How to correctly access existing files in the app data folder created with an Xamarin.Forms app inside a migrated MAUI app?

[ewerspej]

I've already asked this in a Stack Overflow question, but it seems appropriate to also ask this here:

Is there an official migration path for accessing files in the local application data folder on Android?

Consider the following code in a Xamarin.Forms and a migrated .NET MAUI app:

public static string DatabasePath
{
    get
    {
        var basePath = Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData);
        return Path.Combine(basePath, "mydb.db3");
    }
}

In Xamarin.Forms, the resulting path on Android is (just like it's documented here):

/data/user/0/my.app/files/.local/share/mydb.db3

However, when using the exact same code in MAUI, the resulting path on Android is:

/data/user/0/my.app/files/mydb.db3

I've resolved this issue by appending ".local/share" to the provided path on Android:

public static string DatabasePath
{
    get
    {
        var basePath = Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData);
        
        // upgrade scenario for Xamarin.Forms to MAUI
        if (!basePath.Contains(".local/share") && File.Exists(Path.Combine(basePath, ".local/share", DatabaseFilename)))
        {
            basePath = Path.Combine(basePath, ".local/share");
        }

        return Path.Combine(basePath, "mydb.db3");
    }
}

Note: The code above is just exemplary, the actual solution would use preprocessor directives or multi-targeting and constants for the file paths and a const ".local/share" string.

What's the recommended course of action? Is this the way to migrate Xamarin.Forms apps to .NET MAUI when trying to access existing files in an upgraded app?

[maonaoda]

v8.0.4
https://github.com/dotnet/runtime/blob/2d7eea252964e69be94cb9c847b371b23e4dd470/src/libraries/System.Private.CoreLib/src/System/Environment.Android.cs#L50-L58

[ewerspej]

How does that answer my question about migrating paths from XF to MAUI?

[bsloehr]

@ewerspej Thanks for bringing this to light. This is a huge migration issue and I'm surprised (or maybe not at this point) that this topic is not getting any attention. Per the guidelines you posted, LocalApplicationData is the appropriate area for an app database. That pathway should not have changed without some sort of HUGE warning that this was happening.

[bsloehr]

Looks like this was reported here: #5900

[gaurav-bagga]

@ewerspej thanks for raising this issue, I am also facing the same issue as you have mentioned, however what I am observing is when I upgrade the app on a physical device from Xamarin to MAUI.NET, the path /data/user/0/com.myapp.example/files/.local/share/MySQLite.db3 gets wiped off. It does not exists at all.

I have added logging and when app starts up post update, the log says path does not exists. I am trying this from VS IDE in development. Moving across git branches first installing the app and adding some data, post that change branch again deploy it on the physical device and on load it logs "Path does not exists".

I am on .net-8 and I am stuck what can be done when the whole folder goes away!

Others reading this, please advise do you also face this issue where the entire folder simply vanishes.

So far I have tried this in Debug mode, I still have to give Release mode a shot, to see if any difference is shown in the process.

[gaurav-bagga]

Oh it seems when deploying via VS IDE it is uninstalling it first, could see following in log trail.

/Users/abc/Library/Developer/Xamarin/android-sdk-macosx/platform-tools/adb -s <device id> shell cmd package uninstall com.myapp.example

[gaurav-bagga]

FYI: The above log trace was when I was deploying in release mode, in debug mode I don't see it. Log is from "Deploying to Device" window.

[ewerspej]

I think you need to enable Options -> Xamarin -> Android settings -> Preserve application data cache on device between deploys in Visual Studio so that it keeps the local app data between deployments.

For me, the local app data is preserved and upgrading an app from XF to MAUI also works, the local app data folder just isn't where it's expected to be.

[gaurav-bagga]

@ewerspej Thanks for the response, I'll check out settings you have provided.