Featured Image in Header of Archive Pages in Twenty Eleven

To show the ‘featured image’ of the top post as header image in an archive page in the Twenty Eleven theme, edit header.php in the child theme;

change this section:

<?php
/*
* The header image.
* Check if this is a post or page, if it has a thumbnail, and if it's a big one
*/
if ( is_singular() && has_post_thumbnail( $post->ID ) &&
( /* $src, $width, $height */ $image = wp_get_attachment_image_src( get_post_thumbnail_id( $post->ID ), array( $header_image_width, $header_image_width ) ) ) &&
$image[1] >= $header_image_width ) :
// Houston, we have a new header image!
echo get_the_post_thumbnail( $post->ID, 'post-thumbnail' );
else :
// Compatibility with versions of WordPress prior to 3.4.
if ( function_exists( 'get_custom_header' ) ) {
$header_image_width  = get_custom_header()->width;
$header_image_height = get_custom_header()->height;
} else {
$header_image_width  = HEADER_IMAGE_WIDTH;
$header_image_height = HEADER_IMAGE_HEIGHT;
}
?>
<img src="<?php header_image(); ?>" width="<?php echo $header_image_width; ?>" height="<?php echo $header_image_height; ?>" alt="" />
<?php endif; // end check for featured image or standard header ?>

to:

<?php
/*
* The header image.
* Check if this is an archive and if the latest post has a thumbnail, and if it's a big one
* or Check if this is a post or page, if it has a thumbnail, and if it's a big one
*/
if ( is_archive() ) :
the_post();
$archive_thumb = '';
if( has_post_thumbnail( $post->ID ) &&
( /* $src, $width, $height */ $image = wp_get_attachment_image_src( get_post_thumbnail_id( $post->ID ), array( $header_image_width, $header_image_width ) ) ) &&
$image[1] >= $header_image_width ) :
$archive_thumb = get_the_post_thumbnail( $post->ID, 'post-thumbnail' );
endif;
rewind_posts();
endif;
if ( is_archive() && $archive_thumb ) :
echo $archive_thumb; //the featured image of the latest post in the archive
elseif ( is_singular() && has_post_thumbnail( $post->ID ) &&
( /* $src, $width, $height */ $image = wp_get_attachment_image_src( get_post_thumbnail_id( $post->ID ), array( $header_image_width, $header_image_width ) ) ) &&
$image[1] >= $header_image_width ) :
// Houston, we have a new header image!
echo get_the_post_thumbnail( $post->ID, 'post-thumbnail' );
else :
// Compatibility with versions of WordPress prior to 3.4.
if ( function_exists( 'get_custom_header' ) ) {
$header_image_width  = get_custom_header()->width;
$header_image_height = get_custom_header()->height;
} else {
$header_image_width  = HEADER_IMAGE_WIDTH;
$header_image_height = HEADER_IMAGE_HEIGHT;
}
?>
<img src="<?php header_image(); ?>" width="<?php echo $header_image_width; ?>" height="<?php echo $header_image_height; ?>" alt="" />
<?php endif; // end check for featured image or standard header ?>

Alphabetize Category Posts Using ‘pre_get_posts’ Action

Occasionally you want to have a different sort order in some of the category archives, for example, you want to output the posts of a specific category in alphabetical order.
Instead of having to create a category template for each of those categories and to add a custom query to change the query parameters, WordPress providdes the ‘pre_get_posts’ action where you can add a corresponding function:

function category_archive_sort_alphabetical( $query ) {
    if ( is_admin() || ! $query->is_main_query() )
        return;

    if ( is_category( array( 'Category One', 'category-two', 'Another Cat' ) ) ) {
		$query->set( 'orderby', 'title' );
		$query->set( 'order', 'ASC' );
        return;
    }
}
add_action( 'pre_get_posts', 'category_archive_sort_alphabetical', 1 );

resources:
http://codex.wordpress.org/Plugin_API/Action_Reference/pre_get_posts
http://codex.wordpress.org/Function_Reference/is_category

WordPress Changing Pluggable Functions Without Child Theme

A new concept (?) – to change a pluggable function of a WordPress theme without creating a child theme.

Example – to remove the  post tags output from the posts of Twenty Twelve.

