Objective c Photokit中的元数据（EXIF、TIFF等）

在iOS 8中，使用新的PhotoKit，创建新映像的方法是使用

-[PHPhotoLibrary performChanges:completionHandler]

，方法如下：

[[PHPhotoLibrary sharedPhotoLibrary]性能更改：^{
PHAssetChangeRequest*changeRequest=[PHAssetChangeRequest creationRequestForAssetFromImage:image]；
//如何设置元数据？
}completionHandler:^（布尔成功，N错误*错误）{
如果（成功）
{
//做事
}
}];

但是，我找不到任何关于如何在图像上设置元数据的文档

在旧的ALAssetLibrary中（它仍然有效，并且可能仍然是前进的“正确”方式），您只需使用

-[ALAssetLibrary WritePhotosSavedPhotosAlbum:metadata:completionBlock:

，它允许您传入元数据字典

---

PhotoKit中是否有等效的方法？

使用临时文件可以获得相同的结果。例如：

import Photos
import ImageIO
import MobileCoreServices

PHPhotoLibrary.sharedPhotoLibrary().performChanges ({
    let temporaryPath = ... // a path in the App's documents or cache directory
    let fileURL = NSURL.fileURLWithPath (temporaryPath)!

    // custom UIImagePNGRepresentation function is implemented below
    let PNGdataWithMetadata = UIImagePNGRepresentation (photo, copyright: "Image Copyright",
                author: "Image Author", description: "Image Description")
    let createAssetRequest = PHAssetChangeRequest.creationRequestForAssetFromImageAtFileURL (fileURL)
}, completionHandler: { (success, error) in
       // to-do: delete the temporary file            
        println ("completion \(success) \(error)")
})

---

---

我正在复制项目中的粘贴代码，希望我没有遗漏任何内容。

您遗漏了实际将数据保存到fileURL的代码；）还请注意，相机应用程序将它们保存为JPG而不是PNG。保存为PNG为我生成了一个4.5 MB的文件，而使用相机拍摄时只有850 KB。这将创建新图像。您知道如何编辑现有照片资源图像的元数据吗？

// what the custom UIImagePNGRepresentation function does is create a PNG representation that contains the given metadata. The function assumes all functions return valid data
// to add the metadata to the PNG representation of the image we:
// 1. create the PNG representation and read the default values (these will include things like the image's size)
// 2. add the metadata items (see CGImageProperties Reference for the valid keys)
// 3. create an image destination where the new PNG will be created and assigned the metadata dictionary 

public func UIImagePNGRepresentation (image : UIImage, # copyright : String, # author : String, # description : String) -> NSData {
    // wrap the valid metadata values in a dictionary
    var PNGmetadata = [String : AnyObject] ()
    PNGmetadata [kCGImagePropertyPNGCopyright] = copyright
    PNGmetadata [kCGImagePropertyPNGAuthor] = author
    PNGmetadata [kCGImagePropertyPNGDescription] = description

    let metadata = [kCGImagePropertyPNGDictionary as String : PNGmetadata]
    return UIImagePNGRepresentation (image, metadata: metadata)
}

public func UIImagePNGRepresentation (image : UIImage, # metadata : [String : [String : AnyObject]]) -> NSData {
    let imageSource = CGImageSourceCreateWithData (UIImagePNGRepresentation (image), nil)
    let defaultAttributes = CGImageSourceCopyPropertiesAtIndex (imageSource, 0, nil) as NSDictionary
    let extendedAttributes = defaultAttributes.mutableCopy () as NSMutableDictionary

    for item in metadata {
        extendedAttributes [item.0] = item.1
    }

    var outputPNGdata = NSMutableData ()
    let imageDestination = CGImageDestinationCreateWithData (outputPNGdata, kUTTypePNG, 1, nil)
    CGImageDestinationAddImageFromSource (imageDestination, imageSource, 0, extendedAttributes)
    let success = CGImageDestinationFinalize (imageDestination)
    assert (success, "Fail!")

    return outputPNGdata
}