hit the serverside event from javascript

JS:-
__doPostBack('ctl00$SiteContentPlaceHolder$searchTextBox','SearchTextBoxKeyPress');

C#:-
inside pageload

if (this.IsPostBack)
{
string eventArgument = (this.Request["__EVENTARGUMENT"] == null) ? string.Empty : this.Request["__EVENTARGUMENT"];
if (eventArgument.Trim() == "SearchTextBoxKeyPress")
{
_setFocus = true;
SearchTextBoxKeyPress(selectTabHiddenField.Value);
}
else
{
_setFocus = false;
}
}