An error occurred while creating a route

Question

I try to add an area to my .NET Core project, but always I see that error:

RouteCreationException: An error occurred while creating the route with name '(My Area Name)'

My Code is :

public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
    if (env.IsDevelopment())
    {
        app.UseBrowserLink();
        app.UseDeveloperExceptionPage();
        app.UseDatabaseErrorPage();
    }
    else
    {
        app.UseExceptionHandler("/Home/Error");
    }

    app.UseStaticFiles();

    app.UseAuthentication();

    app.UseMvc(routes =>
    {
        routes.MapRoute(
            name: "default",
            template: "{controller=Home}/{action=Index}/{id?}");

        routes.MapRoute(
            name: "custom",
            template: "{area:my area name}/{{controller=AdminHome}/{action=Index}/{id?}");
    });
}

And in configure services I add this code:

public void ConfigureServices(IServiceCollection services)
{
    //...

    services.AddRouting(); 

    //...
}

And in controller I added:

[Area("My Area Name")]
public class AdminHomeController : Controller
{
    public IActionResult Index()
    {
        return View();
    }
}

The error is :

RouteCreationException: An error occurred while creating the route with name 'custom' and template '{area:area name}/{{controller=Home}/{action=Index}/{id?}'. \r\n Microsoft.AspNetCore.Routing.RouteBase..ctor(string template, string name, IInlineConstraintResolver constraintResolver, RouteValueDictionary defaults, IDictionary constraints, RouteValueDictionary dataTokens) \r\n ArgumentException: There is an incomplete parameter in the route template. Check that each '{' character has a matching '}' character. \r\n Parameter name: routeTemplate

Answer 1

As stated in the error message, you have a stray { in the route template that is making it invalid

template: "{area:my area name}/{{controller=AdminHome}/{action=Index}/{id?}");
                               ^
                               |
                             here

You also need to rearrange the order of routes to avoid route conflicts.

app.UseMvc(routes => {
    routes.MapRoute(
        name: "custom",
        template: "{area:my area name}/{controller=AdminHome}/{action=Index}/{id?}");

    routes.MapRoute(
        name: "default",
        template: "{controller=Home}/{action=Index}/{id?}");
});

Reference Areas in ASP.NET Core

Answer 2

I am using .Net Core 3.1 Web API project, the problem was in the controller where we specify the route at the the top of the controller, Below is snippet of what was wrong and then what was correct :

ERROR

[Route("api/users/{userId/photos")]

I was missing the closing "}" after userId, which caused this issue.

WORKING

[Route("api/users/{userId}/photos")]

Hope it helps others :)

Answer 3

Lot of times you make several changes to many files and then you are searching in the Statup.cs in .net core only to end up realizing you messed up an attribute on a new web api method like this

[HttpGet("{id:int")]  

Answer 4

routes.MapRoute(
    name: "default",
    template: "{controller}/{action}/{id?}",
    defaults: new { controller = "Home", action = "Index", id = "id?" } 
);
routes.MapRoute(
    name: "persianredditacp",
    template: "{area}/{controller}/{action}/{id?}"
);  

THAT worked!