How can I make my Android app read and write a .txt file?

Question

I'm using Xamarin, C# and Monogame and I'm taking a fully-working Desktop game and porting it over to Android.

My problem is that I have this "Content folder" that you would always use in the Desktop version of the app. But I cannot access it or any other folder through the code directly using Android. basicShader = new Effect(game1.GraphicsDevice,System.IO.File.ReadAllBytes("Content/TextureShader.mgfxo"));

This works just fine in the Desktop app but throws System.IO.DirectoryNotFoundException:'Could not find a part of the path "/Content/TextureShader.mgfxo".' on Android.

I'd like to mention that I already had the code and the project working perfectly when it was a desktop program. I also have a private class-level variable string[] list_of_files and in the constructor, I had the line list_of_files = Directory.GetFiles("./Content","*.txt"); This is for saving and loading player data. It may have been rudimentary but I had a fully functioning program that saved and loaded data on my computer. I am transitioning this program to be an Android app and this is the only part of the project that isn't working. When I run the code as it was originally written, I get "System.IO.DirectoryNotFoundException: 'Could not find a part of the path '/Content'.' ".

I've tried playing around with trying to read the contents of different folders. I've messed around with different paths, including the Resources folder instead. I added <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" /> to my manifest. I know that I'm trying to access internal storage, not external, so I also tried <uses-permission android:name="android.permission.READ_INTERNAL_STORAGE" /> just to see if that might work. Nothing works.

In another stack overflow post, a guy commented:

For the people who are facing NullPointerException - you are trying to access the files in the app's internal storage which are private sorry you can't do that. – coderpc Jun 23, 2017 at 16:00

I cannot imagine why this would be true. Why would a programmer not be able to write a program that can access it's own internal storage? That makes no sense to me. Obviously my app needs to be able to read and write it's own internal storage! And if this is true, then how else can I save persistent data on my phone? I don't want a database or a shared thingamabobber that uses key-value pairs, I have a self-made system that works as a text file and I want to continue to use it. I refuse to believe that an Android app can't keep track of a simple .txt file in one of it's own folders, that's just too hard for me to imagine. It can't be true.

I wanted to ask the commenter about his comment but Stack Overflow wouldn't let me because I don't have over 50xp.

Answer 1

Just like CommonsWare sayed, you can use the Intent.ActionOpenDocument to get the uri of the file. Such as

 static readonly int READ_REQUEST_CODE = 1337;
 Intent intent = new Intent(Intent.ActionOpenDocument);
 intent.AddCategory(Intent.CategoryOpenable);
 intent.SetType("*/*");
 StartActivityForResult(intent, READ_REQUEST_CODE); 

And override the OnActivityResult method:

 if (requestCode == READ_REQUEST_CODE && resultCode == Result.Ok)
        {
            // The document selected by the user won't be returned in the intent.
            // Instead, a URI to that document will be contained in the return intent
            // provided to this method as a parameter.  Pull that uri using "resultData.getData()"
            if (data != null)
            {
                Android.Net.Uri uri = data.Data;
                DocumentFile documentFile = DocumentFile.FromSingleUri(this.ApplicationContext,uri);
                // Then you can operate the file with input and output stream
            }
        }

More information please check the simple on the github: https://github.com/xamarin/monodroid-samples/blob/main/StorageClient/StorageClientFragment.cs

In addition, if you can ensure the file's path. You can use the StreamWriter and the StreamReader to write and read the file. Such as:

using (StreamWriter sw = new StreamWriter(path))
            {
                sw.WriteLine(content);
            }

Furthermore, you can try to create the content folder and the txt file in the Android with the following code.

var filename1 = Android.App.Application.Context.GetExternalFilesDir(System.DateTime.Now.ToString("Content")).AbsolutePath;
var filename = System.IO.Path.Combine(filename1,  "xxx.txt");
using (System.IO.FileStream os = new System.IO.FileStream(filename, System.IO.FileMode.Create)) 
{

}

The folder and the files created by this way belongs to the app and you can access it easily.

You can read the official document about the storage in the Android.

Link : https://developer.android.com/training/data-storage/shared/documents-files