你是如何从Unmanaged<CGColorSpace>获得CGColorSpace的？

Question

我正在用Swift编写一个函数，它从一个vImage_CGImageFormat创建一个CGImage，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。这是因为CGImageGetColorSpace(image)返回CGColorSpace!，上面的构造函数只将Unmanaged<CGColorSpace>作为colorSpace参数。

还有别的办法吗？也许将CGColorSpace转换为Unmanaged<CGColorSpace>

Answer 1

这应该是可行的：

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>

Swift 3的更新：

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