Maui throws FileNotFoundException only when linking to JSON file from external assembly

Question

I have two projects in a single solution:

• class library project MyLibrary that contains appsettings.json + Settings.cs
• MAUI project MyMobile that references MyLibrary.

MyLibrary

{
    "Settings": {
        "Id": 1,
        "Message": "Hello World"
    }
}

namespace MyLibrary;
public class Settings
{
    public const string SECTION = nameof(Settings);

    public int Id { get; set; }
    public string Message { get; set; } = null!;
}

MyMobile

public partial class App : Application
{
    public App(IOptions<Settings> settings)
    {
        InitializeComponent();
        MainPage = new MainPage(settings.Value.Message);
    }
}

public partial class MainPage : ContentPage
{
    public MainPage(string message)
    {
        InitializeComponent();
        OutputLabel.Text = message;
    }  
}

public static MauiApp CreateMauiApp()
{
    var builder = MauiApp.CreateBuilder();

    using var stream = FileSystem.OpenAppPackageFileAsync("appsettings.json").Result;
    builder.Configuration.AddJsonStream(stream); // Microsoft.Extensions.Configuration.Json
    builder.Services.AddOptions<Settings>().BindConfiguration(Settings.SECTION);// Microsoft.Extensions.Options.ConfigurationExtensions
    

   // others ...
}

Question

• If I add appsettings.json to Resources/raw with Build Action : MauiAsset, it works.
• But if I add as link appsettings.json to Resources/raw with Build Action : MauiAsset, it does NOT work.

System.AggregateException: 'One or more errors occurred. (The system cannot find the file specified. An item cannot be found with the specified name (appsettings.json).)' FileNotFoundException: The system cannot find the file specified.

What am I missing here?

Edit:

Answer 1

But if I add as link appsettings.json to Resources/raw with Build Action : MauiAsset, it does NOT work.

I created a new project with the code you provided and reproduce your problem. What I found:

The appsettings.json file's build action in the Class Library is set as None. When you add it as link and set its build action As MauiAsset in the Maui project, the source file's build action is still None.

So you can fix it by the following steps:

1. Set the appsettings.json file's build action as MauiAsst in the class library.
2. Remove the appsettings.json and add it again in the Maui project.

In addition, adding the appsettings.json directly instead of as link is a better choice.

Set by changing csproj file in the class library:

<ItemGroup>
  <MauiAsset Include="appsettings.json" />
</ItemGroup>

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The debugging result image: