Inversion of Control / Dependency injection

Inversion of Control/Dependency Injection in Umbraco

Umbraco v9+ supports dependency injection out of the box. Umbraco uses the ASP.NET Core built-in dependency injection. This means that you don't have to install external packages to register and use your dependencies. If you're familiar with ASP.NET Core, the experience will be similar.

IUmbracoBuilder is a Umbraco-specific abstraction on top of the IServiceCollection, its purpose is to aid in adding and replacing Umbraco-specific services, such as notification handlers, filesystems, server role accessor, and so on. You can access the IServiceCollection directly to add your custom services through the Services property, see below for a concrete example:

IUmbracoBuilder.Services

Registering dependencies

There are two strategies for registering your own dependencies to the container, which one you should use depends on whether you're making a package, or making custom services for your own site.

Registering dependencies for your site

When working with your site, and not a package, the recommended way to register dependencies is with the ConfigureServices method of the Startup class in Startup.cs:

public void ConfigureServices(IServiceCollection services)
{
    services.AddUmbraco(_env, _config)
        .AddBackOffice()
        .AddWebsite()
        .AddComposers()
        // If you need to add something Umbraco specific, do it in the "AddUmbraco" builder chain, using the IUmbracoBuilder extension methods.
        .AddNotificationHandler<ContentTypeSavedNotification, ContentTypeSavedHandler>()
        .Build();

    // Regular services can be added outside the "AddUmbraco" builder chain, using the default IServiceCollection.
    services.AddSingleton<IFooBar, Foobar>();
}

Registering dependencies in packages

When working with packages, you won't have access to the Startup.cs file, so instead you must use a composer to register your own dependencies in the container, using the Services property, or appropriate extension method, of the IUmbracoBuilder:

using IOCDocs.NotificationHandlers;
using IOCDocs.Services;
using Microsoft.Extensions.DependencyInjection;
using Umbraco.Cms.Core.Composing;
using Umbraco.Cms.Core.DependencyInjection;
using Umbraco.Cms.Core.Notifications;

namespace IOCDocs
{
    public class MyComposer : IComposer
    {
        public void Compose(IUmbracoBuilder builder)
        {
            builder.AddNotificationHandler<ContentTypeSavedNotification, ContentTypeSavedHandler>();
            builder.Services.AddSingleton<IFooBar, Foobar>();
        }
    }
}

Remember to add Umbraco.Cms.Core.DependencyInjection and Microsoft.Extensions.DependencyInjection as 'using' statements where you register your services, to gain access to the IUmbracoBuilder, its extension methods, and the Microsoft `IServiceProvider.

Builder extension methods

Depending on your scenario, you may have a lot of dependencies you need to register, in this case, your Startup.cs or Composer might become cluttered and hard to manage. A great way to manage multiple services is by creating your own custom extension methods for the IUmbracoBuilder, this way you can group similar dependencies in extension methods and register them all in as little as a single call:

using IOCDocs.NotificationHandlers;
using IOCDocs.Services;
using Microsoft.Extensions.DependencyInjection;
using Umbraco.Cms.Core.DependencyInjection;
using Umbraco.Cms.Core.Notifications;

namespace IOCDocs
{
    public static class MyCustomBuilderExtensions
    {
        public static IUmbracoBuilder RegisterCustomNotificationHandlers(this IUmbracoBuilder builder)
        {
            builder.AddNotificationHandler<ContentTypeSavedNotification, ContentTypeSavedHandler>();
            {...}
            return builder;
        }

        public static IUmbracoBuilder RegisterCustomServices(this IUmbracoBuilder builder)
        {
            builder.Services.AddSingleton<IFooBar, Foobar>();
            {...}
            return builder;
        }

        public static IUmbracoBuilder AddCustomServices(this IUmbracoBuilder builder)
        {
            builder.RegisterCustomNotificationHandlers();
            builder.RegisterCustomServices();
            return builder;
        }
    }
}

It is not required to have an interface for your dependency:

services.AddSingleton<Foobar>();

Now you can call your AddCustomServices in either the Startup.cs file, or your composer like so:

public void ConfigureServices(IServiceCollection services)
{
    services.AddUmbraco(_env, _config)
        .AddBackOffice()
        .AddWebsite()
        .AddComposers()
        // Register all our custom services in one go.
        .AddCustomServices()
        .Build();
}

using Umbraco.Cms.Core.Composing;
using Umbraco.Cms.Core.DependencyInjection;

namespace IOCDocs
{
    public class MyComposer : IComposer
    {
        public void Compose(IUmbracoBuilder builder)
        {
            // Register all our custom services in one go.
            builder.AddCustomServices();
        }
    }
}

Service lifetime

During registration you have to define the lifetime of your service:

IServiceCollection.AddTransient<TService, TImplementing>();
IServiceCollection.AddScoped<TService, TImplementing>();
IServiceCollection.AddSingleton<TService, TImplementing>();

There is three possible lifetimes:

• Transient - always creates a new instance

  • A new instance will be created each time it's injected.

• Scoped - one unique instance per web request (connection)

  • Scoped services are disposed at the end of the request

  • Be very careful not to resolve a scoped service from a singleton, since it may cause it to have an incorrect state in subsequent requests.

• Singleton - one unique instance for the whole web application

  • The single instance will be shared across all web requests.

For more information, have a look at the official Microsoft documentation.

