Trigger to count the number of Contacts associated with an Account and display the Contacts count on the Account's custom field. trigger ContactTrigger on Contact (after insert, after update, after delete, after undelete) { if (Trigger.isAfter) { if (Trigger.isInsert || Trigger.isUndelete) { ContactTriggerHandler.countContacts(Trigger.new, null); } else if (Trigger.isUpdate) { ContactTriggerHandler.countContacts(Trigger.new, Trigger.oldMap); } else if (Trigger.isDelete) { ContactTriggerHandler.countContacts(null, Trigger.oldMap); } } } public class ContactTriggerHandler { public static void countContacts(List<Contact...