unable to get the emails from outlook by using graph api - getting NullReferenceException: Object reference not set to an instance of an object error

Question

unable to get the emails from outlook by using graph api get method

    public List<Message> GetAllMails()
    {
        List<Message> mails = new List<Message>();
        //var result = graphClientV1.Me.Messages.Request().GetAsync();
        //IUserMessagesCollectionPage currentPage = result.Result;
        IUserMessagesCollectionPage currentPage = graphClientV1.Me.Messages.Request().GetAsync().Result;
        while (currentPage != null)
        {
            foreach (var mail in currentPage)
            {
                try
                {
                    mails.Add(mail);
                }
                catch (Exception) { }
            }
            currentPage = (currentPage.NextPageRequest != null) ? currentPage.NextPageRequest.GetAsync().Result : null;
        }
        return mails;
    }

i want to get the all mails from outlook.

error:

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

Answer 1

Default paging in the Graph is only 10 in email so if your trying to get all emails in a folder using that would be quite slow due to the number of requests you may need to make (if there are a large number of items in the folder) and your likelihood of getting throttled would be high also.

The Graph SDK has a PageIterator class so its best to use that, restrict the properties to just what you need and set the page size to up to 1000

eg

            var messages = graphServiceClient.Me.Messages
            .Request()
            .Select(e => new {
                e.Sender,
                e.Subject,
            })
            .Top(1000)
            .GetAsync().GetAwaiter().GetResult();

        var pageIterator = PageIterator<Message>
            .CreatePageIterator(
                graphServiceClient,
                messages,
                // Callback executed for each item in  
                // the collection  
                (m) =>
                {
                    Console.WriteLine(m.Subject);
                    return true;
                }
            );

        pageIterator.IterateAsync().GetAwaiter().GetResult();

You also might want to consider using the latest Kiota based version of the Graph SDK.