Often, these things can be done by editing the styles of the theme, however in this case, CSS would not work as the tags don’t have their own CSS class.

Creating a child theme is usually recommended as the easiest option; but this might be over the top if the only changed paremeters are from some pluggable functions.

The alternative way would be to create a plugin to alter (in this example) the post-meta-data output, which is done through the function ‘twentytwelve_entry_meta()’.

How to:
use FTP to create a file, for example with the file name twentytwelve-entry-meta-modified.php, in the /wp-content/plugins/ folder; and add this example code (http://pastebin.com/7dMVvC9E)

<?php
/*
Plugin Name: Entry Meta Twenty Twelve Modified
Plugin URI: n/a
Description: personalization of the entry meta of Twenty Twelve without child theme; in this particular example the removal of the tags.
Version: 1.0
Author: alchymyth
Author URI: http://transformationpowertools.com
License: GPL2
*/

add_action( 'setup_theme', 'modify_pluggable_theme_functions' );

function modify_pluggable_theme_functions() {

if( wp_get_theme() == 'Twenty Twelve' && get_stylesheet_directory() == get_template_directory() ) :
//check for the right theme and that no child theme is used
function twentytwelve_entry_meta() {
// Translators: used between list items, there is a space after the comma.
$categories_list = get_the_category_list( __( ', ', 'twentytwelve' ) );

$date = sprintf( '<a href="%1$s" title="%2$s" rel="bookmark"><time datetime="%3$s">%4$s</time></a>',
esc_url( get_permalink() ),
esc_attr( get_the_time() ),
esc_attr( get_the_date( 'c' ) ),
esc_html( get_the_date() )
);

$author = sprintf( '<span><a href="%1$s" title="%2$s" rel="author">%3$s</a></span>',
esc_url( get_author_posts_url( get_the_author_meta( 'ID' ) ) ),
esc_attr( sprintf( __( 'View all posts by %s', 'twentytwelve' ), get_the_author() ) ),
get_the_author()
);

if ( $categories_list ) {
$utility_text = 'This entry was posted in %1$s on %2$s<span> by %3$s</span>.';
} else {
$utility_text = 'This entry was posted on %2$s<span> by %3$s</span>.';
}

printf(
$utility_text,
$categories_list,
$date,
$author
);
}
endif;
}
?>

The code checks that Twenty Twelve is the active theme, and that no child theme is activated.

Activate the plugin ‘Entry Meta Twenty Twelve Modified’ as usual from within dashboard – plugins.

http://codex.wordpress.org/Pluggable_Functions
http://codex.wordpress.org/FTP_Clients
http://codex.wordpress.org/Plugins
http://codex.wordpress.org/Writing_a_Plugin
http://codex.wordpress.org/Plugin_API/Action_Reference

Linking or Enqueuing Stylesheet in WordPress Themes

There are several ways of adding a stylesheet to a WordPress theme;
examples:

A: linking the stylesheet (in the head section of header.php)

– linking the main stylesheet style.css:

<link rel="stylesheet" type="text/css" media="all" href="<?php bloginfo( 'stylesheet_url' ); ?>" />

or

<link rel="stylesheet" type="text/css" media="all" href="<?php echo get_stylesheet_directory(); ?>" />

– linking another stylesheet custom.css:

<link rel="stylesheet" type="text/css" media="all" href="<?php echo get_stylesheet_directory_uri(); ?>/custom.css" />

B: enqueuing the stylesheet (in functions.php)

– enqueuing the main stylesheet style.css of a theme:

function theme_styles() {
	wp_enqueue_style( 'theme-style', get_stylesheet_uri() );
}
add_action( 'wp_enqueue_scripts', 'theme_styles' );

– enqueuing another stylesheet custom.css of a child theme:

function child_theme_styles() {
	wp_enqueue_style( 'custom-style', get_stylesheet_directory_uri() . '/custom.css' );
}
add_action( 'wp_enqueue_scripts', 'child_theme_styles', 20 );

C: using @import in an existing stylesheet

– example linking the parent theme’s style.css in a child theme’s style.css

@import url('../parentheme/style.css');

Resources:

WordPress Theme Development – style.css

link html
enqueue stylesheet
@import