Swift NSImage到CGImage

Question

如何在Swift中将NSImage转换为CGImage？在Objective-C中，我这样做：

- (CGImageRef)CGImage {
    NSData *imageData = self.TIFFRepresentation;
    CGImageSourceRef source = CGImageSourceCreateWithData((__bridge CFDataRef)imageData, NULL);
    CGImageRef maskRef =  CGImageSourceCreateImageAtIndex(source, 0, NULL);
    return maskRef;
}

现在我尝试了：

extension NSImage {
    var CGImage: CGImageRef {
    get {
        let imageData = self.TIFFRepresentation
        let source = CGImageSourceCreateWithData(imageData as CFDataRef, nil)
        let maskRef = CGImageSourceCreateImageAtIndex(source, UInt(0), nil)
        return maskRef;
    }
    }
}

我无法编译，我收到错误：Could not find an overload for 'init' that accepts the supplied arguments'行let maskRef ...

Answer 1

这是我用来将NSImage转换为CGImage的方法：

let image = NSImage(named:"image")
if let image = image {
    var imageRect:CGRect = CGRectMake(0, 0, image.size.width, image.size.height)
    var imageRef = image.CGImageForProposedRect(&imageRect, context: nil, hints: nil)
}

Answer 2

啊，我找到了解决方案。这是因为在Swift中你只有一个非托管对象（我只是不明白，这意味着什么）。但是这个代码现在有效：

extension NSImage {
    var CGImage: CGImageRef {
    get {
        let imageData = self.TIFFRepresentation
        let source = CGImageSourceCreateWithData(imageData as CFDataRef, nil).takeUnretainedValue()
        let maskRef = CGImageSourceCreateImageAtIndex(source, UInt(0), nil)
        return maskRef.takeUnretainedValue();
    }
    }
}

Answer 3

Swift 3和4版本代码： -

if let image = NSImage(named: "Icon"){
    let cgImage = image.cgImage(forProposedRect: nil, context: nil, hints: nil)
}

Answer 4

对于Swift 4.0，XCode 9.2：

extension NSImage {
    @objc var CGImage: CGImage? {
       get {
            guard let imageData = self.tiffRepresentation else { return nil }
            guard let sourceData = CGImageSourceCreateWithData(imageData as CFData, nil) else { return nil }
            return CGImageSourceCreateImageAtIndex(sourceData, 0, nil)
       }
    }
}