BuddyPress.org

Thanks @danbp, adding the scope and uncommenting those args worked! (Though leaving the item_id commented doesn’t appear to make a difference. I read on one of the codex pages for another function that item_id is optional?).

Is it normal for there to be no CSS associated with new tabs? It doesn’t seem to even show the default CSS for an activity page? If thats not normal does that mean the templates loaded are wrong or am i missing something else?

For anyone looking to do the same as me the working code is below:

//Function for new My Favourites tab
function bpmc_my_favourites_setup_nav() {
	global $bp;
	$parent_slug = 'my_favourites';
	$child_slug = 'favourites_sub';	
	
	//Add nav item
	bp_core_new_nav_item( array(
	'name' 					=> __( 'My Favourites' ),
	'slug' 					=> $parent_slug,
	'screen_function' 		=> 'bpmc_my_favourites_screen',
	'position' 				=> 100,
	'default_subnav_slug' 	=> $child_slug 
	) );
}

function bpmc_my_favourites_screen() {	
	add_action( 'bp_template_content', 'bpmc_my_favourites_screen_content' );
	bp_core_load_template( apply_filters( 'bp_core_template_plugin', 'members/single/plugins' ) );
}

function bpmc_my_favourites_screen_content() {
	do_action( 'my_favorites' );
}

add_action( 'bp_setup_nav', 'bpmc_my_favourites_setup_nav' );

function bpmc_get_favorites() {
	$activity_id = bp_activity_get_activity_id( array(
		'user_id' 				=> bp_loggedin_user_id(),
		'component'    			=> 'activity',
		'item_id' 		  		=> 0, //optional, zero is default value
	) );
	
	if ( ! $activity_id ) {
		return '';
	}

	//Activity loop
	if ( bp_has_activities( $activity_id . '&scope=favorites&max=10' )  ) :
		while ( bp_activities() ) : bp_the_activity();
			bp_get_template_part( 'activity/entry');
		endwhile;
	endif;
}

add_action ( 'my_favorites', 'bpmc_get_favorites' ); 

///////////////////////////////////////////////////////////////////////////////

//Function for new My Mentions nav tab
function bpmc_my_mentions_setup_nav() {
	global $bp;
	$parent_slug = 'my_mentions';
	$child_slug = 'mentions_sub';	
	
	//Add nav item
	bp_core_new_nav_item( array(
	'name' => __( 'My Mentions' ),
	'slug' => $parent_slug,
	'screen_function' => 'bpmc_my_mentions_screen',
	'position' => 110,
	'default_subnav_slug' => $child_slug 
	) );
}

function bpmc_my_mentions_screen() {	
	add_action( 'bp_template_content', 'bpmc_my_mentions_screen_content' );
	bp_core_load_template( apply_filters( 'bp_core_template_plugin', 'members/single/plugins' ) );
}

function bpmc_my_mentions_screen_content() {
	do_action( 'my_mentions' );
}

add_action( 'bp_setup_nav', 'bpmc_my_mentions_setup_nav' );

function bpmc_get_mentions() {
	$activity_id = bp_activity_get_activity_id( array(
		'user_id'				=> bp_loggedin_user_id(),
		'component'    			=> 'activity',
		'item_id'				=> 0, //optional, zero is default value
	) );
	
	if ( ! $activity_id ) {
		return '';
	}

	//Activity loop
	if ( bp_has_activities( $activity_id . '&scope=mentions&max=10' )  ) :
		while ( bp_activities() ) : bp_the_activity();
			bp_get_template_part( 'activity/entry');
		endwhile;
	endif;
}

add_action ( 'my_mentions', 'bpmc_get_mentions' );