通过图片的URL 获取Asset

 if let referenceURL = info[UIImagePickerControllerReferenceURL] as? URL {
        let options = PHFetchOptions()
        options.sortDescriptors = [NSSortDescriptor(key: "creationDate", ascending: false)]
        options.predicate = NSPredicate(format: "mediaType = %d OR mediaType = %d",PHAssetMediaType.image.rawValue, PHAssetMediaType.video.rawValue)
        let fetchResult = PHAsset.fetchAssets(withALAssetURLs: [referenceURL], options: options)
        if let asset = fetchResult.firstObject {
              return asset
        }
}