How To Create Related Post WordPress Plugin

Some weeks ago i need to create releated post for single.php . After some tries and looking idea in the internet . Here is the plugin idea : find related post based on categories where related post based on post date before the post single which become the center

To do that we need function : is_single , wp_get_post_categories , get_posts , and add_filter for the_content to put related post under content.

Some Notes : to get post ID on single just use global $post , get_posts is used get post based on criterias, wp_get_post_categories to get categories of existing post

Because we need to convert post date we need function strtotime and date in Y-m-d format . Ok here is the full code :

<?php
/*
Plugin Name: ZZ Related Post
Plugin URI: http://www.wpamanuke.com
Description: Sample Related Post based on category
Version: 1.0.1po
Author: WPAmaNuke
Author URI: https://wpamanuke.com
*/

// ADD BOTTOM RELATED ARTICLE ON THE POST SINGLE
function zz_related_post() {
   // check if single
   if (is_single()) {
		global $post;
		
		$post_ids = [];
		$prev_post = get_previous_post();
		$next_post = get_next_post();
		$i = 0;
		$post_ids[$i] = $post->ID;
		$i++;
		if ($prev_post) {
			$post_ids[$i] = $prev_post->ID;
			$i++;
		}
		/*
		if ($next_post) {
			$post_ids[$i] = $next_post->ID;
		}
		*/
		
		$a = strtotime($post->post_date . " 0 month");
		$time = date("Y-m-d",$a);
		$cat = wp_get_post_categories($post->ID);
		
		
		$related = get_posts( 
			array( 
				'category__in' => $cat, 
				'numberposts' => 3, 
				'post__not_in' => $post_ids,
				//'meta_key'=>'_thumbnail_id',
				'orderby' => 'DATE',
				'order' => 'DESC',
				'date_query' => array(
					'before' => $time 
				)
			) 
		);
		
		
		if ($related) {
			echo '<div class="zz-related-post">';
			echo '<h3>Related Post</h3>';
			
			foreach( $related as $post ) {
				setup_postdata($post);
				?>
				<div class="zz-related-post_block">
				<article>
					<?php if ( has_post_thumbnail() ) { ?>
						<figure class="zz-related-post_image"> 
							<a class="zz-image-link" href="<?php the_permalink(); ?>" title="">
								<?php the_post_thumbnail( 'medium' ); ?>
							</a>
						</figure>
					<?php } ?>
					<div class="zz-related-post_title">
						<h4 class="zz-meta-title"><a href="<?php the_permalink(); ?>" title=""><?php the_title(); ?></a></h4>
					</div>
				</article>    
				</div>
				<?php
			}
			echo '</div>';
			
		}
		wp_reset_postdata();
   }
}
// End Function Related POST

function zz_after_content($content) {
	ob_start();
	zz_related_post();
	$after_content = ob_get_clean();
	$custom_content = $content . $after_content;
	return $custom_content;
}
add_filter( 'the_content', 'zz_after_content');


?>

Just see your single post . And Related post will be on the bottom after content.

How To Include Javascript and CSS on Shortcode WordPress Plugin

Some weeks ago i try to find to include javascript and css on a shortcode only when the file is needed. After some search on the internet here is which i think the most efficient way.

First we must register file resource which we need, so we can call in the shortcode using wp_register_script and wp_register_style

// First register resources with init 
function zz_shortcode_resource() {
	wp_register_script("zz-shortcode-jscss-script", plugins_url("script.js", __FILE__), array('jquery'), "1.0", false);
	wp_register_style("zz-shortcode-jscss-style", plugins_url("style.css", __FILE__), array(), "1.0", "all");
}
add_action( 'init', 'zz_shortcode_resource' );

After that we call our shortcode function with wp_enqueue_script and wp_enqueue_style

add_shortcode( 'zz_shortcode_jscss', 'zz_shortcode_jscss' );
function zz_shortcode_jscss( $attr , $content) {
	$a = shortcode_atts( array(
	  'text' => ''
	), $attr );
	wp_enqueue_script( 'jquery' );
	wp_enqueue_script("zz-shortcode-jscss-script",array('jquery') , '1.0', true);
	wp_enqueue_style("zz-shortcode-jscss-style");
	return '<div class="zz-sc-jscss">' . $a['text'] .'</div>';
}

Here is the complete source code in plugin so you can use it :

<?php
/*
Plugin Name: ZZ Shortcode With JS and CSS
Plugin URI: http://www.wpamanuke.com
Description: Include Javascript File and CSS Files on the Shortcode . Example [zz_shortcode_jscss text="HELLO CODE"][/zz_shortcode_jscss]
Version: 1.0.1
Author: WPAmaNuke
Author URI: https://wpamanuke.com
*/

// First register resources with init 
function zz_shortcode_resource() {
	wp_register_script("zz-shortcode-jscss-script", plugins_url("script.js", __FILE__), array('jquery'), "1.0", false);
	wp_register_style("zz-shortcode-jscss-style", plugins_url("style.css", __FILE__), array(), "1.0", "all");
}
add_action( 'init', 'zz_shortcode_resource' );

add_shortcode( 'zz_shortcode_jscss', 'zz_shortcode_jscss' );
function zz_shortcode_jscss( $attr , $content) {
	$a = shortcode_atts( array(
	  'text' => ''
	), $attr );
	wp_enqueue_script( 'jquery' );
	wp_enqueue_script("zz-shortcode-jscss-script",array('jquery') , '1.0', true);
	wp_enqueue_style("zz-shortcode-jscss-style");
	return '<div class="zz-sc-jscss">' . $a['text'] .'</div>';
}

Here is the style.css . Because it’s only sample , so we need only little css to show that it is working

.zz-sc-jscss {
	padding:30px;
	background-color:#ff0000;
	color:#ffffff;
}

For javascript script.js . Just showing alert for simple showing the code working

jQuery( document ).ready(function($) {
	alert('This is from shortcode with js and css');
});

Ok. That’s how to include javascript and css on shortcode. I just record it , so if sometime i will need it , i just see this blog records

How To Create Dashboard Widget WordPress Plugin

Dashboard widget is widget which is shown in the administration dashboard.