Injecting dependencies

Once you have registered your services, factories, helpers or whatever you need for you application, you can go ahead and inject them where needed.

Injecting dependencies into a class

If you need to inject your service into a controller, or another service, you'll do so through the class

using IOCDocs.Services;
using Umbraco.Cms.Web.Common.Controllers;

namespace IOCDocs.Controllers
{
    public class FooController : UmbracoApiController
    {
        private readonly IFooBar _fooBar;

        public FooController(IFooBar fooBar)
        {
            _fooBar = fooBar;
        }

        public string Foo()
        {
            var bar = _fooBar.Foo();
            return bar;
        }
    }
}

If you place a breakpoint on var bar = _foobar.Foo(), open /Umbraco/Api/foo/foo in your browser and inspect the variable, you'll see that the value is bar, which is what you'd expect since all the Foobar.Foo() method does it to return Bar as a string:

namespace IOCDocs.Services
{
    public class Foobar : IFooBar
    {
        public string Foo() => "Bar";
    }
}

Injecting dependencies into a View or Template

You might need to use services within your templates or views, fortunately, you can inject services directly into your views using the @inject keyword. You can for example inject the Foobar from above into a view like so:

@using Umbraco.Cms.Web.Common.PublishedModels;
@inherits Umbraco.Cms.Web.Common.Views.UmbracoViewPage<ContentModels.Home>
@using ContentModels = Umbraco.Cms.Web.Common.PublishedModels;

@* Add a using for the namespace of the service *@
@using IOCDocs.Services
@* Now you can inject it *@
@inject IFooBar _fooBar

@{
	Layout = null;
}

<h1>@_fooBar.Foo()</h1>

If you then load the page which uses this template you'll see a heading with "Bar", which we got from our service.

Note that in order to use our service we also have to add a using statement for the namespace of the service.

Other things you can inject

Most of (if not all) the Umbraco goodies you work with every day can be injected. Here are some examples.

UmbracoHelper

Read more about the UmbracoHelper

UmbracoHelper is a scoped service, therefore you can only use it in services that are also scoped, or transient. To get UmbracoHelper you must inject IUmbracoHelperAccessor and use that to resolve it:

using System.Collections.Generic;
using Umbraco.Cms.Core.Models.PublishedContent;
using Umbraco.Cms.Web.Common;

namespace IOCDocs.Services
{
    // This service must be scoped
    public class MyCustomScopedService
    {
        private readonly IUmbracoHelperAccessor _umbracoHelperAccessor;

        public MyCustomScopedService(IUmbracoHelperAccessor umbracoHelperAccessor)
        {
            _umbracoHelperAccessor = umbracoHelperAccessor;
        }
        
        public IEnumerable<IPublishedContent> GetContentAtRoot()
        {
            // Try and get the Umbraco helper
            var success = _umbracoHelperAccessor.TryGetUmbracoHelper(out var umbracoHelper);
            if (success is false)
            {
                // Failed to get UmbracoHelper, probably because it was accessed outside of a scoped/transient service.
                return null;
            }
            
            // We got Umbraco helper, now we can do something with it.
            return umbracoHelper.ContentAtRoot();
        }
    }
}

The use of the UmbracoHelper is only possible when there's an instance of the UmbracoContext. You can read more here.

ExamineManager

Read more about examine.

using System;
using System.Collections.Generic;
using Examine;
using Umbraco.Cms.Core;
using Umbraco.Cms.Core.Models.PublishedContent;
using Umbraco.Cms.Core.Web;
using Umbraco.Cms.Infrastructure.Examine;
using Umbraco.Extensions;

namespace IOCDocs.Services
{
    // This service must be scoped.
    public class SearchService : ISearchService
    {
        private readonly IExamineManager _examineManager;
        private readonly IUmbracoContextAccessor _umbracoContextAccessor;

        public SearchService(IExamineManager examineManager, IUmbracoContextAccessor umbracoContextAccessor)
        {
            _examineManager = examineManager;
            _umbracoContextAccessor = umbracoContextAccessor;
        }

        public IEnumerable<PublishedSearchResult> Search(string searchTerm)
        {
            if (_examineManager.TryGetIndex(Constants.UmbracoIndexes.ExternalIndexName, out var index) is false)
            {
                throw new InvalidOperationException($"No index found by name {Constants.UmbracoIndexes.ExternalIndexName}");
            }

            if (!(index is IUmbracoIndex umbracoIndex))
            {
                throw new InvalidOperationException("Could not cast");
            }
            
            // Do stuff with the index
            if (_umbracoContextAccessor.TryGetUmbracoContext(out var umbracoContext) is false)
            {
                throw new InvalidOperationException("Could not get Umbraco context");
            }

            return umbracoIndex.Searcher.Search(searchTerm).ToPublishedSearchResults(umbracoContext.PublishedSnapshot.Content);
        }
    }
}

ILogger

Read more about logging

using System;
using Microsoft.Extensions.Logging;

namespace IOCDocs.Services
{
    public class Foobar : IFooBar
    {
        private readonly ILogger<Foobar> _logger;

        public Foobar(ILogger<Foobar> logger)
        {
            _logger = logger;
        }

        public void Foo()
        {
            _logger.LogInformation("Method Foo called at {DateTime}", DateTime.UtcNow);
        }
    }
}

Using DI in Services and Helpers

Services and Helpers - For more examples of using DI and gaining access to Services and Helpers, and creating your own custom Services and Helpers to inject.