swift – 在应用程序处于后台时访问PHPhotoLibrary

我有一个NSURLDownloadTask,可以在后台成功下载文件(大图像或视频文件).我成功复制了网址并调用此功能将我的网址保存到照片库.如您所见,我想发送UILocalNotification以通知用户他们的下载已完成.

我的问题是虽然PHP应用程序处于后台时会调用PHPhotoLibrary.sharedPhotoLibrary().performChanges,但它的完成块不会. (但它要求应用程序重新回到前台)我试着通过评论抓住主线程,看看是否有帮助,但事实并非如此.并且我不想在完成块之前发送本地通知,因为我想告诉用户下载成功/失败的通知.

我想我可以在NSURLDownloadDelegateTask方法中发送通知.这将让用户知道文件已成功下载,但不知道是否将其保存到他们的照片是成功的.我不想告诉我的用户他们的下载成功,然后他们无法在他们的照片库中找到它.

这是我访问和修改照片库的代码.

func saveURLToPhotosLibrary(url: NSURL, fileName: String) {

        if let fileExtension = url.pathExtension {
            PHPhotoLibrary.sharedPhotoLibrary().performChanges({

                let fileUnmanagedIDTag = UTTypeCreatePreferredIdentifierForTag(kUTTagClassFilenameExtension, fileExtension, nil)

                let fileIDTag = fileUnmanagedIDTag?.takeRetainedValue()
                if let fileUTType = fileIDTag {
                    if UTTypeConformsTo(fileUTType, kUTTypeImage) {
                        PHAssetChangeRequest.creationRequestForAssetFromImageAtFileURL(url)
                    } else if UTTypeConformsTo(fileUTType, kUTTypeMovie){
                        PHAssetChangeRequest.creationRequestForAssetFromVideoAtFileURL(url)
                    }
                } else {
                    print("Error getting type of file from download")
                }

            }) { (success, error) in
                //dispatch_async(dispatch_get_main_queue(), {

                    if success {
                        print("finished")
                        self.sendLocalNotification(downloadSuccessful: true, error : nil, fileName: fileName)
                    } else {
                        if let error = error {
                            self.sendLocalNotification(downloadSuccessful: false, error : error, fileName: fileName)
                        }
                    }
                //})
            }
        }
    }

好吧找到了我的工作解决方案.发现应用程序在没有运行代码后立即暂停,因此应用程序在我的完成处理程序准备好被调用时被暂停.我使用UIApplications共享实例来创建一个新的后台任务.这使我的应用程序有足够的时间来调用完成处理程序.然后我在收到通知后立即结束后台任务.

func saveURLToPhotosLibrary(url: NSURL, fileName: String) {

    //Returns id to later be passed into method that ends task.
    let backgroundID : Int = UIApplication.sharedApplication().beginBackgroundTaskWithName("Save to Photo Library Task") {
        print("Background task expired")
    }

    if let fileExtension = url.pathExtension {
        PHPhotoLibrary.sharedPhotoLibrary().performChanges({

            let fileUnmanagedIDTag = UTTypeCreatePreferredIdentifierForTag(kUTTagClassFilenameExtension, fileExtension, nil)

            let fileIDTag = fileUnmanagedIDTag?.takeRetainedValue()
            if let fileUTType = fileIDTag {
                if UTTypeConformsTo(fileUTType, kUTTypeImage) {
                    PHAssetChangeRequest.creationRequestForAssetFromImageAtFileURL(url)
                } else if UTTypeConformsTo(fileUTType, kUTTypeMovie){
                    PHAssetChangeRequest.creationRequestForAssetFromVideoAtFileURL(url)
                }
            } else {
                print("Error getting type of file from download")
            }


        }) { (success, error) in

                if success {
                    print("finished")
                    self.sendLocalNotification(downloadSuccessful: true, error : nil, fileName: fileName)
                } else {
                    if let error = error {
                        self.sendLocalNotification(downloadSuccessful: false, error : error, fileName: fileName)
                    }
                }
            //End background task here passing in id of task from earlier.
            UIApplication.sharedApplication().endBackgroundTask(backgroundID)
        }
    }
}