Remote Event Receivers are a powerful way to integrate custom code into your SharePoint Online environment. Essentially a Remote Event Receiver is a hook that allows you to execute your code in response to an event that occurs in SharePoint. There are several techniques for responding to events in SharePoint Online, but the Remote Event Receiver is the most powerful. It offers dozens of different events to attach to and allows you to configure synchronously or asynchronously. It is also very easy to attach, develop, deploy, test, and maintain. Is also very misunderstood.
Remote Event Receivers were introduced along with SharePoint 2013 and the arrival of the App model. Microsoft provided tooling with Visual Studio to create Remote Event Receivers, but unfortunately the only way to expose this tooling was in the context of a Provider-Hosted App.
This is unfortunate because Remote Event Receivers have nothing to do with Provider-Hosted Apps. In order to develop a Remote Event Receiver using the Microsoft-provided tooling, a developer had to create a Provider-Hosted App project and deploy their RER along with it. This added a great deal of complexity to the development effort, and made packaging and deployment a painful and tedious experience.
To further complicate things, Microsoft decided to wire up a WCF service as the endpoint in its RER tooling. This is sheer lunacy, even back in 2013. A web API project would have been simpler and would be more in line with Microsoft development tooling efforts. The opacity and complexity of WCF made RER development even more cumbersome. Actually, I believe they decided to use the WCF service so the development experience would be similar to that of old-school Event Receivers, with the ability to use a deserialized Event Properties object.
Building a Remote Event Receiver is Easy
In truth, it is remarkably simple to configure, develop, deploy, and maintain a Remote Event Receiver, but in order to do so you must completely abandon the Microsoft tooling and just set up the pieces yourself. Luckily there are really only two components to a Remote Event Receiver:
- The endpoint
- The registration
The registration is where you tell SharePoint, “call this endpoint every time this event occurs”. The CSOM provides mechanisms for adding Remote Event Receivers, but the details depend somewhat on the type of event receiver being deployed. The PnP PowerShell library provides the ability to register a Remote Event Receiver in a one-liner. For example, to set up an RER that is invoked every time an item is updated on a list, execute:
Add-PnPEventReceiver -List "Tasks" -Name "TasksRER" -Url https://my-rer.azurewebsites.net/Service1.svc -EventReceiverType ItemAdded -Synchronization Asynchronous
The endpoint is just a web service listening at a certain URL, and you have lots of options for this. A Web API project would work great for this. Azure Functions are also a very compelling option. You are also free to write services in Java, Node or whatever other technology you can think of. In the example below, we’ll use the canonical WCF Service you’d get with the Visual Studio item template, but we’re going to sidestep the template and wire things up ourselves. It’s actually easier this way.
Creating the Remote Event Receiver shell
In Visual Studio,
- create an empty ASP.NET web application
- Add the Nuget Package ”AppForSharePointOnlineWebToolkit”.
- Add a new item of type WCF Service to the web app.
- Get rid of the IService reference and set your service to implement IRemoteEventService, which lives in the Microsoft.SharePoint.Client.EventReceivers namespace. This namespace came into the project with the Nuget packages we added earlier. Resolve the squiggly to implement the interface stubs.
Your service class should look something like this:
F5 your project and navigate to the service to make sure it’s accepting requests. Take note of the port number. We’ll need that to set up our proxy for local debugging.
Locally debugging your remote event receiver
To test this event receiver locally, we’ll use ngrok. According to its documentation, “ngrok is a reverse proxy that creates a secure tunnel from a public endpoint to a locally running web service.” We will use it to map an Internet endpoint to our local machine so we can intercept and debug requests coming from SharePoint Online.
Once it connects it’ll output some data, including the public URL of our proxy connection:
Next, open up a browser and navigate to the ngrok URL, append the service endpoint, and you should be able to see that the ngrok URL is returning your service.
Next we’ll attach our event receiver to a SharePoint list. Using the PnP PowerShell cmdlet shown above, we’ll add a Remote Event Receiver to our site. Make sure to open a new PowerShell session for this and leave the ngrok session running in its window. The proxy will be released when the window is closed.
Now, set a breakpoint in your ProcessOneWayEvent method, add a task to the list and make an edit to it. If all goes well your local web service will be called and the breakpoint will hit:
Make sure you closely inspect the properties object in the debugger, and get a feel for all the data that’s in there. For this particular event we’ll want to check out ItemEventProperties and ItemEventProperties.AfterProperties for some useful metadata that gets passed into the service.
Deploying your Remote Event Receiver to Azure
When you are ready to deploy to the Internet you can deploy to Azure just like a normal web application. You’ll want to run Add-PnPEventReceiver using the Internet URL to register your event receiver for real, of course.