I need to add the DropDownField to the searchform which shows only the pages from the top level. Even I want to restrict the pages from the toplevel to list only specific pages.
How to do that? I did not get useful links or document .Please help
function SearchForm() {
$searchText = isset($_REQUEST['Search']) ? $_REQUEST['Search'] : 'Search';
$fields = new FieldSet(
new TextField("Search", "", $searchText)
new DropdownField("PageID", "", Dataobject::get("ContentPage")->map("ID", "Title", "Please Select"))
);
$actions = new FieldSet(
new FormAction('results', 'Search')
);

return new SearchForm($this->owner, "SearchForm", $fields, $actions);
}

I listed the top level pages new DropdownField("PageID", "", DataObject::get("SiteTree", "\"ShowInMenus\" = 1 AND \"ParentID\" = 0")->map("ID", "Title", "Please Select"))

<option value="2">Company</option>
<option value="3">Film</option>
<option value="7169">Advertising</option>
<option value="17880">Forum</option>
<option value="15">Technical Support</option>
<option value="17885">Wiki</option>
<option value="5299">Training</option>
<option value="17882">Forum</option>
<option value="4281">Security</option>

How could I filter to show only pages Company,Film and Advertising?

Could you not just add a boolean field ShowInSearchDropdown to the Page class settings? That way you can add whatever page you want...

Thank you giving a thought of adding a ShowInSearchDropdown column to the table. I would try that later currently I am modifying the code to

DropdownField("PageID", "", DataObject::get("SiteTree", "\"ShowInMenus\" = 1 AND \"ParentID\" = 0 AND Title NOT IN ('Technical Support','Forum','Wiki')")->map("ID", "Title", "Please Select"))

This still works to me.