如何将文件从独立存储复制到下载文件夹? [英] How can I copy a file from the isolated storage to the Downloads folder?

问题描述

我正在尝试将我的数据库文件从独立存储复制到下载文件夹(或用户可以访问的任何文件夹).

I'm trying to copy my database file from the isolated storage to the Download folder (or any folder that the user can access).

目前我的数据库存储在:

Currently my database is stored in:

/data/user/0/com.companyname.appname/files/Databases/MyDatabase.db

我尝试使用此代码:

public string GetCustomFilePath(string folder, string filename)
{
    var docFolder = System.Environment.GetFolderPath(System.Environment.SpecialFolder.Personal);
    var libFolder = Path.Combine(docFolder, folder);

    if (!Directory.Exists(libFolder))
        Directory.CreateDirectory(libFolder);

    return Path.Combine(libFolder, filename);
}


var bas = GetDatabaseFilePath("MyDatabase.db");
var des = Path.Combine(Android.OS.Environment.DirectoryDownloads, "MyDatabase.db");
File.Copy(bas, des);

Android.OS.Environment.DirectoryDownloads 属性返回路径 Download，即下载文件夹的名称.
但是 File.Copy() 抛出一个异常告诉

The Android.OS.Environment.DirectoryDownloads property returns the path Download, which is the name of the downloads folder.
But File.Copy() throws an exception telling

System.IO.DirectoryNotFoundException:未找到目标目录:下载.

System.IO.DirectoryNotFoundException: Destination directory not found: Download.

我之前尝试过像这样使用斜杠:/Download/MyDatabase.db 没有运气.

I tried to use a slash before like this: /Download/MyDatabase.db with no luck.

有没有办法复制这样的文件?我需要任何许可吗?

Is there any way to copy a file like that? Do I need any permission?

推荐答案

1st) 是的，您确实需要写入外部存储的权限.

1st) Yes, you do need permissions to write to external storage.

您可以通过自己动手获得所需的运行时权限:

You can get the runtime time permission required by doing it yourself:

• https://devblogs.microsoft.com/xamarin/requesting-runtime-permissions-in-android-marshmallow/

或者通过第三方插件，例如 James Montemagno 的 PermissionsPlugin

Or via a 3rd-party plugin, such as James Montemagno's PermissionsPlugin

• https://github.com/jamesmontemagno/PermissionsPlugin

2nd) 一旦您的用户接受可以写入外部存储，您可以使用:

2nd) Once your user accepts that it is ok to write to external storage, you can use:

Android.OS.Environment.ExternalStorageDirectory.AbsolutePath, Android.OS.Environment.DirectoryDownloads

获取设备公共下载文件夹的路径，即使用Forms的依赖服务:

To obtain the path of the device's public Download folder, i.e. using a Forms' dependency service:

public interface IDownloadPath
{
    string Get(); 
}

public class DownloadPath_Android : IDownloadPath
{
    public string Get()
    {
        return Path.Combine(Android.OS.Environment.ExternalStorageDirectory.AbsolutePath, Android.OS.Environment.DirectoryDownloads);
    }
}

• https://docs.microsoft.com/en-us/xamarin/xamarin-forms/app-fundamentals/dependency-service/introduction

你最终会得到类似的结果:

You end up with something like:

public void Handle_Button(object sender, System.EventArgs e)
{
    var fileName = "someFile.txt";
    using (var stream = File.Create(Path.Combine(FileSystem.CacheDirectory, fileName)))
    {
       // just creating a dummy file to copy (in the cache dir using Xamarin.Essentials
    }


    var downloadPath = DependencyService.Get<IDownloadPath>().Get();
    File.Copy(Path.Combine(FileSystem.CacheDirectory, fileName), downloadPath);
}

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