我正在将 NSView 移植到 Swift，我需要使用 Quartz CGContextAddPath。

import Cocoa

class MYView: NSView {

    init(frame: NSRect) {
        super.init(frame: frame)
    }

    override func drawRect(dirtyRect: NSRect) {
        super.drawRect(dirtyRect)


        NSColor .redColor() .set()
        NSRectFill(self.bounds)
        var p :CGMutablePathRef = CGPathCreateMutable()
        var ctx =  NSGraphicsContext.currentContext().graphicsPort()
        CGContextAddPath(ctx, p) // compiler rejects this line

    }

}

您如何理解此错误消息？

Cannot convert the expression's type 'Void' to type 'CGContext!'

CGContextAddPath 的 Swift 签名是:

func CGContextAddPath(context: CGContext!, path: CGPath!)

我的错误是什么？

当我使用它时:

let context = UnsafePointer<CGContext>(ctx).memory

我现在有一个运行时错误:

Jun 3 15:57:13 xxx.x SwiftTest[57092] <Error>: CGContextAddPath: invalid context 0x7fff73bd0060. This is a serious error. This application, or a library it uses, is using an invalid context and is thereby contributing to an overall degradation of system stability and reliability. This notice is a courtesy: please fix this problem. It will become a fatal error in an upcoming update.

这是我目前使用的代码:

import Cocoa

class MYView: NSView {

    init(frame: NSRect) {
        super.init(frame: frame)
    }

    override func drawRect(dirtyRect: NSRect) {
        super.drawRect(dirtyRect)

        var p :CGMutablePathRef =  CGPathCreateMutableCopy( CGPathCreateWithRoundedRect(self.bounds, 10, 10, nil))
        var ctx =  NSGraphicsContext.currentContext().graphicsPort()
        let context = UnsafePointer<CGContext>(ctx).memory

        CGContextAddPath(context, p) // compiler no longer rejects this line
        var blueColor = NSColor.blueColor()
        CGContextSetStrokeColorWithColor(context, NSColor.blueColor().CGColor)
        CGContextSetLineWidth(context, 2)
        CGContextStrokePath(context)

    }

}

Answer 1

从 Swift 1.0 开始

如果您的部署目标是 10.10，您可以使用优胜美地引入的便捷方法。

let context = NSGraphicsContext.currentContext().CGContext

如果您必须支持 10.9，则必须按照以下方式手动转换上下文。

let contextPtr = NSGraphicsContext.currentContext().graphicsPort
let context = unsafeBitCast(contextPtr, CGContext.self)