But you can solve the problem with a Hook in the registry of your Framework/Basic-Theme.

//Code of the Framework to register 2 Sidebars
function xtreme_register_dynamic_sidebars() {
  register_sidebar( array(
    'name' => 'Sidebar One',
    'id' => 'sidebar-one',
    'description' => 'Sidebar One',
    'before_widget' => '<li id="%1$s" class="widget %2$s">',
    'after_widget' => '</li>',
    'before_title' => '<h5 class="widget-title">',
    'after_title' => '</h5>'
    ));
  register_sidebar( array(
    'name' => 'Sidebar Two',
    'id' => 'sidebar-two',
    'description' => 'Sidebar Two',
    'before_widget' => '  <li id="%1$s" class="widget %2$s">',
    'after_widget' => '</li>',
    'before_title' => '<h5 class="widget-title">',
    'after_title' => '</h5>'
    ));
  do_action('childtheme_sidebars');
}
add_action( 'widgets_init', 'xtreme_register_dynamic_sidebars' );

You see the Hook do_action('childtheme_sidebars');
let's use this Hook:

//functions.php im Child-Theme
function xtreme_unregister_sidebar() {
    unregister_sidebar('sidebar-two');
}
add_action( 'childtheme_sidebars', 'xtreme_unregister_sidebar' );

And the Sidebar is removed. Easy huh?

Here a screenshot of all setting possibilities:

And this is how it would look like on your blog:

Even though, this idea seemed to be easy to realize. It was a piece of work. I don't want you to be bored, so I'm not explaining the whole code, but I just want go in detail on some details, what I had to consider to make this Widget workable.

I check the date if it's valid ( 2009/02/30 doesn't exist). Then I had to avoid division by zero, if the Widget is active but doesn't include any values yet. For the correct formatting of the saved money depending on the language I used the WordPress function number_format_i18n:

$saved = number_format_i18n($packs * $price, 2);

Unfortunately, there is no feature in WordPress, which displays the currencies correctly (but I guess, this is probably not necessary). Therefore, I added a field "Currency position" with the values "before" and "after", so that the currency will be displayed properly, depending on the country. The year field automatically displays the current year minus 5 years, so that the widget is also current in 100 years.
The rest are fields for entering the text output before and after values.

Installation

Unzip file wpe_quit_smoking_widget.zip and copy it to wp-content/plugins/ , then activate it in your backend. After that the Widget will be available in your Widgets area.

Please Note: The Widget needs WordPress Version 2.8 or higher, otherwise it won't be displayed.

Download

Download WPEngineer Quit Smoking Widget

Have fun with the Widget and good luck with your goal to stop smoking! The team of WP Engineer wish you all Happy Holidays!

If you use widgets in your theme and this also accommodates a variety of hierarchies, you will quickly realize that it really only makes sense to output HTML for the widgets when the widget area is also used by the user.

Ian Stewart, the developer of the Theme-Framework Thematic found an elegant solution, but you can use it even without the framework.
You just need one function, which is similar to the Conditional Tags of WordPress. Put this function in your functions.php of your theme.

function is_sidebar_active($index) {
	global $wp_registered_sidebars;

	$widgetcolums = wp_get_sidebars_widgets();

	if ($widgetcolums[$index])
		return true;

	return false;
}

It uses the output of your widget area, if there is content.

A query could look like this in your template:

<?php if ( function_exists('is_sidebar_active') && is_sidebar_active('sidebar') ) { ?>
	<div id="sidebar">
		<ul>
			<?php dynamic_sidebar('sidebar'); ?>
		</ul>
	</div>
<?php } ?>

The above example loads the content only, if the widget area with the ID sidebar has content, that means if widgets are used in this area.

Especially in Germany we have the tradition of an Advent Calendar. An Advent calendar is a special calendar which is used to count down the days from December the 1st to Christmas Eve December 24th.

