public function updateCMSActions(FieldList $actions)
    {
        $checkInButton = new LiteralField('StartCheckIn',
            "<a class='action ss-ui-button ui-button ui-widget ui-state-default ui-corner-all ui-button-text-only'
                id='Edit_StartCheckIn'
                role='button'
                href='{$this->owner->Link('checkin')}'
                target='_blank'>
                Start check in
            </a>"
        );

        if ($this->owner->Attendees()->exists()) {
            $actions->push($checkInButton);
        }
    }
public function updateCMSActions(FieldList $actions)
    {
        $checkInButton = new LiteralField('StartCheckIn',
            "<a class='action ss-ui-button ui-button ui-widget ui-state-default ui-corner-all ui-button-text-only'
                id='Edit_StartCheckIn'
                role='button'
                href='{$this->owner->Link('checkin')}'
                target='_blank'>
                Start check in
            </a>"
        );

        if ($this->owner->Attendees()->exists()) {
            $actions->push($checkInButton);
        }
    }
public function updateCMSActions ( FieldList $ actions ) { $ checkInButton = new LiteralField ( 'StartCheckIn' , "<a class='action ss-ui-button ui-button ui-widget ui-state-default ui-corner-all ui-button-text-only'
                id='Edit_StartCheckIn'
                role='button'
                href='{$this->owner->Link('checkin')}'
                target='_blank'>
                Start check in
            </a>" ) ; if ( $ this -> owner -> Attendees ( ) -> exists ( ) ) { $ actions -> push ( $ checkInButton ) ; } }
Extend the page actions with an start check in action

@param FieldList $actions
Extend the page actions with an start check in action