I don't have an answer for you, but as a primarily front end dev I often get lost there also.

Hi,

The short(ish), not entirely technically correct but hopefully understandable, answer:

There are two basic elements to an MVC site - compiled code and non-compiled "code". Non compiled includes, Views and your front end JS etc - you've found you can happily change this stuff.

As a pure front ender you might be finding code examples which are on the compiled side. This means you can't just drop a .cs file (c#) into the website and it expect it to be picked up (something you might be used to with PHP or similar). It will need to be compiled and forms part of a DLL - this code is picked up when the website starts up. Usually you need to compile, build and release this code.

Here's the good news - you can have code that should really be compiled picked up when the website starts (NOTE: use of this technique should be limited as it can get unwieldy quickly and has MANY downsides!!).

Create a folder in the website directory called App_Code - now if you drop a .cs file in there the website will compile it at startup. This means also if you have some error in your syntax you will also break your website so be careful and don't do this development on a live site!

In fact - if you're getting to this point it's time to start using Visual Studio and building releases, trust me the time in learning this stuff will pay off. This route means that you will be able know on build that you've not broken your site and you'll get lots of hints and tips from Intellisense (think of it as Autocomplete / Autocorrect).

But for now..

• Create a folder in your website called App_Code
• Create a text file titled "CustomFourOhFour.cs"
• Paste the below in.. (I've combined the two files you need from the Umbraco documentation into one for ease).
• Check the site still starts up!
• Create a doctype with the alias fourOhFourPageAlias for each site

This seems to require the Umbraco.Core.Composing class, which doesn't seem to be available in v7.

It seems the example you provided is meant for v8. I am running v7. I did find this example:

https://24days.in/umbraco-cms/2014/the-double-album/multi-site-404/

but I don't know how to combine them like you did. I get that you have to create a icontenthandler and then have to register it.

Thank you so much! I have been looking for this solution for a while. I had to tweak the code a bit to get it to work on my installation, but not much. I marked your post as the answer. Below is the final result.

using System;
using System.Linq;
using System.Globalization;
using Umbraco.Core;
using Umbraco.Core.Models;
using Umbraco.Web;
using Umbraco.Web.Routing;
using System.Web;

namespace FourOhFour
{
    public class MyApplication : ApplicationEventHandler
    {
        protected override void ApplicationStarting(UmbracoApplicationBase umbracoApplication, ApplicationContext applicationContext)
        {
            // Add custom 404 content finder. Use last chance finder so it will return 404 response code correctly...
            ContentLastChanceFinderResolver.Current.SetFinder(new FourOhFourContentFinder());
        }
    }

    public class FourOhFourContentFinder : IContentFinder
    {
        public bool TryFindContent(PublishedContentRequest contentRequest)
        {
        //Get all root sites...
            var allRoots = contentRequest.RoutingContext.UmbracoContext.ContentCache.GetAtRoot();

        //Get current site domain...
            var domain = HttpContext.Current.Request.Url.GetLeftPart(UriPartial.Authority);

        //Get the root node of current site...
            var rootNode = allRoots.Where(f => f.UrlWithDomain().StartsWith(domain)).FirstOrDefault();

            if (rootNode != null)
            {
                //Get the site's specific 404 page.  Must be called '404 Error Page'...
        IPublishedContent notFoundNode = rootNode.Descendants().Where(x => x.Name == "404 Error Page").FirstOrDefault();

                if (notFoundNode != null)
                {
                    contentRequest.PublishedContent = notFoundNode;
                } else {
            //If nothing is found, put in the main site's 404 page...
            contentRequest.PublishedContent = contentRequest.RoutingContext.UmbracoContext.ContentCache.GetById(6008);
        }
            }

            return contentRequest.PublishedContent != null;
        }
    }
}

Well, it's not working now. It works in my test installation, but not on production. I don't know what is different between the two installs.

What is happening is basically it's acting as if I have added no code. It does nothing. No errors, just the ugly Umbraco 404 page, which is what you get when you don't set a default 404 page in the config.

Does anyone have any ideas? I tried replacing this:

ContentLastChanceFinderResolver.Current.SetFinder(new FourOhFourContentFinder()); 

With this:

ContentFinderResolver.Current.InsertTypeBefore<ContentFinderByNotFoundHandlers, FourOhFourContentFinder>();

And nothing changed.

Well, it now seems to be working. I think it was a caching issue. Thanks again to Steve for helping me solve this one!

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