问题

我正在使用Xamarin.Forms编写代码以在iOS平台下载文件。它可以成功下载文件，没有任何错误。但是，在下载完成后，我无法在我的苹果设备上找到已下载的文件。

在调试过程中，我发现它显示的路径是：

/var/mobile/Containers/Data/Application/1234567A-B8CD-9EF9-C850-9G73587DC7C/Documents/XF_Downloads/hausmann_abcd.jpg

文件保存在哪个位置？以下是相应的图像。

我已经编写了以下代码来实现这一功能：

public class IosDownloader : IDownloader
{
    public event EventHandler<DownloadEventArgs> OnFileDownloaded;

    public void DownloadFile(string url, string folder)
    {
        string pathToNewFolder = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.Personal), folder);
        Directory.CreateDirectory(pathToNewFolder);

        try
        {
            WebClient webClient = new WebClient();
            webClient.DownloadFileCompleted += new AsyncCompletedEventHandler(Completed);
            string pathToNewFile = Path.Combine(pathToNewFolder, Path.GetFileName(url));
            webClient.DownloadFileAsync(new Uri(url), pathToNewFile);
        }
        catch (Exception ex)
        {
            if (OnFileDownloaded != null)
                OnFileDownloaded.Invoke(this, new DownloadEventArgs(false));
        }
    }

    private void Completed(object sender, AsyncCompletedEventArgs e)
    {
        if (e.Error != null)
        {
            if (OnFileDownloaded != null)
                OnFileDownloaded.Invoke(this, new DownloadEventArgs(false));
        }
        else
        {
            if (OnFileDownloaded != null)
                OnFileDownloaded.Invoke(this, new DownloadEventArgs(true));
        }
    }
}

<details>
<summary>英文:</summary>

I am using Xamarin.Forms and written the code to download the file for the iOS 
platform. It is downloading the file successfully without any error. But after downloading it, I am not able to find the downloaded file in my apple device.

During debugging I found that it is showing 

    /var/mobile/Containers/Data/Application/1234567A-B8CD-9EF9-C850-9G73587DC7C/Documents/XF_Downloads/hausmann_abcd.jpg

path. So at which location file get saved? below is the image for the same. 

[![enter image description here][1]][1]


  [1]: https://i.stack.imgur.com/APNF6.png

I have written below code for this

    public class IosDownloader : IDownloader
    {
        public event EventHandler&lt;DownloadEventArgs&gt; OnFileDownloaded;

        public void DownloadFile(string url, string folder)
        {
            string pathToNewFolder = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.Personal), folder);
            Directory.CreateDirectory(pathToNewFolder);

            try
            {
                WebClient webClient = new WebClient();
                webClient.DownloadFileCompleted += new AsyncCompletedEventHandler(Completed);
                string pathToNewFile = Path.Combine(pathToNewFolder, Path.GetFileName(url));
                webClient.DownloadFileAsync(new Uri(url), pathToNewFile);
            }
            catch (Exception ex)
            {
                if (OnFileDownloaded != null)
                    OnFileDownloaded.Invoke(this, new DownloadEventArgs(false));
            }
        }

        private void Completed(object sender, AsyncCompletedEventArgs e)
        {
            if (e.Error != null)
            {
                if (OnFileDownloaded != null)
                    OnFileDownloaded.Invoke(this, new DownloadEventArgs(false));
            }
            else
            {
                if (OnFileDownloaded != null)
                    OnFileDownloaded.Invoke(this, new DownloadEventArgs(true));
            }
        }
    }


</details>


# 答案1
**得分**: 3

当文件保存在应用程序中时，它是应用程序沙盒内的临时URL。要使此图像文件通过苹果的`Photos`公开访问，您需要使用本机代码执行请求，将新的`PHImageAsset`添加到照片库中。

在表单中，您需要访问本机框架，因此必须运行本机代码。如果您不知道如何操作，网上有很多示例可供参考。但如果您想在共享代码框架中运行本机代码，这里是一个简介：https://learn.microsoft.com/en-us/xamarin/xamarin-forms/app-fundamentals/dependency-service/introduction

以下是一个示例，演示如何将临时文件URL保存到`Photos`框架中，一旦您能够使用本机的`Xamarin.iOS`框架编写代码：

```csharp
public void AddImageUrlToPhotosLibrary(string urlToSaveToPhotos)
{
    PHPhotoLibrary.SharedPhotoLibrary.PerformChanges(() => {

        //这是绑定到本机的https://developer.apple.com/documentation/photokit/phassetchangerequest/1624060-creationrequestforasset
        //参数是图像路径的NSURL。
        PHAssetChangeRequest.FromImage(new NSUrl(urlToSaveToPhotos));

    }, (completed, error) => {

        if (completed)
        {
            if (error != null)
            {
                Console.WriteLine($"Failed saving image asset {error.LocalizedDescription}");
            } else
            {
                Console.WriteLine($"Successfully saved image to photos library.");
            }
        }
    });
}

请注意，上述代码是使用C#编写的，并使用Xamarin.iOS框架与苹果的Photos框架进行交互。

    public void AddImageUrlToPhotosLibrary(string urlToSaveToPhotos)
    {
        PHPhotoLibrary.SharedPhotoLibrary.PerformChanges(() => {

            //This is bound to native https://developer.apple.com/documentation/photokit/phassetchangerequest/1624060-creationrequestforasset
            //Parameter is an NSURL of path to image.
            PHAssetChangeRequest.FromImage(new NSUrl(urlToSaveToPhotos));

        }, (completed, error) => {

            if (completed)
            {
                if (error != null)
                {
                    Console.WriteLine($"Failed saving image asset {error.LocalizedDescription}");
                } else
                {
                    Console.WriteLine($"Successfully saved image to photos library.");
                }
            }
        });
    }

答案2

得分: 1

无法在我的苹果设备中找到已下载的文件。

如果您使用模拟器，可以通过在Mac中输入以下路径直接找到文件夹：

您的Mac --> 选择Finder --> 然后打开前往菜单 --> 单击前往文件夹，如我在此帖子中所描述的：

我在iPhone模拟器上哪里可以找到MyDocuments文件夹？

如果您在真实设备上安装了应用程序，可以按照以下线程中描述的步骤浏览文件：

Xcode --> 设备和模拟器 --> 下载容器，如此线程中所述：

浏览由我开发的iOS应用程序在设备上创建的文件，下载容器后，您可以右键单击它并选择显示包内容。然后您可以看到文件夹。

您还可以通过项目中的路径访问文件。