user control use in sitefinity and button submit time dropdown is reset with empty

Refrence: https://docs.telerik.com/devtools/aspnet-ajax/controls/ajaxmanager/how-to/load-user-controls

protected void Page_Load(object sender, EventArgs e)
        {
            //-----pramod
            if (this.CurrentControl != string.Empty)
            {
                LoadMyUserControl(CurrentControl, this.Page);
            }
}


protected void Page_Init(object sender, EventArgs e)
        {
           FunBindCategory();
        }

    private string CurrentControl
        {
            get
            {
                return this.ViewState["CurrentControl"] == null ? string.Empty : (string)this.ViewState["CurrentControl"];
            }
            set
            {
                this.ViewState["CurrentControl"] = value;
            }
        }
        private void LoadMyUserControl(string controlName, Control parent)
        {
            parent.Controls.Clear();
            UserControl MyControl = (UserControl)LoadControl(controlName);
            string userControlID = controlName.Split('.')[0];
            MyControl.ID = userControlID.Replace("/", "").Replace("~", "");
            parent.Controls.Add(MyControl);
            this.CurrentControl = controlName;
        }

protected void btnSubmit_Click(object sender, EventArgs e)
        {
           
                this.LoadMyUserControl("~/UserControls/BackendModule/SchemeCategory Master/ucSchemeCategory.ascx", this.Page);
string test= drpcategory.SelectedValue;

}