wordpress add custom admin page with data submit and receive.

add_custom_admin_page.php

/*
	add custom admin page;
	http://codex.wordpress.org/Function_Reference/add_menu_page
*/
add_action( 'admin_menu', 'register_my_custom_menu_page' );

function register_my_custom_menu_page(){
	/*
		args: 
			$page_title, 
			$menu_title, 
			$capability, 
			$menu_slug, 
			$function, 
			$icon_url, 
			$position
	*/
    add_menu_page( 'custom menu title', 'custom menu', 'manage_options', 'custompage', 'my_custom_menu_page', plugins_url( 'myplugin/images/icon.png' ), 6 ); 
}

function my_custom_menu_page(){
	
// 	$content = '[gallery ids="5"]';
	$content = get_page( 2 );

	
	/*
		add POST Request respon.
		http://wordpress.stackexchange.com/questions/10500/how-do-i-best-handle-custom-plugin-page-actions
	*/

	if ( $_SERVER["REQUEST_METHOD"] == "POST" && isset($_POST['submit'])) {
		echo "posted <br>";
		$content = $_POST['erik_editor'];
	}
    echo "Admin Page Test";	
    echo '<form id="contactForm" method="post">';
    
    $args = array(
    	'quicktags' => false,
    	'dfw' => true, 'tabfocus_elements' => 'sample-permalink,post-preview', 'editor_height' => 360
	);
 
	wp_editor( $content->post_content, 'erik_editor', $args );
	submit_button( 'Save content' );
	 echo '</form>';
}