MapSpaFallbackRoute on Startup ASP .NET Core - asp.net-core

Question

I have an Areas on Net Core App named Admin, on MapSpaFallbackRoute setting on startup, I want to set like this,
app.UseMvc(routes =>
{
routes.MapSpaFallbackRoute(
name: "spa-fallback-admin",
defaults: new { area="Admin", controller = "Home", action = "Index" });
});
is this the correct way to define MapSpaFallbackRoute? I doubt MapSpaFallbackRoute have attributes area,
I have been try this, and my apps return 404(not found).
so, what the correct way to define MapSpaFallbackRoute, I want using HomeController on Admin area, with Index action
It is my complete code, I want to request with path admin, controller on admin areas should be handle that.
app.MapWhen(context => context.Request.Path.Value.StartsWith("/admin"), builder =>
{
builder.UseMvc(routes =>
{
routes.MapRoute(
name: "default",
template: "{area=Admin}/{controller=Home}/{action=Index}/{id?}");
routes.MapSpaFallbackRoute(
name: "spa-fallback-admin",
defaults: new { area="Admin", controller = "Home", action = "Index" });
});
});
app.UseMvc(routes =>
{
routes.MapRoute(
name: "default",
template: "{controller=Home}/{action=Index}/{id?}");
routes.MapSpaFallbackRoute(
name: "spa-fallback",
defaults: new { controller = "Home", action = "Index" });
routes.MapRoute(
name: "areas",
template: "{area:exists}/{controller=Home}/{action=Index}/{id?}");
});
thanks for your help

Answer 1

What MapSpaFallbackRoute does is allows defining default values for route parameters to handle 404 cases.
Now to your question: yes, MVC routing (both attribute/convention) supports {area} as route parameter and so you can write above code to define a default value.
You didn't show your routing setup, so I assume that your main problem is that you haven't specified {area} parameter in your route template.
For example, if consider convention routing, the following should work:
app.UseMvc(routes => {
routes.MapRoute("default", "{area}/{controller}/{action}/{id?}");
routes.MapSpaFallbackRoute(
name: "spa-fallback-admin",
defaults: new { area="Admin", controller = "Home", action = "Index" });
});
For updated question:
Try to use .UseWhen instead of .MapWhen:
app.UseWhen(context => context.Request.Path.Value.StartsWith("/admin"), builder =>
{

Answer 2

after searching for this issue I realize Dotnet core 3 doesn't support MapSpaFallbackRoute method so to fix this problem you should add the Spa package manually use this command on your terminal Dotnet
add package Microsoft.AspNetCore.SpaServices --version 3.1.16
you can check the version at this link
NuGet Gallery