Swift3 首次运行时，在自定义相册中保存照片失败

您好，我正在创建一个相册应用程序作为一个学习项目，我在PHPhotoLibrary.shared（）中遇到了一些问题。PerformChanges和Wait；主要问题是，当方法saveImage时，它具有

PHPhotoLibrary.shared（）.performchange和wait

code；方法在

PHPhotoLibrary.shared（）完成保存图像之前退出。即使在我使用
performChangesAndWait
方法时，代码似乎也是异步执行的，根据文档说明，应该等到它完成

下面是我的类中saveImage方法的代码：

func saveImage(_ image: UIImage) ->Bool {
    print("Executing saveImage")
    var result:Bool = false
    if assetCollection == nil {
        print("the album is nil")
        return result
    }
    print("saveImage: we will start saving the image")
    //TODO: the return false is happening before the photo is save.
    do
    {
        try PHPhotoLibrary.shared().performChangesAndWait({
            let assetChangeRequest = PHAssetChangeRequest.creationRequestForAsset(from: image)
            let assetPlaceHolder = assetChangeRequest.placeholderForCreatedAsset
            let albumChangeRequest = PHAssetCollectionChangeRequest(for: self.assetCollection)
            let enumeration: NSArray = [assetPlaceHolder!]
            albumChangeRequest!.addAssets(enumeration)
            print("saveImage: image was save without issues")
            result = true
            print("saveImage: result value after saving the image: \(result)")
        })
    }
    catch let error
    {
        result = false
        print("saveImage: there was a problem: \(error.localizedDescription)")
    }


    print("saveImage: result value before exiting the method: \(result)")
    return result

}

基本上，当应用程序第一次运行时，返回结果在保存图像块完成之前执行

有没有办法强制saveImage方法实际等待，直到performchanges和wait方法实际完成？

提前感谢您的帮助。
PerformChanges和Wait

是一种异步回调方法。在

performchange和wait

内部

result

上所做的更改不会在返回时反映出来，因为这两个线程位于不同的线程中

等待

saveImage

方法完成的一种方法是实现回调。比如：

func saveImage(_ image: UIImage, callback: @escaping(_ result: Bool)->Void) {
    print("Executing saveImage")

    if assetCollection == nil {
        print("the album is nil")
        callback(false)
    }
    print("saveImage: we will start saving the image")
    //TODO: the return false is happening before the photo is save.
    do {
        try PHPhotoLibrary.shared().performChangesAndWait({
            let assetChangeRequest = PHAssetChangeRequest.creationRequestForAsset(from: image)
            let assetPlaceHolder = assetChangeRequest.placeholderForCreatedAsset
            let albumChangeRequest = PHAssetCollectionChangeRequest(for: self.assetCollection)
            let enumeration: NSArray = [assetPlaceHolder!]
            albumChangeRequest!.addAssets(enumeration)
            print("saveImage: image was save without issues")

            callback(true)
        })
    }
    catch let error {
        print("saveImage: there was a problem: \(error.localizedDescription)")
        callback(false)
    }
}

让我们知道您得到了什么。

以下是解决方案（Swift 5）：

---

我知道此解决方案在“结果”Bool中为您提供了良好的结果反馈，但如何防止第一个saveImage失败？@drewster，问题不在于save image功能，而是刷新问题。

@objc private func handleSavePhoto() {

    guard let previewImage = self.photoImageView.image else { return }

    PHPhotoLibrary.requestAuthorization { (status) in
        if status == .authorized {
            do {
                try PHPhotoLibrary.shared().performChangesAndWait {
                    PHAssetChangeRequest.creationRequestForAsset(from: previewImage)
                }
            } catch let error {
                print("failed to save photo in library: ", error)
            }
        } else {
            print("Something went wrong with permission...")
        }
    }
}