SharePoint Online Provider Hosted App Context Token Is NULL On Postback

Question

I have a provider hosted app in SharePoint Online. The problem I have is sometimes on postback the TokenHelper Class method GetContextTokenFromRequest is returning Context Token as NULL

  ContextToken = TokenHelper.GetContextTokenFromRequest(Page.Request);

Answer 1

I got the issue resolved by using view state for the Context Token property

 public string ContextToken
       {
            get
           {
            return ViewState["ContextToken"] != null ? Convert.ToString(ViewState["ContextToken"]) : String.Empty;
        }
        set 
        {
            if (value != null)
            {
                ViewState["ContextToken"] = value;
            }
        }
    }