How to port Swift code with unmanaged references to Objective-C - objective-c

Question

I was trying to port the following Swift code to Objective-C:
var contextImage: UIImage? = ...
let image: CGImage? = contextImage?.cgImage
let dataProvider: CGDataProvider? = image?.dataProvider
let data: CFData? = dataProvider?.data
let baseAddress = CFDataGetBytePtr(data!)
contextImage = nil
let unmanagedData = Unmanaged<CFData>.passRetained(data!)
var pixelBuffer: CVPixelBuffer?
let status = CVPixelBufferCreateWithBytes(nil,
(image?.width)!,
(image?.height)!,
kCVPixelFormatType_32BGRA,
UnsafeMutableRawPointer( mutating: baseAddress!),
(image?.bytesPerRow)!,
{ releaseContext, baseAddress in
let contextData = Unmanaged<CFData>.fromOpaque(releaseContext!)
contextData.release()
},
unmanagedData.toOpaque(),
nil,
&pixelBuffer)
but I got stuck at the Unmanaged section and was not able to find the proper Objective-C way of doing that under ARC (the documentation of Unmanaged seems to exist only for Swift):
CGImageRef image = contextImage.CGImage;
CGDataProviderRef dataProvider = CGImageGetDataProvider(image);
CFDataRef data = CGDataProviderCopyData(dataProvider);
const UInt8 * baseAddress = CFDataGetBytePtr(data);
contextImage = nil;
// ... now what?
Eventually I accomplished it by integrating a Swift file into the Objective-C project but I still wonder, what is the proper way of porting that original Swift code in Objective-C?

Answer 1

I don't think you need Unmanaged. Even in the Swift documentation for this function RawPointers are used.
This is how the documentation looks like for the ObjC.
CVReturn CVPixelBufferCreateWithBytes (CFAllocatorRef allocator,
size_t width,
size_t height,
OSType pixelFormatType,
void *baseAddress,
size_t bytesPerRow,
CVPixelBufferReleaseBytesCallback releaseCallback,
void *releaseRefCon,
CFDictionaryRef pixelBufferAttributes,
CVPixelBufferRef *pixelBufferOut);
Its implementation could look something like this.
CVPixelBufferRef pixelBuffer = NULL;
cvErr = CVPixelBufferCreateWithBytes(kCFAllocatorDefault,
FRAME_WIDTH,
FRAME_HEIGHT,
kCVPixelFormatType_32BGRA,
(void*)CFDataGetBytePtr(imageData),
CGImageGetBytesPerRow(image),
NULL,
NULL,
NULL,
&pixelBuffer);
More in documentation for CVPixelBufferCreate.