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I'm not sure if this is achievable at present, but I'm trying to create a UserActivity in my Xamarin Forms (Android) app that will be published to the Microsoft Graph. There doesn't seem to be much guidance on how to use the Microsoft Graph .NET SDK and I'm struggling to get this working. The ideal solution would be to publish a UserActivity after visiting a page in Xamarin Forms, and then make this available on Timeline, so the app could be launched again on Android through Microsoft Launcher or Windows Timeline.

So far, I've integrated the authentication flow into the app, and given the required permissions. I've had a go at the coding and this is what I've done so far:

 public UserActivity CreateUserActivity(string appActivityId)
 
 var activity = new UserActivity()
 
 AppActivityId = appActivityId,
 ActivitySourceHost = "https://graphexplorer.blob.core.windows.net",
 AppDisplayName = "My App",
 ActivationUrl = "https://developer.microsoft.com/en-us/graph/graph-explorer",
 FallbackUrl = "https://developer.microsoft.com/en-us/graph/graph-explorer",
 VisualElements = new VisualInfo()
 
 Description = "A user activity made through the Graph .NET SDK tests",
 BackgroundColor = "#008272",
 DisplayText = "Graph .NET SDK Test User Activity",
 Attribution = new ImageInfo()
 
 IconUrl = "https://graphexplorer.blob.core.windows.net/explorerIcon.png",
 AlternateText = "Microsoft .NET SDK",
 AddImageQuery = false,
 ,
 ,
 ;
 return activity;
 

 private async void TrialButton_Clicked(object sender, EventArgs e)
 
 await graphClient.Me.Activities.Request().AddUserActivityAsync(CreateUserActivity("hello"));
 

While I realise I've not set my own ActivitySourceHost, etc. I keep getting the following error:

System.NullReferenceException: Object reference not set to an instance of an object.

when calling AddUserActivityAsync, so I'm not sure if I have the basic code correct for creating and publishing the UserActivity. Any help would be much appreciated.