为什么我必须在ASP 5中的app.UseMvc之前调用app.UseErrorHandler才能使用它？

Question

I created an ASP.NET 5 application for Web API and installed Asp.Net.Diagnostics from NuGet so I could add my own error handling.

What works: (From Configuration function in Startup.cs)

app.UseErrorHandler("/Home/Error");
app.UseMvc(routes => {
    routes.MapRoute("Default", "{controller=Home}/{action=Index}/{id?}");
});

What doesn't work: (app uses normal error handler instead of the custom one)

app.UseMvc(/*..configure routes..*/);
app.UseErrorHandler("/Home/Error");

Inside my controller I'm throwing:

throw new NotImplementedException("This method is not implemented");

I usually configure my big things first and the details later in case the details get overwritten. In this case, though, I need to configure my big thing (MVC) after my smaller thing (ErrorHandler), or my ErrorHandler doesn't work. Why is that?

Answer 1

Because route order in ASP.NET is important. Configuring big things first and details later is not what the system is expecting.

ASP.NET checks the first route. If it matches, then it doesn't check the rest of the routes.

For further details, see this blog post I found. It's for an older version of ASP.NET, but I believe the principles still apply.