Handle control focus while use tab

Hi friends ,

I have resolved myself in above question. I that case , the postback is occurred in some cases. This is the only reason my TabIndex property why was not work ? now , My TabIndex working properly. Additionally , I am add some control focus after postback was occurred. The following code was i am used after focusing.

if (IsPostBack)
      {
          Control ctrl = GetControlThatCausedPostBack(this.Page);

          if (ctrl != null)
              ctrl.Focus();
      }

/// <summary>
    /// Retrieves the control that caused the postback.
    /// </summary>
    /// <param name="page"></param>
    /// <returns></returns>
    private Control GetControlThatCausedPostBack(Page page)
    {
        //initialize a control and set it to null
        Control ctrl = null;

        //get the event target name and find the control
        string ctrlName = page.Request.Params.Get("__EVENTTARGET");
        if (!String.IsNullOrEmpty(ctrlName))
            ctrl = page.FindControl(ctrlName);

        //return the control to the calling method
        return ctrl;
    }

Thanks for all of your valuable comments..