public class MyTextBox : TextBox,IPostBackEventHandler
{

public event EventHandler KeyDown;
protected void OnKeyDown(EventArgs e)
{
if (KeyDown != null)
{
KeyDown(this, e);
}
}

public event EventHandler Blur;
protected void OnBlur(EventArgs e)
{
if (Blur != null)
{
Blur(this, e);
}
}

void IPostBackEventHandler.RaisePostBackEvent(string eventArgument)
{
postBackEvent(eventArgument);
}

private void postBackEvent(string argument)
{
switch (argument)
{
case "onkeydown":
OnKeyDown(new EventArgs());
break;
case "onblur":
OnBlur(new EventArgs());
break;
}
}

protected override void AddAttributesToRender(System.Web.UI.HtmlTextWriter writer)
{
base.AddAttributesToRender(writer);
writer.AddAttribute("onblur", Page.ClientScript.GetPostBackEventReference(this, "onblur"));
writer.AddAttribute("onkeydown", Page.ClientScript.GetPostBackEventReference(this, "onkeydown"));
}

}