从 photoLibrary 获取图像的元数据

Question

I need to get the metaData from an Image I'm picking via UIImagePickerController. This is my code:

func imagePickerController(_ picker: UIImagePickerController, didFinishPickingMediaWithInfo info: [UIImagePickerController.InfoKey : Any]) {
        let image = info[UIImagePickerController.InfoKey.originalImage] as! UIImage
        let metaData = info[UIImagePickerController.InfoKey.mediaMetadata] as? [AnyHashable: Any]
        print(metaData)
        picker.dismiss(animated: true, completion: nil)
    }

It works fine, when im picking the Image having.camera as source. But when I use.photoLibrary as source, then metaData is nil. I already read through other questions and tried stuff like

 let asset = info[.phAsset] as? PHAsset
 print(asset?.creationDate ?? "None")
 print(asset?.location ?? "None")

But this also returns nil. I guess the source of the problem is, that the info-Dictionary only returns 4 Keys when picking from.photoLibrary:

UIImagePickerControllerOriginalImage
UIImagePickerControllerMediaType
UIImagePickerControllerImageURL
UIImagePickerControllerReferenceURL

It would be awesome if someone could tell me where my mistake is. Thanks in advance !

Answer 1

I had the same problem. If the user does not grant access to the photo library first, info[.phAsset] will return nil.

Quote from Apple: "Accessing the photo library always requires explicit permission from the user. The first time your app uses PHAsset, PHCollection, PHAssetCollection, or PHCollectionList methods to fetch content from the library..."

Thus, you have to call PHPhotoLibrary.requestAuthorization{... } before presenting the image picker.

If the user denies the request, info[.phAsset] will also be nil!

Answer 2

This key is valid only when using an image picker whose source type is set to UIImagePickerController.SourceType.camera , and applies only to still images. The value for this key is an NSDictionary object that contains the metadata of the photo that was just captured. To store the metadata along with the image in the Camera Roll, use the PHAssetChangeRequest class from the Photos framework. https://developer.apple.com/documentation/uikit/uiimagepickercontroller/infokey/1619147-mediametadata