如何通过用户ID检查WordPress是否在线？

Question

I want to show an online status on my website if an other user is online. So for example if user A wants to know if user B is available, I want to show an online sign.

I know that there is a function in WordPress called is_user_logged_in() but this function works only for the current user. https://developer.wordpress.org/reference/functions/is_user_logged_in/ So is there anyone who has an idea how I can get this done?

This is the logic:

if ( user_online( $user_id ) ) {
    return 'Online';
} else {
    return 'Absent';
}

Answer 1

You might use Transients API to get users's status. Create a user-online-update function that you hook on init . For example:

// get logged-in users
$logged_in_users = get_transient('online_status');

// get current user ID
$user = wp_get_current_user();

// check if the current user needs to update his online status;
// status no need to update if user exist in the list
// and if his "last activity" was less than let's say ...15 minutes ago  
$no_need_to_update = isset($logged_in_users[$user->ID]) 
    && $logged_in_users[$user->ID] >  (time() - (15 * 60));

// update the list if needed
if (!$no_need_to_update) {
  $logged_in_users[$user->ID] = time();
  set_transient('online_status', $logged_in_users, $expire_in = (30*60)); // 30 mins 
}

This should run on each page load, but the transient will be updated only if required. If you have a large number of users online you might want to increase the "last activity" time frame to reduce db writes, but 15 minutes is more than enough for most sites.

Now to check if the user is online, simply look inside that transient to see if a certain user is online, just like you did above:

// get logged in users
$logged_in_users = get_transient('online_status');

// for eg. on author page
$user_to_check = get_query_var('author'); 

$online = isset($logged_in_users[$user_to_check])
   && ($logged_in_users[$user_to_check] >  (time() - (15 * 60)));

The transient expires in 30 minutes if there's no activity at all. But in case you have users online all the time it won't expire, so you might want to clean-up that transient periodically by hooking another function on a twice-daily event or something like that. This function would remove old $logged_in_users entries...

Source: https://wordpress.stackexchange.com/a/34434

Answer 2

    First get the user id of the user B by 

    $user_id_B = get_current_user_id();

    Now here give the condition for the particular user B to check whether he is online or not

if(is_user_logged_in()){
    if( $user_id_B == 'user id of B')
    {
        return 'Online'; (or echo 'online';)
    }
}
By this you will get the presence of user B.