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 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 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;
        }

        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))
        {
            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

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.