Subscribing To Notifications

Subscribing to notifications allows you to run custom code in response to specific events, such as when the content is created, updated, or deleted. This feature enables you to automate tasks, validate data, log actions, and implement other custom functionalities to enhance your content management system.

To follow this guide, ensure you have an Umbraco installation with content, such as the Umbraco starter kit. In this article, we will walk you through the process of logging a message every time a document is published in Umbraco.

Create a Notification Handler

We will add a string of text to the log whenever a document is published. This log is useful for debugging, as different parts of the Umbraco codebase log key events, warnings, and errors.

1. Add a new C# class file to your project. For example: ~/App_Plugins/Notifications/LogWhenPublishedHandler.cs.

2. Implement the INotificationHandler<ContentPublishedNotification> interface to identify this class as a handler for content publication events.

3. Add the following using statements at the top of your file:

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   using Umbraco.Cms.Core.Events;
   using Umbraco.Cms.Core.Notifications;

Your class should now look like this:

using Umbraco.Cms.Core.Events;
using Umbraco.Cms.Core.Notifications;

namespace MyProject;

public class LogWhenPublishedHandler : INotificationHandler<ContentPublishedNotification>
{
    // Here we will handle a notification.
}

Implement the Handle Method

The INotificationHandler interface requires a Handle method to be implemented.

Use the code snippet below to implement the Handle method, which takes a ContentPublishedNotification parameter. This method will contain the custom logic that runs after content is published.

using Umbraco.Cms.Core.Events;
using Umbraco.Cms.Core.Notifications;

namespace MyProject;

public class LogWhenPublishedHandler : INotificationHandler<ContentPublishedNotification>
{
    public void Handle(ContentPublishedNotification notification)
    {
        // The custom code to fire every time content is published goes here!
        throw new System.NotImplementedException();
    }
}

Inject a Logger for Logging

To log messages, we need to inject a Microsoft ILogger into the handler.

1. Add a using statement for the Microsoft.Extensions.Logging namespace to your file.

2. Add a constructor to the handler class that accepts an ILogger instance.

Your updated class should look like this:

using Microsoft.Extensions.Logging;
using Umbraco.Cms.Core.Events;
using Umbraco.Cms.Core.Notifications;

namespace MyProject;

public class LogWhenPublishedHandler : INotificationHandler<ContentPublishedNotification>
{
    private readonly ILogger<LogWhenPublishedHandler> _logger;

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

        public void Handle(ContentPublishedNotification notification)
        {
            // The custom code to fire every time content is published goes here!
            throw new System.NotImplementedException();
        }
}

Log the Content Publication

Now that we have a logger, let us use it to log a message every time content is published.

Use the code snippet below to replace the NotImplementedException with the code that logs the publication event.

public void Handle(ContentPublishedNotification notification)
{
    // The custom code to fire every time content is published goes here!
    _logger.LogInformation("Something has been published.");
    foreach (var publishedItem in notification.PublishedEntities)
    {
        _logger.LogInformation("{ContentName} was published", publishedItem.Name);
    }
}

using Microsoft.Extensions.Logging;
using Umbraco.Cms.Core.Events;
using Umbraco.Cms.Core.Notifications;

namespace MyProject;

public class LogWhenPublishedHandler : INotificationHandler<ContentPublishedNotification>
{
    private readonly ILogger<LogWhenPublishedHandler> _logger;
            
        public LogWhenPublishedHandler(ILogger<LogWhenPublishedHandler> logger)
        {
            _logger = logger;
        }

        public void Handle(ContentPublishedNotification notification)
        {
            _logger.LogInformation("{ContentName} was published", publishedItem.Name);
        }
}

Register the Notification Handler

Umbraco needs to know that our handler exists and that it handles ContentPublishedNotification. We need to register it in the Program.cs file.

1. Open the Program.cs file at the root of the project.

2. Add the using Umbraco.Cms.Core.Notifications; statement.

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   using Umbraco.Cms.Core.Notifications;

3. Register the handler in the builder configuration by adding the .AddNotificationHandler<ContentPublishedNotification, LogWhenPublishedHandler>() method call.

   The registration should look like this:

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   builder.CreateUmbracoBuilder()
       .AddBackOffice()
       .AddWebsite()
       .AddDeliveryApi()
       .AddComposers()
       .AddNotificationHandler<ContentPublishedNotification, LogWhenPublishedHandler>()
       .Build();

Publishing Content and Verifying Custom Log Messages

1. Access the Umbraco backoffice and publish a piece of content.

2. Check the log messages in the Log Viewer under the Settings section.
3. Search All Logs.

If everything is set up correctly you will see your custom log messages.

Additional Notes

• The code in this article logs a message after content is published because we subscribed to ContentPublishedNotification.

• If you need to run code before content is published, you can subscribe to ContentPublishingNotification instead.

• This pattern applies to other events as well, such as Saving, Saved, Copying, Copied and so on.

More Information

• For further details on Notifications in Umbraco, see the Using Notifications article.