[mono] Implement Environment.GetFolderPath for Android

[EgorBo]

The following snippet:

var values = Enum.GetValues(typeof(global::System.Environment.SpecialFolder));
foreach (var sf in values)
{
    var path = global::System.Environment.GetFolderPath((global::System.Environment.SpecialFolder)sf);
    if (!string.IsNullOrEmpty(path))
    {
        Console.WriteLine($"{sf} = {path};");
    }
}

doesn't print anything for os=Android (all values are empty).
For reference, here is what current Xamarin.Android returns for my simple app:

Desktop = /data/user/0/com.companyname.Vederko/files/Desktop;
MyDocuments = /data/user/0/com.companyname.Vederko/files;
MyDocuments = /data/user/0/com.companyname.Vederko/files;
MyMusic = /data/user/0/com.companyname.Vederko/files/Music;
MyVideos = /data/user/0/com.companyname.Vederko/files/Videos;
DesktopDirectory = /data/user/0/com.companyname.Vederko/files/Desktop;
Fonts = /data/user/0/com.companyname.Vederko/files/.fonts;
Templates = /data/user/0/com.companyname.Vederko/files/Templates;
ApplicationData = /data/user/0/com.companyname.Vederko/files/.config;
LocalApplicationData = /data/user/0/com.companyname.Vederko/files/.local/share;
CommonApplicationData = /usr/share;
MyPictures = /data/user/0/com.companyname.Vederko/files/Pictures;
UserProfile = /data/user/0/com.companyname.Vederko/files;
CommonTemplates = /usr/share/templates;

[MaximLipnin]

When running the following as a functional test

// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

using System;
using System.Globalization;

public static class Program
{
    public static int Main(string[] args)
    {
        int result = 42;

        var values = Enum.GetValues(typeof(global::System.Environment.SpecialFolder));
        Console.WriteLine($"Start logging ==========");
        foreach (var sf in values)
        {
            var path = global::System.Environment.GetFolderPath((global::System.Environment.SpecialFolder)sf);
            if (!string.IsNullOrEmpty(path))
            {
                Console.WriteLine($"{sf} = {path};");
            }
        }

        Console.WriteLine($"Finish logging ==========");
        return result;
    }
}

I get the following output in the log:

07-26 12:22:13.823  7529  7548 I DOTNET  : Start logging ==========
07-26 12:22:13.862  7529  7548 I DOTNET  : MyDocuments = /data/user/0/net.dot.Android.Device_Emulator.EnvironmentGetFolderPath.Test/files;
07-26 12:22:13.862  7529  7548 I DOTNET  : MyDocuments = /data/user/0/net.dot.Android.Device_Emulator.EnvironmentGetFolderPath.Test/files;
07-26 12:22:13.866  7529  7548 I DOTNET  : UserProfile = /data/user/0/net.dot.Android.Device_Emulator.EnvironmentGetFolderPath.Test/files;
07-26 12:22:13.866  7529  7548 I DOTNET  : Finish logging ==========

It seems to be expected behavior.

[MaximLipnin]

On the other hand, looking at the entire list of special folder, it still consists mostly of empty values:

