using swift 2.0 save photo to custom album

新建了一个CustomAblum类，写成了单例, 这个写单例的方式是swift中的最好的一种方式：

    static let sharedInstance = CustomAblum()

定义几个变量：

    var assetCollection: PHAssetCollection!
    var albumFound : Bool = false
    var photosAsset: PHFetchResult!
    var collection: PHAssetCollection!
    var assetCollectionPlaceholder: PHObjectPlaceholder!
    static let albumName = "爱拍美图"

在初始化方法中创建自定义相册

init() {
        self.createAlbum()
    }

private func createAlbum() {
        let fetchOptions = PHFetchOptions()
        fetchOptions.predicate = NSPredicate(format: "title = %@", CustomPhotoAlbum.albumName)
        let collection : PHFetchResult = PHAssetCollection.fetchAssetCollectionsWithType(.Album, subtype: .Any, options: fetchOptions)
        
        if let _: AnyObject = collection.firstObject {
            self.albumFound = true
            assetCollection = collection.firstObject as! PHAssetCollection
        } else {
            PHPhotoLibrary.sharedPhotoLibrary().performChanges({
                let createAlbumRequest : PHAssetCollectionChangeRequest = PHAssetCollectionChangeRequest.creationRequestForAssetCollectionWithTitle(CustomPhotoAlbum.albumName)
                self.assetCollectionPlaceholder = createAlbumRequest.placeholderForCreatedAssetCollection
                }, completionHandler: { success, error in
                    self.albumFound = (success ? true: false)
                    
                    if (success) {
                        let collectionFetchResult = PHAssetCollection.fetchAssetCollectionsWithLocalIdentifiers([self.assetCollectionPlaceholder.localIdentifier], options: nil)
                        print(collectionFetchResult)
                        self.assetCollection = collectionFetchResult.firstObject as! PHAssetCollection
                    }
            })
        }
    }

写一个saveImage方法：

func saveImage(image: UIImage) {
        if self.assetCollection != nil {
            PHPhotoLibrary.sharedPhotoLibrary().performChanges({
                let assetChangeRequest = PHAssetChangeRequest.creationRequestForAssetFromImage(image)
                let assetPlaceholder = assetChangeRequest.placeholderForCreatedAsset
                let albumChangeRequest = PHAssetCollectionChangeRequest(forAssetCollection: self.assetCollection)
                albumChangeRequest?.addAssets([assetPlaceholder!])
                }, completionHandler: nil)
        }
    }