It sounds like you have some of your Settings API calls wrong. Your dropdown input is created in the callback of your add_settings_field(). Each settings field needs to be told which settings section it is part of, and then your options page communicates which settings sections it needs to display through the do_settings() function.
Here's a short code example using a checkbox (omitting a few of the callback functions, but ALL of your callbacks need to be valid functions-- even if you make them empty functions):
function plugin_admin_init()
{
//Register your plugin's options with the Settings API, this will be important when you write your options page callback, sanitizing callback omitted
register_setting( 'plugin_options_group', 'plugin_options_name', 'sanitizing_callback' );
//Add a new settings section, section callback omitted
add_settings_section( 'section_id', 'Plugin Settings', 'section_callback', 'section_options_page_type' );
//Add a new settings field
add_settings_field( 'plugin_checkbox', 'Send automated emails?', 'field_callback', 'section_options_page_type', 'section_id' );
}
add_action('admin_init', 'plugin_admin_init');
function field_callback()
{
//The key thing that makes it a checkbox or textbox is the input type attribute. The thing that links it to my plugin option is the name I pass it.
echo "<input id='plugin_checkbox' name='plugin_options_name[plugin_checkbox]' type='checkbox' value='true' />"
}
function setup_menu()
{
add_menu_page('Page Name', 'Page Name', 'user_capability_level', 'page_slug', 'page_callback');
}
add_action('admin_menu', 'setup_menu');
function page_callback()
{
?>
<div class='wrap'>
<h2>Page Name</h2>
<form method='post' action='options.php'>
<?php
//Must be same name as the name you registered with register_setting()
settings_fields('plugin_options_group');
//Must match the type of the section you want to display
do_settings_section('section_options_page_type');
?>
<p class='submit'>
<input name='submit' type='submit' id='submit' class='button-primary' value='<?php _e("Save Changes") ?>' />
</p>
</form>
</div>
<?php
}
?>
