Adding an Activity to a Chatter Feed Using a Trigger

I have had many requests for a trigger like this over time and Kevin Swiggum had a post back in 2010 with a simple to implement solution for this request, the link is below.

http://www.radialweb.com/2010/09/adding-activity-to-a-chatter-feed-using-triggers/


Below is a copy of the code Kevin posted:

trigger ChatterActivity on Task (after insert, after update) {

    List<FeedItem> feedItems = new List<FeedItem>();

    //We want to show the User name as assignedTo. The only way to get to that is by querying the user table.
    Set<ID> ownerIds = new Set<ID>();
    for (Task t : Trigger.new) {
        ownerIds.add(t.ownerId);
    }
    Map<ID,User> userMap = new Map<ID,User>([SELECT ID, Name FROM User WHERE ID IN :ownerIds]); //This is our user map

    //Now loop though the new/updated tasks and create the feed posts
    for (Task t : Trigger.new) {
        if (t.WhatId != null) {
            FeedItem fitem = new FeedItem();
            fitem.type = 'LinkPost';
            fitem.ParentId = t.WhatId;
            fitem.LinkUrl = '/' + t.id; //This is the url to take the user to the activity
            fitem.Title = 'View';  //This is the title that displays for the LinkUrl

            //Get the user by checking the userMap we created earlier
            User assignedTo = userMap.get(t.ownerId);

            fitem.Body = ((Trigger.isInsert) ? 'New' : 'Updated') + ' Activity ' + ((t.ActivityDate != null) ? t.ActivityDate.format() :'')
                        + '\nAssigned To: ' + ((assignedTo != null) ? assignedTo.name : 'Unknown')
                        + '\nSubject: ' + t.Subject
                        + '\nStatus: ' + t.Status;

            feedItems.add(fitem);
        }
    }

    //Save the FeedItems all at once.
    if (feedItems.size() > 0) {
        Database.insert(feedItems,false); //notice the false value. This will allow some to fail if Chatter isn't available on that object
    }
}

And here is the test class associated

public with sharing class ChatterUnitTests {

    /*
    *    Test the ChatterActivity trigger which inserts chatter feed posts whenever a task is inserted on the parent object
    */
    public static testMethod void testChatterActivity() {
        //create the test account
        Account a = new Account(name='Test Account');
        insert a;

        //create a task on that account
        Task t = new Task(whatId=a.id);
        t.Subject = 'This is a test activity for chatter';
        t.ActivityDate = System.today();
        t.Status = 'In Progress';
        t.Description = 'Hello, this will be chattered';

        insert t;

        //Make sure Account has the feed enabled. If it does, make sure the chatter feed post is there
        Schema.DescribeSObjectResult r = Account.SObjectType.getDescribe();
        if (r.isFeedEnabled()) {
            List<AccountFeed> posts = [SELECT Id, Type FROM AccountFeed WHERE ParentId = :a.id];
            System.assertEquals(1, posts.size());
        }
    }
}