swift3.0 保存图片到本地，申请权限

<key>NSCameraUsageDescription</key>
<string>需要您的同意才能读取媒体资料库</string>
<key>NSLocationWhenInUseUsageDescription</key>
<string>需要您的同意才能读取媒体资料库</string>
<key>NSPhotoLibraryUsageDescription</key>
<string>需要您的同意才能读取媒体资料库</string>
<key>Privacy - Photo Library Usage Description</key>
<string>需要您的同意才能读取媒体资料库</string>

import Photos

//操作结果枚举
enum PhotoAlbumUtilResult {
    case success, error, denied
}

//相册操作工具类
class PhotoAlbumUtil: NSObject {
    
     public typealias completion = ((_ result: PhotoAlbumUtilResult) -> ())
    //判断是否授权
    class func isAuthorized() -> Bool {
        return PHPhotoLibrary.authorizationStatus() == .authorized ||
            PHPhotoLibrary.authorizationStatus() == .notDetermined
        
    }
    
    //保存图片到相册
    class func saveImageInAlbum(image: UIImage, albumName: String,
                                completion: completion?) {
        //权限验证
        if !isAuthorized() {
            completion?(.denied)
            return
        }
        var assetAlbum: PHAssetCollection?
        
        //如果指定的相册名称为空，则保存到相机胶卷。（否则保存到指定相册）
        if albumName.isEmpty {
            let list = PHAssetCollection
                .fetchAssetCollections(with: .smartAlbum, subtype: .smartAlbumUserLibrary,
                                       options: nil)
            assetAlbum = list[0]
        } else {
            //看保存的指定相册是否存在
            let list = PHAssetCollection
                .fetchAssetCollections(with: .album, subtype: .any, options: nil)
            list.enumerateObjects({ (album, index, stop) in
                let assetCollection = album
                if albumName == assetCollection.localizedTitle {
                    assetAlbum = assetCollection
                    stop.initialize(to: true)
                }
            })
            //不存在的话则创建该相册
            if assetAlbum == nil {
                PHPhotoLibrary.shared().performChanges({
                    PHAssetCollectionChangeRequest
                        .creationRequestForAssetCollection(withTitle: albumName)
                }, completionHandler: { (isSuccess, error) in
                    self.saveImageInAlbum(image: image, albumName: albumName,
                                          completion: completion)
                })
                return
            }
        }
        
        //保存图片
        PHPhotoLibrary.shared().performChanges({
            //添加的相机胶卷
            let result = PHAssetChangeRequest.creationRequestForAsset(from: image)
            //是否要添加到相簿
            if !albumName.isEmpty {
                let assetPlaceholder = result.placeholderForCreatedAsset
                let albumChangeRequset = PHAssetCollectionChangeRequest(for:
                    assetAlbum!)
                albumChangeRequset!.addAssets([assetPlaceholder!]  as NSArray)
            }
        }) { (isSuccess: Bool, error: Error?) in
            if isSuccess {
                completion?(.success)
            } else{
                print(error!.localizedDescription)
                completion?(.error)
            }
        }
    }
}

PhotoAlbumUtil.saveImageInAlbum(image: image, albumName: "APP") { (result) in
    DispatchQueue.main.async {
        switch result{
        case .success:
            //"保存成功"
            break
        case .denied:
            //没有权限，去设置里打开权限
            let a = MyAlertController()
            a.addOKView("去设置"){ (a) in
                let url = URL(string: UIApplicationOpenSettingsURLString)
                if let url = url, UIApplication.shared.canOpenURL(url) {
                    if #available(iOS 10, *) {
                        UIApplication.shared.open(url, options: [:],
                                                  completionHandler: {
                                                    (success) in
                        })
                    } else {
                        UIApplication.shared.openURL(url)
                    }
                }
            }
            a.addCancelView()
            a.show(self,title: "没有相册权限",message: "请您到 \"设置\" -> \"APP\" 开启相册权限", style: .alert )
            break
        case .error:
            //"保存失败"
        }
    }
}