Is there a way to get AddOptionsWithValidateOnStart to work in Blazor Web Assembly?

[philipmorley]

Given:

• Framework: .NET 8.0
• Interactive render mode: WebAssembly
• Interactivity location: Global
• Include sample pages: true

I am trying to validate the appsettings.json file of my client web project using AddOptionsWithValidateOnStart.

Here is the client project wwwroot/appsettings.json:

{
  "Logging": {
    "LogLevel": {
      "Default": "Information",
      "Microsoft.AspNetCore": "Warning"
    }
  },
  "Foo": {
    "Bar": ""
  }
}

And FooSettings.cs:

using System.ComponentModel.DataAnnotations;
namespace ValidateOptions.Client;

public class FooSettings
{
  [Required]
  public string Bar { get; set; } = string.Empty;
}

And Program.cs:

using Microsoft.AspNetCore.Components.WebAssembly.Hosting;
using ValidateOptions.Client;

var builder = WebAssemblyHostBuilder.CreateDefault(args);

builder.Services
  .AddOptionsWithValidateOnStart<FooSettings>()
  .Bind(builder.Configuration.GetSection("Foo"))
  .ValidateDataAnnotations();

await builder.Build().RunAsync();

I was expecting/hoping that when I run the application I get an exception complaining that the Bar setting was missing. Instead I can navigate around the Home/Counter/Weather pages without error.

If I inject FooSettings into a page, for example:

@page "/counter"
@using Microsoft.Extensions.Options
@inject IOptions<FooSettings> AppSettings

<PageTitle>Counter</PageTitle>
<p>AppSettings = @AppSettings.Value.Bar</p>

Then I do get the desired behaviour when I navigate to the Counter page. How I can I get this behaviour across the entire website?

Demo repo here: https://github.com/philipmorley/BlazorValidateOptions

[nextfaisal]

AddOptionsWithValidateOnStart can register the validation but there is one problem in WASM, it can't handles until you resolove the service yourself, you can fxi it using explicity calling host.Services.GetRequiredService<IOptions>() at startup.

sing Microsoft.AspNetCore.Components.WebAssembly.Hosting;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Options;
using ValidateOptions.Client;

var builder = WebAssemblyHostBuilder.CreateDefault(args);

builder.Services
.AddOptionsWithValidateOnStart()
.Bind(builder.Configuration.GetSection("Foo"))
.ValidateDataAnnotations();

var host = builder.Build();

// force the options to resolve & validate here
host.Services.GetRequiredService<IOptions>();

// if invalid, this will throw and prevent app from running

await host.RunAsync();

[philipmorley]

Thanks, it looks like you have to actually call the options to get the validator to fire. I modified your example slightly:

var foo = host.Services.GetRequiredService<IOptions>();
var bar = foo.Value.Bar;

And when I did this I got the 'Unhandled error has occurred...' error to appear on startup. It's a little bit ugly to have that unused bar variable in my startup code, but I can live with this as a workaround.

Thanks for your help.