PHAsset：使用元数据保存新图像

Question

我正在使用 UIImagePickerController 来允许用户使用相机拍照。当代理被调用时，我想将图像保存到照片库/相机胶卷中，这是使用 PHAssetChangeRequest 执行的。问题是文档说我可以使用 UIImagePickerControllerMediaMetadata 中的字典将其作为元数据包含在内，但 PHAssetChangeRequest 似乎没有参数来执行此操作。保存时如何包含此元数据？谢谢！

Answer 1

您可以使用

PHAssetCreationRequest

。为了使用

PHAssetCreationRequest

，您将合并imageData和元数据，然后将imageDataWithMetadata写入相册。像这样：

if let imageDataWithMetadata = self.writeMetadata(metadata, into: imageData) {
    self.saveImageDataForiOS9(imageDataWithMetadata)
}

func saveImageDataForiOS9(_ data: Data) {
    var newImageIdentifier: String!

    PHPhotoLibrary.shared().performChanges({
        if #available(iOS 9.0, *) {
            let assetRequest = PHAssetCreationRequest.forAsset()
            assetRequest.addResource(with: .photo, data: data, options: nil)
            newImageIdentifier = assetRequest.placeholderForCreatedAsset!.localIdentifier
        } else {
            // Fallback on earlier versions
        }
    }) { (success, error) in
        DispatchQueue.main.async(execute: {
            if success, let newAsset = PHAsset.fetchAssets(withLocalIdentifiers: [newImageIdentifi
                // ...
            } else {
                // ...
            }
        })

    }
}

对于 iOS 8，您可以使用

ALAssetsLibrary

保存带有元数据的新图像：

func saveImageDataForiOS8(_ imageData: Data, _ metadata: Dictionary<AnyHashable, Any>?) {
    let library = ALAssetsLibrary()
    library.writeImageData(toSavedPhotosAlbum: imageData, metadata: metadata, completionBlock: { (newURL, error) in
        if let _ = error {
            // ...
        } else {
            if let newAsset = PHAsset.fetchAssets(withALAssetURLs: [newURL!], options: nil).firstObject {
                // ...
            }
        }
    })
}

所以，最终你将得到这样的代码：

func saveImage(_ imageData: Data, metadata: Dictionary<AnyHashable, Any>?) {
    if #available(iOS 9.0, *) {
        if let metadata = metadata {
            if let imageDataWithMetadata = self.writeMetadata(metadata, into: imageData) {
                self.saveImageDataForiOS9(imageDataWithMetadata)
            } else {
                self.saveImageDataForiOS9(imageData)
            }
        } else {
            self.saveImageDataForiOS9(imageData)
        }
    } else {
        self.saveImageDataForiOS8(imageData, metadata)
    }
}

func saveImageDataForiOS8(_ imageData: Data, _ metadata: Dictionary<AnyHashable, Any>?) {
    let library = ALAssetsLibrary()
    library.writeImageData(toSavedPhotosAlbum: imageData, metadata: metadata, completionBloc
        if let _ = error {
            // ...
        } else {
            if let newAsset = PHAsset.fetchAssets(withALAssetURLs: [newURL!], options: nil).
                // ...
            }
        }
    })
}

func saveImageDataForiOS9(_ data: Data) {
    var newImageIdentifier: String!

    PHPhotoLibrary.shared().performChanges({
        if #available(iOS 9.0, *) {
            let assetRequest = PHAssetCreationRequest.forAsset()
            assetRequest.addResource(with: .photo, data: data, options: nil)
            newImageIdentifier = assetRequest.placeholderForCreatedAsset!.localIdentifier
        } else {
            // Fallback on earlier versions
        }
    }) { (success, error) in
        DispatchQueue.main.async(execute: {
            if success, let newAsset = PHAsset.fetchAssets(withLocalIdentifiers: [newImageId
                // ...
            } else {
                // ...
            }
        })

    }
}

internal func writeMetadata(_ metadata: Dictionary<AnyHashable, Any>, into imageData: Data) 
    let source = CGImageSourceCreateWithData(imageData as CFData, nil)!
    let UTI = CGImageSourceGetType(source)!

    let newImageData = NSMutableData()
    if let destination = CGImageDestinationCreateWithData(newImageData, UTI, 1, nil) {
        CGImageDestinationAddImageFromSource(destination, source, 0, metadata as CFDictionar
        if CGImageDestinationFinalize(destination) {
            return newImageData as Data
        } else {
            return nil
        }
    } else {
        return nil
    }
}

Answer 2

据我通过阅读源代码了解到，Apple 所说的元数据是指资产的属性。

open var pixelWidth: Int { get }
open var pixelHeight: Int { get }
open var creationDate: Date? { get }
open var modificationDate: Date? { get }
open var location: CLLocation? { get }
open var duration: TimeInterval { get }
open var isHidden: Bool { get }

其他元数据可以通过访问 CGImage 属性在图像中找到。

Answer 3

在

UIImagePickerControllerDelegate

中读出元数据和图像，如下所示：

func imagePickerController(_ picker: UIImagePickerController, didFinishPickingMediaWithInfo info: [UIImagePickerController.InfoKey : Any]) {
    let metadata = info[UIImagePickerController.InfoKey.mediaMetadata] as? [CFString: Any]
    let image = info[UIImagePickerController.InfoKey.originalImage] as? UIImage

    // start processing image below

}

然后将带有元数据的图像保存到临时 URL。例如如下：

extension UIImage {

func saveAsHEIC(fileURL: URL, compressionQuality: CGFloat, metadata: [CFString: Any]?) -> Bool {
        guard let cgImage = cgImage else { return false }
        guard let destination = CGImageDestinationCreateWithURL(fileURL as CFURL, "public.heic" as CFString, 1, nil) else { return false }
        
        var dict = metadata ?? [CFString: Any]()
        dict[kCGImageDestinationLossyCompressionQuality] = compressionQuality
        dict[kCGImagePropertyOrientation] = cgImageOrientation.rawValue
        
        CGImageDestinationAddImage(destination, cgImage, dict as CFDictionary)
        return CGImageDestinationFinalize(destination)
    }
}

然后将保存在临时文件中的图像插入照片库，如下所示：

PHPhotoLibrary.shared().performChanges( 
{ 
   PHAssetChangeRequest.creationRequestForAssetFromImage(atFileURL: url)
},
  completionHandler: { 
   // ...
})

如果您想将位置数据包含到图像中，则必须使用 CoreLocation 请求位置访问，并根据规范手动填充元数据中的密钥

kCGImagePropertyGPSDictionary

。