An Advent Calendar has 24 doors, one of which is opened every day during Advent. Each door opens to reveal an image, a poem, or part of a story such as the Nativity story itself. More elaborate Advent calendars have a small gift concealed in each door, such as a toy or a chocolate item.

At WP Engineer, we thought we should do the same and open a door every day, which contains a little gift for our readers, by providing them a WordPress tip or trick each day. So we hope you will be exciting to see what tip, hack or news will be behind the door the next morning. Enjoy a new little WordPress gift every day until December 24th.

Our first little gift is a code snippet to implement the commentform as a widget in your sidebar. This Widget only works with WordPress 2.8 and higher since it's using the new Widget API. Just paste the code in the functions.php of your theme and drag the Widget on your sidebar.

<?php
class wpe_comment_widget extends WP_Widget {

    function wpe_comment_widget() {
        $widget_ops = array('classname' => 'wpe_widget_comments', 'description' => __( 'Your comments and commentform', 'your_textdomain') );
        $this->WP_Widget('wpe-comment-widget', __('WPE Comments', 'your_textdomain'), $widget_ops);
    }

    function widget($args, $instance) {
        if(is_single()) {
            extract($args);
            global $post;
            echo $before_widget;
            comments_template();
            echo $after_widget;
        }
    }

    function update($new_instance, $old_instance) {
        $instance = $old_instance;
        return $instance;
    }

    function form($instance) {
        ?>
        <p><?php _e('This widget will only be displayed in single view.', 'your_textdomain'); ?></p>
       <?php
    }
}

register_widget('wpe_comment_widget');
?>

You can disable the unneccessary Widgets in your functions.php of your theme with a small function. The following syntax will switch off all the standard widgets. It should therefore be adjusted depending on your requirements:

// unregister all default WP Widgets
function unregister_default_wp_widgets() {

	unregister_widget('WP_Widget_Pages');

	unregister_widget('WP_Widget_Calendar');

	unregister_widget('WP_Widget_Archives');

	unregister_widget('WP_Widget_Links');

	unregister_widget('WP_Widget_Meta');

	unregister_widget('WP_Widget_Search');

	unregister_widget('WP_Widget_Text');

	unregister_widget('WP_Widget_Categories');

	unregister_widget('WP_Widget_Recent_Posts');

	unregister_widget('WP_Widget_Recent_Comments');

	unregister_widget('WP_Widget_RSS');

	unregister_widget('WP_Widget_Tag_Cloud');
}

add_action('widgets_init', 'unregister_default_wp_widgets', 1);

The function unregister_widget() needs as parameters the class, therefore the code is working since version 2.8 only. In prior versions, Widgets were supported differently.

How to create your own Widgets since WordPress Version 2.8 is explained in Build A WordPress 2.8 Widget With The New Widget API.

It is a Post Navigation Widget, which lists in the single post view (single.php) a specific number of posts which were published before this post and a certain number of posts which were published after this post. I think this is a nice way to show older posts in the sidebar. Here's a screenshot, left of the backend, right of the sidebar:

I created a query to check if the class WP_Widget even exists, so the user won't get any error messages in WordPress versions prior to 2.8.

<?php
if (class_exists('WP_Widget')) {
    class WPE_Widget_Post_Navigation extends WP_Widget {

        function WPE_Widget_Post_Navigation() {
            $widget_ops = array('classname' => 'wpe_widget_post_navi', 'description' => __( "Some posts before and after the current post") );
            $this->WP_Widget('wpe-post-navi', __('WPE Single Post Navigation'), $widget_ops);
        }

        function widget($args, $instance) {
            if(is_single()) {
                global $post, $wpdb;
                extract($args);

                if ( !$number = (int) $instance['number'] )
                    $number = 5;
                elseif( $number < 1 )
                    $number = 1;
                elseif( $number > 10 )
                    $number = 10;

