[WordPress] Redirect WordPress Admin to a Custom Admin Page

00-redirect.php

<?php

/**
 * Redirect to the page from which we came (which should always be the
 * admin page. If the referred isn't set, then we redirect the user to
 * the login page).
 *
 * @access private
 * @param  bool $success Optional If success is false, then the information can't be saved.
 */
private function redirect( $success = true ) {

	// To make the Coding Standards happy, we have to initialize this.
	if ( ! isset( $_POST['_wp_http_referer'] ) ) { // Input var okay.
		$_POST['_wp_http_referer'] = wp_login_url();
	}

	// Sanitize the value of the $_POST collection for the Coding Standards.
	$url = sanitize_text_field(
		wp_unslash( $_POST['_wp_http_referer'] ) // Input var okay.
	);

	$url = ( ! $success ) ?
		esc_url( remove_query_arg( 'settings-saved', $url ) ) :
		add_query_arg( 'settings-saved', 'true', $url );

	wp_safe_redirect( urldecode( $url ) );
	exit;
}