首次运行时，将照片保存在自定义专辑中

Question

嗨，我正在创建一个相册应用程序作为一个学习项目，而我对PHPhotoLibrary.shared().performChangesAndWait有一些问题；主要问题是，当具有PHPhotoLibrary.shared().performChangesAndWait代码的方法saveImage时；在PHPhotoLibrary.shared().performChangesAndWait完成保存图像之前，该方法退出。即使我使用的是performChangesAndWait方法，根据文档应该等待直到结束。

，似乎代码也会异步执行。 。

这是我的班级中的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
}

基本上再次，当应用程序首次运行时，返回结果在保存图像块完成之前被执行。

有什么办法可以强迫保存图的方法实际等到perferchangesandwait方法实际完成？

事先感谢您的帮助。

Answer 1

performChangesAndWait是一种异步回调方法。performChangesAndWait内部的result上的更改不会在返回时反映，因为这两个在不同的线程中。

等待saveImage方法完成的一种方法是实现回调。类似：

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。

Answer 2

这是解决方案（swift 5）：

@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...")
        }
    }
}