Merged PR 55056: Initialise active tab on submit

## What's being changed

We have moved the initialization of the page tabs to the render function and added a new options register hook.

## Why it's being changed

The page initialize was being called on every page load, even if it was not part of the DD plugin.

## How to review / test this change

1. Ensure the plugin is not registering a page tab on every load, only the page intended.
2. Ensure the page save function works as expected.

Related work items: #258420

admin/class-dotdigital-wordpress-admin.php

@@ -121,15 +121,9 @@ public function render_tab_links() {
 	 * @return void
 	 */
 	public function add_plugin_page_tabs() {
-		if ( ! $this->is_dd_wp_settings_page() ) {
-			return;
-		}
 		foreach ( $this->available_page_tabs as $page_tab ) {
 			try {
 				$tab = new $page_tab();
-				if ( $this->is_current_tab( $tab ) ) {
-					$tab->initialise();
-				}
 				$this->page_tabs[ $tab->get_slug() ] = $tab;
 			} catch ( \Exception $e ) {
 				error_log( $e );
@@ -139,13 +133,30 @@ public function add_plugin_page_tabs() {
 	}
 
 	/**
-	 * Render the active tab for the settings page.
+	 * Ensure the form has been properly registered on submission.
+	 *
+	 * @return void
+	 */
+	public function add_plugin_page_submission_initialisation() {
+		global $pagenow;
+
+		if ( 'options.php' === $pagenow && isset( $_POST['option_page'] ) ) { // phpcs:ignore WordPress.Security.NonceVerification.Missing
+			$option_page = sanitize_text_field( wp_unslash( $_POST['option_page'] ) ); // phpcs:ignore WordPress.Security.NonceVerification.Missing
+			if ( isset( $this->page_tabs[ $option_page ] ) ) {
+				$this->page_tabs[ $option_page ]->initialise();
+			}
+		}
+	}
+
+	/**
+	 * Render and initialise the active tab for the settings page.
 	 *
 	 * @return void
 	 */
 	public function render_active_tab() {
 		foreach ( $this->page_tabs as $page_tab ) {
 			if ( $this->is_current_tab( $page_tab ) ) {
+				$page_tab->initialise();
 				$page_tab->render();
 			}
 		}
@@ -246,16 +257,6 @@ private static function dotdigital_item_sort_desc( object $a, object $b ) {
 		return $a_name > $b_name ? -1 : 1;
 	}
 
-	/**
-	 * Check if current page is ?page=dotdigital-for-wordpress-settings
-	 *
-	 * @return bool
-	 */
-	private function is_dd_wp_settings_page() {
-		return isset( $_GET['page'] ) &&
-			   strpos( sanitize_text_field( wp_unslash( $_GET['page'] ) ), Dotdigital_WordPress_Settings_Admin::URL_SLUG ) !== false;
-	}
-
 	/**
 	 * Check if current tab is in query string
 	 *

includes/class-dotdigital-wordpress.php

@@ -174,9 +174,10 @@ private function define_admin_hooks() {
 		$plugin_admin = new Dotdigital_WordPress_Admin( $this->get_plugin_name(), $this->get_version() );
 		$this->loader->add_action( 'admin_enqueue_scripts', $plugin_admin, 'enqueue_styles' );
 		$this->loader->add_action( 'admin_enqueue_scripts', $plugin_admin, 'enqueue_scripts' );
+		$this->loader->add_action( 'admin_init', $plugin_admin, 'add_plugin_page_submission_initialisation', 1 );
+		$this->loader->add_action( 'admin_init', $plugin_admin, 'add_plugin_admin_page_actions' );
+		$this->loader->add_action( 'admin_menu', $plugin_admin, 'add_plugin_page_tabs' );
 		$this->loader->add_action( 'admin_menu', $plugin_admin, 'add_plugin_admin_menus' );
-		$this->loader->add_action( 'admin_menu', $plugin_admin, 'add_plugin_admin_page_actions', 5 );
-		$this->loader->add_action( 'admin_menu', $plugin_admin, 'add_plugin_page_tabs', 5 );
 	}
 
 	/**