Inversion of Control / Dependency injection

Inversion of Control/Dependency Injection in Umbraco

Umbraco supports dependency injection out of the box using the ASP.NET Core built-in dependency injection. This means that working with dependencies in Umbraco is similar to working with them in ASP.NET Core.

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 accessors, and so on. You can access the IServiceCollection directly to add custom services through the Services property. See below for a concrete example:

IUmbracoBuilder.Services

Registering dependencies

There are different strategies for registering your dependencies and not one strategy is better than the other.

In this article, we will cover the following three strategies:

• Registering dependencies in the Program.cs file

• Registering dependencies in a composer

• Registering dependencies in bundles

Which strategy to choose depends on the scenario requiring dependency registration.

Choosing a strategy for registering dependencies

Are you working directly on your site? You can choose whichever strategy you prefer working with.

Are you building a package and do not have access to the Program.cs file? In this case, you have the option to register the dependencies in a composer.

Are you in a situation where you need to register more than a few dependencies? You can bundle your dependencies in custom extension methods and register them in a single call.

Registering dependencies in the Program.cs file

When working with your Umbraco site, dependencies can be registered within the Program.cs file.

In the example below, a custom notification handler is added to the CreateUmbracoBuilder() builder chain:

Program.cs

builder.CreateUmbracoBuilder()
    .AddBackOffice()
    .AddWebsite()
    .AddDeliveryApi()
    .AddComposers()
    // When you need to add something Umbraco-specific, do it in the "AddUmbraco" builder chain, using the IUmbracoBuilder extension methods.
    .AddNotificationHandler<ContentTypeSavedNotification, ContentTypeSavedHandler>()
    .Build();

Learn more about the uses of the Program.cs file in the official ASP.NET Core Fundamentals documentation.

Registering dependencies in a composer

When working with packages, you do not have access to the Program.cs file. Instead, you can use a composer to register your dependencies.

Below is an example of a composer using the Services property of the IUmbracoBuilder:

MyComposer.cs

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>();
    }
}

To access the IUmbracoBuilder, you need to add Umbraco.Cms.Core.DependencyInjection and Microsoft.Extensions.DependencyInjection as using statements when registering your services. This, in turn, will also give you access to the IUmbracoBuilder extension methods as well as the Microsoft IServiceProvider.

Registering dependencies in bundles

Depending on your scenario, you may have a lot of dependencies you need to register. In this case, your Program.cs or Composer can become cluttered and hard to manage.

You can manage multiple services in one place by creating your custom extension methods for the IUmbracoBuilder. This way you can bundle similar dependencies in extension methods and register them all in a single call.

In the following code sample two dependencies, RegisterCustomNotificationHandlers and RegisterCustomServices are bundled together in a custom AddCustomServices extension method.

MyCustomBuilderExtensions.cs

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
{
    // The first dependency is registered
    public static IUmbracoBuilder RegisterCustomNotificationHandlers(this IUmbracoBuilder builder)
    {
        builder.AddNotificationHandler<ContentTypeSavedNotification, ContentTypeSavedHandler>();
        {...}
        return builder;
    }

    // The second dependency is registered
    public static IUmbracoBuilder RegisterCustomServices(this IUmbracoBuilder builder)
    {
        builder.Services.AddSingleton<IFooBar, Foobar>();
        {...}
        return builder;
    }

    // The two dependencies are bundled together
    public static IUmbracoBuilder AddCustomServices(this IUmbracoBuilder builder)
    {
        builder.RegisterCustomNotificationHandlers();
        builder.RegisterCustomServices();
        return builder;
    }
}

It is not required to have an interface registering your dependencies:

services.AddSingleton<Foobar>();

With the dependencies bundled together, you can call the AddCustomServices method in either the Program.cs file or your composer:

Program.cs

Program.cs

builder.CreateUmbracoBuilder()
    .AddBackOffice()
    .AddWebsite()
    .AddDeliveryApi()
    .AddComposers()
    // Register all custom dependencies in one go using the custom extension method
    .AddCustomServices()
    .Build();

Composer

MyComposer.cs

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

namespace IOCDocs;

public class MyComposer : IComposer
{
    public void Compose(IUmbracoBuilder builder)
    {
        // Register all custom dependencies in one go using the custom extension method
        builder.AddCustomServices();
    }
}

Service lifetime

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

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

There are three possible lifetimes:

Name	Lifetime	Description
Transient	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 of at the end of the request. Be careful not to resolve a scoped service from a singleton, as it may lead to 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, read the official Microsoft documentation on dependency injections.

Injecting dependencies

Once you have registered the dependencies inject them into your project where needed.

Injecting dependencies into a class

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

The example below uses UmbracoApiController which is obsolete in Umbraco 14 and will be removed in Umbraco 15.

FooController.cs

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. This is what you would expect as all the Foobar.Foo() method does is to return Bar as a string:

Foobar.cs

namespace IOCDocs.Services;

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

Injecting dependencies into a View or Template

In some cases you might need to use services within your templates or view files. Services can be injected directly into your views using the @inject keyword. This means that you can inject the Foobar from above into a view like shown below:

Home.cshtml

@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 statement for the namespace of the service *@
@using IOCDocs.Services
@* Inject the service *@
@inject IFooBar _fooBar

@{
 Layout = null;
}

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

When loading a page using the template above, you will see the "Bar" heading which is retrieved from the service.

To use the service a using statement for the namespace of the service needs to be added.

Other things you can inject

In this section, you can find examples of what you can inject when working with Umbraco.

UmbracoHelper

Read more about the UmbracoHelper

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

MyCustomScopedService.cs

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;
        }

        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();
        }
    }
}

Using the UmbracoHelper is only possible when there is an instance of the UmbracoContext. You can read more in the implementation article about services.

ExamineManager

Read more about the ExamineManager in the Searching articles.

SearchService.cs

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))
        {
            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);
        }
        
        // 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 in the debugging section

Foobar.cs

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

In the Services and Helpers documentation, you can find more examples of using dependency injection and gaining access to the different services and helpers.

You will also find information about creating custom services and helpers to inject and use in your Umbraco project.