ios - 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，我使用 PHAssetChangeRequest 执行此操作。问题是文档说我可以使用 UIImagePickerControllerMediaMetadata 中的字典将其包含为元数据，但 PHAssetChangeRequest 似乎没有执行此操作的参数。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元数据保存新图像：

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，最后你会得到这样的代码：

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

从我通过阅读源代码可以理解的情况来看，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 }

通过访问 CGImage 属性，可以在图像中找到其他元数据。