WordPress create custom advanced dashboard widget

Add the following code to functions.php

//-------------dashboard widget advanced

add_action ( 'wp_dashboard_setup', 'my_note_dashboard_widget' );

function my_note_dashboard_widget() {
    wp_add_dashboard_widget ( 
            'my_note_dashboard_widget', 
            'My Note', 
            'display_my_note_dashboard_widget', 
            'update_my_note_dashboard_widget' 
    );
    
}

// display
function display_my_note_dashboard_widget() {
    // get saved data
    $widget_options = get_option ( 'my_note_dashboard_widget_options_note' );
    
    if ($widget_options) {
        echo   '<div class="my-css-class">'. $widget_options . "</div>";
    }
}

// edit
function update_my_note_dashboard_widget() {
    // get saved data
    $widget_options = get_option ( 'my_note_dashboard_widget_options_note' );
    
    // process update
    if (isset ( $_POST ) && isset ( $_POST['my_note_dashboard_widget_options_note'] )) {
        // save update
        update_option ( 'my_note_dashboard_widget_options_note', $_POST['my_note_dashboard_widget_options_note'] );
    }
    
    ?>
    Note <br> 
    <textarea 
    	name="my_note_dashboard_widget_options_note"
		style="width: 100%"><?php echo isset($widget_options) ? $widget_options : ''; ?></textarea>

	<?php
}

//-------------end dashboard widget advanced

Output

Related topics

• WordPress create custom dashboard widget – https://wiki.workassis.com/wordpress-create-custom-dashboard-widget/
• WordPress create custom dashboard widget using meta box – https://wiki.workassis.com/wordpress-create-custom-dashboard-widget-using-meta-box/

ref: https://codex.wordpress.org/Function_Reference/wp_add_dashboard_widget