Make Widget appear on Dashboard

Question

I recently created a widget in my functions.php with following code :

register_sidebar(
    array(
        'name'          => __( 'Informations importantes', 'twentynineteen' ),
        'id'            => 'informations-widget',
        'description'   => __( 'Ajouter ici le slider vous permettant de mettre en avant des informations complémentaires.', 'twentynineteen' ),
        'before_widget' => '<section id="%1$s" class="widget %2$s">',
        'after_widget'  => '</section>',
        'before_title'  => '<h2 class="widget-title">',
        'after_title'   => '</h2>',
    )
);

No problem at this point, it appears normally on the Appearance -> Widgets section

Well now, i have an issue when i try to make it appear on my dashboard i can add a custom widget without any problem, but make an existing appear on dashboard it is a little more difficult. I tried with this code ( with 'informations widget' as the idea of the original widget :

add_action('wp_dashboard_setup', 'my_custom_dashboard_widgets');
function my_custom_dashboard_widgets() {

add_meta_box('informations-widget', 'Dashboard Widget Title', 

'custom_dashboard_infos', 'dashboard', 'side', 'high');
    }

function custom_dashboard_infos() {
echo '<p>Une infos importantes';
}

Thanks in advance for the help !

Answer 1

Widgets aren't metaboxes, they can't be added to the dashboard directly.

wp_add_dashboard_widget expects a callable function, not a sidebar ID. You can't plug a widget or a widget area/sidebar into a function like that.

Instead, you would need to add a metabox, then, in its callback display what you wanted to display, e.g.

add_action('wp_dashboard_setup', 'custom_dashboard_widgets'); 
function custom_dashboard_widgets() {
    global $wp_meta_boxes;
    wp_add_dashboard_widget('custom_dashboard_box', 'Example', 'custom_dashboard_box');
}
function custom_dashboard_box() {
    // Widget Content Here
    echo '<p>Hello World</p>';
}

You could then call the_widget inside the callback to display an individual widget with predefined parameters.

Additionally, your questions code registers a sidebar, not a widget. If it's the displaying of a widget area in the dashboard that you want, that is not what you asked. Please update your question accordingly.