                $title_before 		= apply_filters('widget_title', empty($instance['title_before']) ? 'Posts before' : $instance['title_before']);
                $title_after	 	= apply_filters('widget_title', empty($instance['title_after']) ? 'Posts after' : $instance['title_after']);
                $before_widget_2	= preg_replace("/(wpe\-post\-navi-\d+)/", "$1-1", $before_widget);

                $querystr = "
                    SELECT *
                    FROM $wpdb->posts wposts
                    WHERE wposts.ID != $post->ID
                    AND wposts.post_type = 'post'
                    AND wposts.post_status = 'publish'
                    AND wposts.post_date %s '$post->post_date'
                    ORDER BY wposts.post_date %s
                    LIMIT $number
                 ";

                $leading_posts = $wpdb->get_results(sprintf($querystr, '<', 'DESC'), OBJECT);
                $trailing_posts = $wpdb->get_results(sprintf($querystr, '>', 'ASC'), OBJECT);

                if ($trailing_posts && count($trailing_posts)) {
                    echo $before_widget_2 . $before_title . $title_before . $after_title . "<ul>";
                    $trailing_posts = array_reverse($trailing_posts);
                    foreach ($trailing_posts as $post) {
                        setup_postdata($post);
                        ?> <li><a href="<?php the_permalink() ?>" title="<?php echo esc_attr(get_the_title() ? get_the_title() : get_the_ID()); ?>"><?php if ( get_the_title() ) the_title(); else the_ID(); ?> </a></li><?php
                    }
                    echo "</ul>" . $after_widget;
                }

                if ($leading_posts && count($leading_posts)) {
                    echo $before_widget . $before_title . $title_after . $after_title . "<ul>";
                    foreach ($leading_posts as $post) {
                        setup_postdata($post);
                        ?> <li><a href="<?php the_permalink() ?>" title="<?php echo esc_attr(get_the_title() ? get_the_title() : get_the_ID()); ?>"><?php if ( get_the_title() ) the_title(); else the_ID(); ?> </a></li><?php
                    }
                    echo "</ul>" . $after_widget;
                }
                wp_reset_query();
            }
        }

        function update( $new_instance, $old_instance ) {
            $instance = $old_instance;
            $instance['title_before'] = strip_tags($new_instance['title_before']);
            $instance['number'] = (int) $new_instance['number'];
            $instance['title_after'] = strip_tags($new_instance['title_after']);

            return $instance;
        }
        function form( $instance ) {
            $title_before = ($instance['title_before'] == '') ? 'Posts before' : esc_attr($instance['title_before']);
            $title_after = ($instance['title_after'] == '') ? 'Posts after' : esc_attr($instance['title_after']);
            if ( !$number = (int) $instance['number'] )
                $number = 5;
            elseif ( $number < 1 )
                $number = 1;
            elseif ( $number > 10 )
                $number = 10;
    ?>
            <p><label for="<?php echo $this->get_field_id('title_before'); ?>">Title before:</label>
            <input class="widefat" id="<?php echo $this->get_field_id('title_before'); ?>" name="<?php echo $this->get_field_name('title_before'); ?>" type="text" value="<?php echo $title_before; ?>" /></p>
            <p><label for="<?php echo $this->get_field_id('title_after'); ?>">Title after:</label>
            <input class="widefat" id="<?php echo $this->get_field_id('title_after'); ?>" name="<?php echo $this->get_field_name('title_after'); ?>" type="text" value="<?php echo $title_after; ?>" /></p>
            <p><label for="<?php echo $this->get_field_id('number'); ?>">Number of posts to show before and after current post:</label>
            <input id="<?php echo $this->get_field_id('number'); ?>" name="<?php echo $this->get_field_name('number'); ?>" type="text" value="<?php echo $number; ?>" size="3" /><br />
            <small>(at most 10)</small></p>
    <?php
        }
    }
    register_widget('WPE_Widget_Post_Navigation');
}
?>

Most of this should be self-explanatory. Now to the function widget () , which does the actual work. Here we had to do a little trick, because the widget actually creates 2 widgets, and they would get the same ID. That wouldn't be valid, so the code adds a -1 to one of the widget elements:

$before_widget_2 = preg_replace("/(wpe\-post\-navi-\d+)/", "$1-1", $before_widget);

2 queries are getting executed. One for the posts before this post and one for the posts after this post. if posts are available they will show up on the sidebar.

