Visual Studio Code – Repeatedly save to external storage on Android in Xamarin Forms

I am running into an issue in a Xamarin Forms project I am working on, building and using on UWP and Android (don’t care about iOS currently). My app is one which connects to a Bluetooth device to record data, stores it within the app, and exports the data into a .txt file or similar that is used for other purposes outside the app. On Android, targeting either Android 11 or Android 12.

I am working with Xamarin 17.4.0.301, Visual Studio 17.4.0, and .NET Framework 4.8.04084, and Xamarin.Android SDK 13.1.0.1.

My issue is trying to save to a file repeatedly that is accessible. Currently, I use a file hidden in the app’s internal storage, using a filepath like this:

string fileName = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData), "data.txt");

This of course works on both UWP and Android; however, since it is internal, it cannot be accessed by a file explorer on Android. To be seen on Android, I have to export it from the app into a file explorer app, using code like this, where the command is tied to a button press:

OnShareDataCommand = new Command(ShareDataButtonClick);
...
private async void ShareDataButtonClick() {
            string fileName = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData), "data.txt");
            await Share.RequestAsync(new ShareFileRequest {
                Title = "Share Data",
                File = new ShareFile(fileName)
            });
        }

This requires a user to press the button to export. My desire is for the system to automatically make a file somewhere accessible in the file explorer (like a Downloads folder) and continuously save to it when the function is called. To do this, I have enable access to external storage as such in the Android Manifest:

<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>

But I am running into issues accessing it. The first is when I try to create a filepath that is in external storage like this, based on this StackOverflow question:

var fullPath = Path.Combine(Android.OS.Environment.ExternalStorageDirectory.AbsolutePath, "file_name.txt");

When I do this, it says Android is not in the context. I imagine this is because I am in Xamarin Forms building for multiple platforms. How can I fix this? How can I access Android’s External Storage while in Xamarin Forms? Can I make a platform specific function, and if so, how do I go about it?

This Xamarin forums solution did not work.

I have tried using this line from the External Storage for Xamarin.Android guide, which also does not work because it says Environment does not have the method used:

Environment.GetExternalStoragePublicDirectory(Environment.DirectoryDocuments).AbsolutePath

Any advice? I do not want to make it an Android specific app, as I need the UWP functionality, but I could make a platform-specific save function.