I am writing a simple test application on Windows Form. I need to pass the configuration via IOptions. There are two values in the configuration: AccessKey and SecretKey. I will need to get these values on the main form. Here is my code:

//appsettings.json:

{
  "ConnectionString:AccessKey": "FDJKSFDJF",
  "ConnectionString:SecretKey": "KSDHFKDJF"
}


public class ConnectionString
{
    public string? AccessKey { get; set; }
    public string? SecretKey { get; set; }
}


 public static class Startup
 {
        public static IServiceProvider? ServiceProvider;
        private static readonly IConfiguration Configuration;
        public static ConnectionString connectionString { get; set; }

        static Startup()
        {
           var builder = new ConfigurationBuilder().AddJsonFile("appsettings.json");
           var AppConfiguration = builder.Build();
        }
 }


//the class in which I need to get the values:

public partial class MainForm : Form
    {
       public ConnectionString connectionString { get; }

        public MainForm()
        {
            InitializeComponent();

            MessageBox.Show(connectionString.AccessKey);
           
        }

        public MainForm(IOptions<ConnectionString> options)
        {
            connectionString = options.Value;
        }
}

with this code, I get the error System.NullReferenceException: "Object reference not set to an instance of an object.". I understand that my file .json has nothing to do with my class right now. help meeee.

CodePudding user response：

Here is an example of how to use DI together with windows forms application.

internal static class Program
{
    public static IHost? CurrentHost { get; private set; }
    
    /// <summary>
    ///  The main entry point for the application.
    /// </summary>
    [STAThread]
    static void Main()
    {
        // To customize application configuration such as set high DPI settings or default font,
        // see https://aka.ms/applicationconfiguration.
        ApplicationConfiguration.Initialize();       

        CurrentHost = Host.CreateDefaultBuilder()
                .ConfigureServices((context, services) =>
                {
                    //Registers a config instance which TOptions will bind against.
                    services.Configure<ConnectionString>(context.Configuration.GetSection("ConnectionStrings"));
                    services.AddScoped<MainForm>();                    
                })
                //sets up the configuration
                .ConfigureAppConfiguration(context => BuildConfig(context))
                .Build();

        using IServiceScope serviceScope = CurrentHost.Services.CreateScope();
        IServiceProvider provider = serviceScope.ServiceProvider;
        var mainForm = provider.GetRequiredService<MainForm>();
        Application.Run(mainForm);
    }

    static void BuildConfig(IConfigurationBuilder builder)
    {
        builder.SetBasePath(Directory.GetCurrentDirectory())
            .AddJsonFile("appsettings.json", optional: false, reloadOnChange: true)
            .AddJsonFile($"appsettings.{Environment.GetEnvironmentVariable("ASPNETCORE_ENVIRONMENT") ?? "Production"}.json", optional: true)
            .AddEnvironmentVariables();
    }
}

And then you can inject IOptions<ConnectionString> from the constructor of the MainForm

public partial class MainForm : Form
{
    public MainForm(IOptions<ConnectionString> options)
    {
        var connString = options.Value;
        InitializeComponent();        
    }
}