如何在swift中将COpaquePointer转换为某种类型(特别是CGContext？)

Question

我在swift中有以下代码,不能编译:

class CustomView: NSView {
  override func drawRect(dirtyRect: NSRect) {
    var contextPointer: COpaquePointer = NSGraphicsContext.currentContext()!.graphicsPort()
    var context: CGContext? = contextPointer as? CGContext
    CGContextSetRGBFillColor(context, 1, 0, 0, 1)
    CGContextFillRect(context, CGRectMake(0, 0, 100, 100))
    CGContextFlush(context)
  }
}

如何将COpaquePointer转换为CGContext？

Answer 1

截至开发者预览版5,NSGraphicsContext现在有一个CGContext属性.它还没有记录,但它在头文件中:

@property (readonly) CGContextRef CGContext NS_RETURNS_INNER_POINTER NS_AVAILABLE_MAC(10_10);

Answer 2

这有点难看; 如果更新了graphicsPort()方法以直接返回CGContextRef(例如UIGraphicsGetCurrentContext()),而不是void*,那会更好.我添加了这个扩展名,NSGraphicsContext以便现在将它扫到地毯下:

extension NSGraphicsContext {
  var cgcontext: CGContext {
    return Unmanaged<CGContext>.fromOpaque(self.graphicsPort()).takeUnretainedValue()
  }
}

只需NSGraphicsContext.currentContext().cgcontext在任何需要CGContext的地方打电话.

Answer 3

这似乎正在编译：

var contextPointer = NSGraphicsContext.currentContext()!.graphicsPort()
let context = UnsafePointer<CGContext>(contextPointer).memory