protected void BindData()
{
string strFirstName = "";
string strLastName="";
DateTime? dtStartDate = null;
DateTime? dtEndDate = null;
var PatientEvaluations = objPatient.GetAllPatientEvaluation(strFirstName,strLastName,dtStartDate.ToString("dd/MM/yyyy"),dtEndDate.ToString("dd/MM/yyyy")).AsQueryable();
GridViewPatient.DataSource = PatientEvaluations;
GridViewPatient.DataBind();
}
You try this, hope it will give expected result what you needed.