Implement CMB2_Ajax as a singleton.

CMB2_Ajax is already being used as a singleton, but doesn't enforce it which leads to the static `hooks()` function, so let's enforce it and be done with it.

includes/CMB2_Ajax.php

@@ -21,28 +21,34 @@ class CMB2_Ajax {
 	protected $ajax_update = false;
 
 	/**
-	 * Constructor
-	 * @since 2.2.0
+	 * Instance of this class
+	 * @since 2.2.2
+	 * @var object
 	 */
-	public function __construct() {
-		self::hooks( $this );
-	}
+	protected static $instance;
 
 	/**
-	 * Hook in the oembed ajax handlers
-	 * @since  2.2.0
-	 * @param  CMB2_Ajax  $self This object (for hooking)
+	 * Get the singleton instance of this class
+	 * @since 2.2.2
+	 * @return object
 	 */
-	public static function hooks( $self ) {
-		static $hooked = false;
-
-		if ( ! $hooked ) {
-			add_action( 'wp_ajax_cmb2_oembed_handler', array( $self, 'oembed_handler' ) );
-			add_action( 'wp_ajax_nopriv_cmb2_oembed_handler', array( $self, 'oembed_handler' ) );
-			// Need to occasionally clean stale oembed cache data from the option value.
-			add_action( 'cmb2_save_options-page_fields', array( __CLASS__, 'clean_stale_options_page_oembeds' ) );
-			$hooked = true;
+	public static function get_instance() {
+		if ( ! ( self::$instance instanceof self ) ) {
+			self::$instance = new self();
 		}
+
+		return self::$instance;
+	}
+
+	/**
+	 * Constructor
+	 * @since 2.2.0
+	 */
+	protected function __construct() {
+		add_action( 'wp_ajax_cmb2_oembed_handler', array( $this, 'oembed_handler' ) );
+		add_action( 'wp_ajax_nopriv_cmb2_oembed_handler', array( $this, 'oembed_handler' ) );
+		// Need to occasionally clean stale oembed cache data from the option value.
+		add_action( 'cmb2_save_options-page_fields', array( __CLASS__, 'clean_stale_options_page_oembeds' ) );
 	}
 
 	/**

includes/helper-functions.php

@@ -50,7 +50,7 @@ function cmb2_utils() {
  */
 function cmb2_ajax() {
 	static $cmb2_ajax;
-	$cmb2_ajax = $cmb2_ajax ? $cmb2_ajax : new CMB2_Ajax();
+	$cmb2_ajax = $cmb2_ajax ? $cmb2_ajax : CMB2_Ajax::get_instance();
 	return $cmb2_ajax;
 }