How to access localhost from Android emulator and iOS simulator?

Being lucky to develop a backend and a Xamarin.Forms clients on your own? Sooner or later you will have to debug the API calls and it might become painful. Unless, you will follow the next rules:

  1. Configure your API URL to run on 127.0.0.1 instead of a localhost:

    // .NET Core Web.Api example
    public static IWebHost BuildWebHost(string[] args) =>
    WebHost.CreateDefaultBuilder(args)
    .UseStartup<Startup>()
    .UseUrls(“http://127.0.0.1:5001“)
    .Build();

  2. Configure your Xamarin.Forms API consumer to have a conditional URL base:

    string apiUrl = null;
    if (Device.RuntimePlatform == Device.Android)
    apiUrl = “http://10.0.2.2:5001/api“;
    else if (Device.RuntimePlatform == Device.iOS)
    apiUrl = “http://localhost:5001/api“;
    else
    throw new UnsupportedPlatformException();

The problem with Android emulator is that it maps 10.0.2.2 to 127.0.0.1, not to localhost. However, the iOS Simulator uses the host machine network.

That should be it!
Happy debugging!

Web.API 2 centralised model state validation

Model state validation is easy with DataAnnotations. However, you will find repeating the next line of code very soon:


if(!ModelState.IsValid) return BadRequest(..);

Luckily, there is a pretty simple solution – to use ActionFilter:

using System;
using System.Net;
using System.Net.Http;
using System.Web.Http.Controllers;
using System.Web.Http.Filters;
namespace MyAwesomeWebApi.ActionFilters
{
/// <summary>
/// Returns 400 if the ModelState is invalid.
/// </summary>
[AttributeUsage(AttributeTargets.All, AllowMultiple = false, Inherited = true)]
public class ValidateModelAttribute : ActionFilterAttribute
{
public override void OnActionExecuting(HttpActionContext actionContext)
{
if (actionContext.ModelState.IsValid)
return;
actionContext.Response = actionContext.Request.CreateErrorResponse(HttpStatusCode.BadRequest, actionContext.ModelState);
}
}
}
using System.Collections.Generic;
using System.Threading.Tasks;
using System.Web.Http;
using System.Web.Http.Description;
using System.ComponentModel.DataAnnotations;
namespace MyAwesomeWebApi.Controllers
{
public class ValuesController : ApiController
{
[ValidateModel]
public IHttpActionResult Post(MyModel model)
{
var valService = new ValService();
var result = valService.Create(model);
return Created($"api/values/{result.Id}", result);
}
}
public class MyModel
{
[Required]
public int Id { get; set; }
}
}
view raw ValuesController.cs hosted with ❤ by GitHub

All you have to do is to add the ValidateModel attribute to your controller methods that require model state validation.