UserControl value is not changed when written thru code behind

i have one user control which has hiddenField name ='hdnShow' as runat='server'
my scenario is that i have a function in userControl name Show(MessageType); 
void Show(MessageType msg)
{
switch(msg)
        {
            case MessageType.Success:hdnShow.Value= "Success fully saved";
                break;
            case MessageType.Fail: hdnShow.Value= "Failed";
                break;

            case MessageType.Update: hdnShow.Value = "Success fully updated";
          &n ...