07-26 15:13:59.438  8827  8845 I DOTNET  : Start logging ==========
07-26 15:13:59.495  8827  8845 I DOTNET  : Desktop = ;
07-26 15:13:59.495  8827  8845 I DOTNET  : Programs = ;
07-26 15:13:59.495  8827  8845 I DOTNET  : MyDocuments = /data/user/0/net.dot.Android.Device_Emulator.EnvironmentGetFolderPath.Test/files;
07-26 15:13:59.495  8827  8845 I DOTNET  : MyDocuments = /data/user/0/net.dot.Android.Device_Emulator.EnvironmentGetFolderPath.Test/files;
07-26 15:13:59.495  8827  8845 I DOTNET  : Favorites = ;
07-26 15:13:59.495  8827  8845 I DOTNET  : Startup = ;
07-26 15:13:59.495  8827  8845 I DOTNET  : Recent = ;
07-26 15:13:59.495  8827  8845 I DOTNET  : SendTo = ;
07-26 15:13:59.495  8827  8845 I DOTNET  : StartMenu = ;
07-26 15:13:59.495  8827  8845 I DOTNET  : MyMusic = ;
07-26 15:13:59.495  8827  8845 I DOTNET  : MyVideos = ;
07-26 15:13:59.495  8827  8845 I DOTNET  : DesktopDirectory = ;
07-26 15:13:59.496  8827  8845 I DOTNET  : MyComputer = ;
07-26 15:13:59.496  8827  8845 I DOTNET  : NetworkShortcuts = ;
07-26 15:13:59.496  8827  8845 I DOTNET  : Fonts = ;
07-26 15:13:59.496  8827  8845 I DOTNET  : Templates = ;
07-26 15:13:59.496  8827  8845 I DOTNET  : CommonStartMenu = ;
07-26 15:13:59.496  8827  8845 I DOTNET  : CommonPrograms = ;
07-26 15:13:59.496  8827  8845 I DOTNET  : CommonStartup = ;
07-26 15:13:59.496  8827  8845 I DOTNET  : CommonDesktopDirectory = ;
07-26 15:13:59.496  8827  8845 I DOTNET  : ApplicationData = ;
07-26 15:13:59.496  8827  8845 I DOTNET  : PrinterShortcuts = ;
07-26 15:13:59.503  8827  8845 I DOTNET  : LocalApplicationData = ;
07-26 15:13:59.503  8827  8845 I DOTNET  : InternetCache = ;
07-26 15:13:59.503  8827  8845 I DOTNET  : Cookies = ;
07-26 15:13:59.503  8827  8845 I DOTNET  : History = ;
07-26 15:13:59.503  8827  8845 I DOTNET  : CommonApplicationData = ;
07-26 15:13:59.503  8827  8845 I DOTNET  : Windows = ;
07-26 15:13:59.503  8827  8845 I DOTNET  : System = ;
07-26 15:13:59.503  8827  8845 I DOTNET  : ProgramFiles = ;
07-26 15:13:59.503  8827  8845 I DOTNET  : MyPictures = ;
07-26 15:13:59.504  8827  8845 I DOTNET  : UserProfile = /data/user/0/net.dot.Android.Device_Emulator.EnvironmentGetFolderPath.Test/files;
07-26 15:13:59.504  8827  8845 I DOTNET  : SystemX86 = ;
07-26 15:13:59.504  8827  8845 I DOTNET  : ProgramFilesX86 = ;
07-26 15:13:59.504  8827  8845 I DOTNET  : CommonProgramFiles = ;
07-26 15:13:59.504  8827  8845 I DOTNET  : CommonProgramFilesX86 = ;
07-26 15:13:59.504  8827  8845 I DOTNET  : CommonTemplates = ;
07-26 15:13:59.504  8827  8845 I DOTNET  : CommonDocuments = ;
07-26 15:13:59.504  8827  8845 I DOTNET  : CommonAdminTools = ;
07-26 15:13:59.504  8827  8845 I DOTNET  : AdminTools = ;
07-26 15:13:59.504  8827  8845 I DOTNET  : CommonMusic = ;
07-26 15:13:59.504  8827  8845 I DOTNET  : CommonPictures = ;
07-26 15:13:59.504  8827  8845 I DOTNET  : CommonVideos = ;
07-26 15:13:59.504  8827  8845 I DOTNET  : Resources = ;
07-26 15:13:59.504  8827  8845 I DOTNET  : LocalizedResources = ;
07-26 15:13:59.504  8827  8845 I DOTNET  : CommonOemLinks = ;
07-26 15:13:59.504  8827  8845 I DOTNET  : CDBurning = ;
07-26 15:13:59.504  8827  8845 I DOTNET  : Finish logging ==========

[EgorBo]

Related PR but for iOS: #34022

[directhex]

Is HOME set on Android? It would explain why UserProfile and MyDocuments are set, but nothing else is