Create Chatter Post and @mention User in Trigger

Question

I have a trigger that creates a chatter post after insert or after update for Tasks. However, I also want to @mention the created by user for the task. How Can I add this? Thanks

trigger ActivityHistoryToChatter on Task (after insert, after update) {
for(Task t : trigger.new)
{
    //if it's now a completed task, and wasn't  before
    //create the new chatter post.
    string what = t.whatID;

    if(what.substring(0,3) == 'a19') 
    /*
        The above line lets you control exactly which objects you want to toss this on. Adjust the If statement to the 
        3 digit object code for various elements.

        Ex:

        Cases - 500
        Accounts - 001
        Opportunities - 006

        I STRONGLY suggest you use this if you're going to do a larger, longer demo, as you'll need to chatter enable any 
        object you play with the task history on or this will crash. If you're not playing with Activity History/Tasks anywhere
        else, won't be a big deal.
    */

    //{
        if(!t.alreadyPosted__c && t.status == 'Completed')//hasn't been posted, completed
        {
            Task daTask = [select id, description, whoid, activityDate, ownerid, subject from Task where id = :t.id];
            string whoelement = daTask.whoId;
            if (whoelement != NULL)
            {
            if(whoElement.substring(0,3) == '003')//contact
                {Contact who = [select name from Contact where id = :whoelement];
                whoElement = who.name;}
            else
                {Lead who2 = [select name from Lead where id = :whoelement];
                whoElement= who2.name;}
            }                   
        User owner = [select name from User where id = :daTask.OwnerId];

        daTask.alreadyPosted__c = true; 

        FeedPost OppFeed = new FeedPost();
        string body = t.Subject + ' was completed by ' + owner.name + ' on ';
        body += t.activityDate.Month() + '/' + t.activityDate.Day() + '/' + t.ActivityDate.Year() + '\n';
        if(t.description != null)
            body += 'Comments: ' + t.description;
        OppFeed.body = body;
        oppFeed.parentID = t.whatID;
        oppFeed.linkURL = '/' + t.id;
        oppFeed.title = t.subject;
        insert oppFeed;
        }
    //}
}

Answer 1

The only way to @mention someone in apex is using the ConnectApi (AKA Chatter in apex) and not by just creating a FeedItem in apex. You'll need to refactor most everything in your code around the posting to Chatter. Here is a code sample of a text post with a mention borrowed from an example that Jeff Douglas has on his blog:

// makes a simple chatter text post to the specified user from the running user 
public static void mentionTextPost(Id userId, Id userToMentionId, String postText) { 

   ConnectApi.MessageBodyInput messageInput = new ConnectApi.MessageBodyInput();
   messageInput.messageSegments = new List();

   // add some text before the mention
   ConnectApi.TextSegmentInput textSegment = new ConnectApi.TextSegmentInput();
   textSegment.text = 'Hey ';
   messageInput.messageSegments.add(textSegment);

   // add the mention
   ConnectApi.MentionSegmentInput mentionSegment = new ConnectApi.MentionSegmentInput();
   mentionSegment.id = userToMentionId;
   messageInput.messageSegments.add(mentionSegment);

   // add the text that was passed
   textSegment = new ConnectApi.TextSegmentInput();
   textSegment.text = postText;
   messageInput.messageSegments.add(textSegment);

   ConnectApi.FeedItemInput input = new ConnectApi.FeedItemInput();
   input.body = messageInput;

   // post it
   ConnectApi.ChatterFeeds.postFeedItem(null, ConnectApi.FeedType.UserProfile, userId, input, null);

}  

Lastly, it's worth noting that you can only post as the running user. It's not possible to post on anyone else's behalf.

• With credit to Jeff, posted on his blog here, Chatter for Apex Code Examples