在Xamarin.Forms中，如何将文件从隔离存储复制到“下载"文件夹? [英] In Xamarin.Forms, how can I copy a file from the isolated storage to the Downloads folder?

问题描述

我正在尝试将数据库文件从隔离存储区复制到下载"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).

当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，这是下载文件夹的名称.
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:找不到目标目录: 下载.

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

我曾经尝试过这样的斜杠:/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，您确实需要权限才能写入外部存储.

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

您可以自行获得所需的运行时间许可:

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

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

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

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

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

2nd)一旦用户接受可以写入外部存储的操作，就可以使用:

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

要获取设备公共下载文件夹的路径，即使用Forms的依赖项服务，请执行以下操作:

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

您最终得到类似的东西:

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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