Full example
A quick (mu-)plugin as example:
<?php
/** Plugin Name: Add Admin Bar Icon */
add_action( 'admin_bar_menu', function( \WP_Admin_Bar $bar )
{
$bar->add_menu( array(
'id' => 'wpse',
'parent' => null,
'group' => null,
'title' => __( 'Example', 'some-textdomain' ),
'href' => get_edit_profile_url( get_current_user_id() ),
'meta' => array(
'target' => '_self',
'title' => __( 'Hello', 'some-textdomain' ),
'html' => '<p>Hello</p>',
'class' => 'wpse--item',
'rel' => 'friend',
'onclick' => "alert('Hello');",
'tabindex' => PHP_INT_MAX,
),
) );
} );
Which renders the following HTML as first element (and therefore also renders our admin bar useless, but that's not the point of this example):
<li id="wp-admin-bar-wpse" class="wpse--item">
<a class="ab-item" tabindex="9223372036854775807" href="http://astro.dev/wp-admin/profile.php" onclick="alert(\'Hello\');" target="_self" title="Hello" rel="friend">Example</a>
<p>Hello</p>
</li>
Now that we got a base, we can care about...
Adding Icons
The sad news: There is no easy way to do it. At least not without adding your own stylesheet. As you can read (in the code), there are some things happening: I prepended the HTML needed to wrap a Dashicon before the actual item. Then I added a very high integer as last number to the action - that's what decides the position of the item in the admin bar.
<?php
/** Plugin Name: Add Admin Bar Icon */
add_action( 'admin_bar_menu', function( \WP_Admin_Bar $bar )
{
$bar->add_menu( array(
'id' => 'wpse',
'title' => '<span class="ab-icon"></span>'.__( 'Example', 'some-textdomain' ),
'href' => get_edit_profile_url( get_current_user_id() ),
'meta' => array(
'target' => '_self',
'title' => __( 'Ahoi!', 'some-textdomain' ),
'html' => '<!-- Custom HTML that goes below the item -->',
),
) );
}, 210 ); // <-- THIS INTEGER DECIDES WHERE THE ITEM GETS ADDED (Low = left, High = right)
add_action( 'wp_enqueue_scripts', function()
{
wp_enqueue_style( /* register your stylesheet */ );
}
Finally you will need to add some CSS rules in your own stylesheet. The only moving part is the wpse in the #/id. The rest is constant and equal for all admin bar items/nodes. You might also need to adjust the top position to fit the Dashicon. Just choose a Dashicon from their site and add the fXXX code in the CSS below.
#wpadminbar #wp-admin-bar-wpse .ab-icon:before {
font: normal 20px/1 dashicons;
content: '\f306';
position: relative;
float: left;
speak: never;
padding: 4px 0;
-webkit-font-smoothing: antialiased;
-moz-osx-font-smoothing: grayscale;
background-image: none !important;
margin-right: 6px;
}