Download Widget.
Then unpack and copy the code into functions.php. Please note, the widget is for WordPress 2.8.

The work of every author is different and the dashboard is the center of information. Therefore we have decided to supplement a widget in the Dashboard, which shows the last five drafts of all authors. I enhanced the existing Plugin Draft Feed.

• It provides a feed of all drafts
• And the last 5 drafts of all authors in the Dashboard.

Everybody who needs something like this, can download this Plugin from my German Blog. It doesn't have any options and doesn't exist in SVN of WordPress - if you want you can use and expand it or leave a comment if you have a question. Enjoy!

Also new is that the sidebar now saves or updates via AJAX. Here is a Screenshot from the current development version:

You can find the widget API in wp-includes/widget.php and the widgets itself in wp-includes/default-widgets.php. The class WP_Widget provides the functionality of the widgets, and each widget must be inherited. The class WP_Widget_Factory is for registration and instantiation of widgets responsible.

How to create a widget in WordPress 2.8?

It will be a simple example and will output the links for the RSS Feed of the articles and comments. In functions.php we first create the skeleton of our widgets:

class My_RSS_Widget extends WP_Widget {
	function My_RSS_Widget() {
		//Constructor
	}

	function widget($args, $instance) {
		// prints the widget
	}

	function update($new_instance, $old_instance) {
		//save the widget
	}

	function form($instance) {
		//widgetform in backend
	}
}
register_widget('My_RSS_Widget');

We have a class My_RSS_Widget created, which inherits the properties and methods of the WP_Widget class (extends). In a new widget, the methods widget and update always have to be created, form is optional. With register_widget ( 'My_RSS_Widget') will be the widget registered. Let's fill up our widget.

class My_RSS_Widget extends WP_Widget {
	function My_RSS_Widget() {
		$widget_ops = array('classname' => 'widget_rss_links', 'description' => 'A list with your feeds links' );
		$this->WP_Widget('rss_links', 'Feed links', $widget_ops);
	}

	function widget($args, $instance) {
		extract($args, EXTR_SKIP);

		echo $before_widget;
		$title = empty($instance['title']) ? ' ' : apply_filters('widget_title', $instance['title']);
		$entry_title = empty($instance['entry_title']) ? ' ' : apply_filters('widget_entry_title', $instance['entry_title']);
		$comments_title = empty($instance['comments_title']) ? ' ' : apply_filters('widget_comments_title', $instance['comments_title']);

		if ( !empty( $title ) ) { echo $before_title . $title . $after_title; };
		echo '<ul id="rss">';
		echo '  <li><a href=" ' . get_bloginfo('rss2_url') . '" rel="nofollow" title=" ' . $entry_title . ' ">' . $entry_title . '</a></li>';
		echo '  <li><a href=" ' . get_bloginfo('comments_rss2_url') . '" rel="nofollow" title="  '. $comments_title . ' ">' . $comments_title . '</a></li>';
		echo '</ul>';
		echo $after_widget;
	}

	function update($new_instance, $old_instance) {
		$instance = $old_instance;
		$instance['title'] = strip_tags($new_instance['title']);
		$instance['entry_title'] = strip_tags($new_instance['entry_title']);
		$instance['comments_title'] = strip_tags($new_instance['comments_title']);

