Getting "The property or field 'DefaultDisplayFormUrl' has not been initialized." Exception

Question

Here I want to create a URL of a Event(s) of sharepoint calendar list in c#. For that I am using the DefaultDisplayFormUrl as per my below code.

foreach (SPListItem item in listItems)
{
    DateTime startDate = DateTime.Parse(item[StartDateField].ToString().Trim());
    string fullUrl = "";
    var itemId = "?ID=" + item.ID;
    if (item[RecurrenceField].ToString() == "True")
    {
        string eventURL = "0";
        if ((int)item[EventTypeField] == 4)
        {
            eventURL = ".1." + item[SeriesIdField];
        }
        else
        {
            SPRegionalSettings oRegionalSettings = web.RegionalSettings;
            SPTimeZone oTimeZone = oRegionalSettings.TimeZone;
            int dtHour = startDate.Hour;
            int dtMinute = startDate.Minute;
            int dtSecond = startDate.Second;
            bool isAllDayEvent = Convert.ToBoolean(item["fAllDayEvent"]);
            if (isAllDayEvent)
            {
                dtHour = 0;
                dtMinute = 0;
                dtSecond = 0;
            }
            var dtDateNew = new DateTime(startDate.Year, startDate.Month, startDate.Day,
                dtHour, dtMinute, dtSecond);
            DateTime utcDate = oTimeZone.LocalTimeToUTC(dtDateNew);

            if (isAllDayEvent)
            {
                utcDate = dtDateNew;
            }
            eventURL = ".0." + String.Format(
                "{0:yyyy-MM-ddTHH:mm:ssZ}",
                utcDate);
        }
        fullUrl =
            item.ParentList.ParentWeb.Site.MakeFullUrl(item.ParentList.DefaultDisplayFormUrl +
                                                       itemId + eventURL + "&Source=" + returnUrl);
    }
    else
    {
        fullUrl =
            item.ParentList.ParentWeb.Site.MakeFullUrl(item.ParentList.DefaultDisplayFormUrl +
                                                       itemId + "&Source=" + returnUrl);
    }
}

bet here I am getting the exception which is not allowing me create the complete URL. can anyone help with this?