你如何从 CGColorSpace 获得 Unmanaged<CGColorSpace>？

Question

我正在 Swift 中编写一个函数，它从 CGImage 创建一个 vImage_CGImageFormat，如下所示：

vImage_CGImageFormat(
    bitsPerComponent: UInt32(CGImageGetBitsPerComponent(image)), 
    bitsPerPixel: UInt32(CGImageGetBitsPerPixel(image)), 
    colorSpace: CGImageGetColorSpace(image), 
    bitmapInfo: CGImageGetBitmapInfo(image), 
    version: UInt32(0), 
    decode: CGImageGetDecode(image), 
    renderingIntent: CGImageGetRenderingIntent(image))

然而这并不能编译。那是因为 CGImageGetColorSpace(image) returns CGColorSpace! 而上面的构造函数只需要 Unmanaged<CGColorSpace> 作为 colorSpace 参数。

还有其他方法吗？也许将 CGColorSpace 转换为 Unmanaged<CGColorSpace>?

Answer 1

这应该有效：

vImage_CGImageFormat(
    // ...
    colorSpace: Unmanaged.passUnretained(CGImageGetColorSpace(image)),
    //...
)

来自 struct Unmanaged<T> API 文档：

/// Create an unmanaged reference without performing an unbalanced
/// retain.
///
/// This is useful when passing a reference to an API which Swift
/// does not know the ownership rules for, but you know that the
/// API expects you to pass the object at +0.
///
/// ::
///
///   CFArraySetValueAtIndex(.passUnretained(array), i,
///                          .passUnretained(object))
static func passUnretained(value: T) -> Unmanaged<T>

Swift3 的更新：

vImage_CGImageFormat(
    // ...
    colorSpace: Unmanaged.passUnretained(image.colorSpace!),
    //...
)

你如何从 CGColorSpace 获得 Unmanaged<CGColorSpace>？

How do you get Unmanaged<CGColorSpace> from CGColorSpace?

core-graphics

ios

swift

vimage