		return $instance;
	}

	function form($instance) {
		$instance = wp_parse_args( (array) $instance, array( 'title' => '', 'entry_title' => '', 'comments_title' => '' ) );
		$title = strip_tags($instance['title']);
		$entry_title = strip_tags($instance['entry_title']);
		$comments_title = strip_tags($instance['comments_title']);
?>
			<p><label for="<?php echo $this->get_field_id('title'); ?>">Title: <input class="widefat" id="<?php echo $this->get_field_id('title'); ?>" name="<?php echo $this->get_field_name('title'); ?>" type="text" value="<?php echo attribute_escape($title); ?>" /></label></p>
			<p><label for="<?php echo $this->get_field_id('entry_title'); ?>">Title for entry feed: <input class="widefat" id="<?php echo $this->get_field_id('entry_title'); ?>" name="<?php echo $this->get_field_name('entry_title'); ?>" type="text" value="<?php echo attribute_escape($entry_title); ?>" /></label></p>
			<p><label for="<?php echo $this->get_field_id('comments_title'); ?>">Title for comments feed: <input class="widefat" id="<?php echo $this->get_field_id('comments_title'); ?>" name="<?php echo $this->get_field_name('comments_title'); ?>" type="text" value="<?php echo attribute_escape($comments_title); ?>" /></label></p>
<?php
	}
}
register_widget('My_RSS_Widget');

The widget feature is for the output in the frontend to examine the update data and stores an instance of the widget and form creates in the backend the input mask, which in our case for the title of the widget and the displayed link text.

The code is self-explanatory. The function widget is for the output in the frontend responsible, update examine the data and stores an instance of the widget and form creates in the backend the input mask, which in our case for the title of the widget and the displayed link text.

So now implement your own ideas!

Please check out the post WordPress 2.8 Single Post Navigation Widget for a more advanced example.

if ( function_exists('register_sidebar') )
    register_sidebar(array(
        'before_widget' => '<li id="%1$s" class="widget %2$s">',
        'after_widget' => '</li>',
        'before_title' => '<h2 class="widgettitle">',
        'after_title' => '</h2>',
    ));

As we all know, there is the function register_sidebar since version 2.2. My question is: How long do you want to ask if this function exists? The default theme of WordPress 2.7 doesn't ask, if have_comments (a new template tag of version 2.7) exists, but it asks if register_sidebar exists. I just suppose the developers just forgot it and everybody in the world thinks, that it has to be like that.

Please don't misunderstand, the query isn't wrong, but in my opinion just useless in the default theme of version 2.7

Since we are already talking about the register_sidebar and it's use, the code of a premium theme uses this query even 3 times:

<?php
if ( function_exists('register_sidebar') )
register_sidebar(array('name'=>'Home Sidebar',
'before_widget' => '<div class="block">',
'after_widget' => '</div><div class="blockfooter"></div>',
'before_title' => '<h3>',
'after_title' => '</h3>',
));
?>
<?php
if ( function_exists('register_sidebar') )
register_sidebar(array('name'=>'Post Sidebar',
'before_widget' => '<div class="block">',
'after_widget' => '</div><div class="blockfooter"></div>',
'before_title' => '<h3>',
'after_title' => '</h3>',
));
?>
<?php
if ( function_exists('register_sidebar') )
register_sidebar(array('name'=>'Page Sidebar',
'before_widget' => '<div class="block">',
'after_widget' => '</div><div class="blockfooter"></div>',
'before_title' => '<h3>',
'after_title' => '</h3>',
));
?>

This is not really a good example for a premium theme. First, why closing the PHP tag after every function and open it before every function again?
Second, if the function register_sidebar exist in first place, it will also exist the 2nd time
and third, the code is almost identical except the name of the sidebar. That could be done much easier:

<?php
$sidebars = array('Home Sidebar', 'Post Sidebar', 'Page Sidebar');
foreach($sidebars as $sb) {
	register_sidebar(array('name'=> $sb,
		'before_widget' => '<div class="block">',
		'after_widget' => '</div><div class="blockfooter"></div>',
		'before_title' => '<h3>',
		'after_title' => '</h3>',
	));
}
?>

As I said, it's not wrong and I didn't mean it as it is a bad way to code, but sometimes you can do it much easier