Code which ussualy used :

  • wp_add_dashboard_widget
  • add_action , wp_dashboard_setup

The minimalist code which can be used :

/**
 * Add a widget to the dashboard.
 *
 * This function is hooked into the 'wp_dashboard_setup' action below.
 */
function zz_add_dashboard_widgets() {

	wp_add_dashboard_widget(
                 'zz_dashboard_widget',         // Widget slug.
                 'ZZ Dashboard Widget',         // Title.
                 'zz_dashboard_widget_function' // Display function.
        );	
}
add_action( 'wp_dashboard_setup', 'zz_add_dashboard_widgets' );

/**
 * Create the function to output the contents of our Dashboard Widget.
 */
function zz_dashboard_widget_function() {

	// Display whatever it is you want to show.
	echo "<h2>RSS Feed</h2>";
	output_rss_feed('http://wpamanuke.com/?feed=rss', 5, true, true, 200);
}

Complete Code

<?php
/*
Plugin Name: ZZ Dashboard Widgets
Plugin URI: http://www.wpamanuke.com
Description: Sample Dashboard Widgets Code
Version: 1.0.1
Author: WPAmaNuke
Author URI: https://wpamanuke.com
*/

/**
 * Add a widget to the dashboard.
 *
 * This function is hooked into the 'wp_dashboard_setup' action below.
 */
function zz_add_dashboard_widgets() {

	wp_add_dashboard_widget(
                 'zz_dashboard_widget',         // Widget slug.
                 'ZZ Dashboard Widget',         // Title.
                 'zz_dashboard_widget_function' // Display function.
        );	
}
add_action( 'wp_dashboard_setup', 'zz_add_dashboard_widgets' );

/**
 * Create the function to output the contents of our Dashboard Widget.
 */
function zz_dashboard_widget_function() {

	// Display whatever it is you want to show.
	echo "<h2>RSS Feed</h2>";
	output_rss_feed('http://wpamanuke.com/?feed=rss', 5, true, true, 200);
}

function get_rss_feed_as_html($feed_url, $max_item_cnt = 10, $show_date = true, $show_description = true, $max_words = 0)
{
    $result = "";
    // get feeds and parse items
    $rss = new DOMDocument();
	$rss->load($feed_url);

    $feed = array();
    foreach ($rss->getElementsByTagName('item') as $node) {
        $item = array (
            'title' => $node->getElementsByTagName('title')->item(0)->nodeValue,
            'desc' => $node->getElementsByTagName('description')->item(0)->nodeValue,
            'content' => $node->getElementsByTagName('description')->item(0)->nodeValue,
            'link' => $node->getElementsByTagName('link')->item(0)->nodeValue,
            'date' => $node->getElementsByTagName('pubDate')->item(0)->nodeValue,
        );
        $content = $node->getElementsByTagName('encoded'); // <content:encoded>
        if ($content->length > 0) {
            $item['content'] = $content->item(0)->nodeValue;
        }
        array_push($feed, $item);
    }
    // real good count
    if ($max_item_cnt > count($feed)) {
        $max_item_cnt = count($feed);
    }
    $result .= '<ul class="feed-lists">';
    for ($x=0;$x<$max_item_cnt;$x++) {
        $title = str_replace(' & ', ' & ', $feed[$x]['title']);
        $link = $feed[$x]['link'];
        $result .= '<li class="feed-item">';
        $result .= '<div class="feed-title"><strong><a href="'.$link.'" title="'.$title.'">'.$title.'</a></strong></div>';
        if ($show_date) {
            $date = date('l F d, Y', strtotime($feed[$x]['date']));
            $result .= '<small class="feed-date"><em>Posted on '.$date.'</em></small>';
        }
        if ($show_description) {
            $description = $feed[$x]['desc'];
            $content = $feed[$x]['content'];
            // find the img
            $has_image = preg_match('/<img.+src=[\'"](?P<src>.+?)[\'"].*>/i', $content, $image);
            // no html tags
            $description = strip_tags(preg_replace('/(<(script|style)\b[^>]*>).*?(<\/\2>)/s', "$1$3", $description), '');
            // whether cut by number of words
            if ($max_words > 0) {
                $arr = explode(' ', $description);
                if ($max_words < count($arr)) {
                    $description = '';
                    $w_cnt = 0;
                    foreach($arr as $w) {
                        $description .= $w . ' ';
                        $w_cnt = $w_cnt + 1;
                        if ($w_cnt == $max_words) {
                            break;
                        }
                    }
                    $description .= " ...";
                }
            }
            // add img if it exists
            if ($has_image == 1) {
                $description = '<img class="feed-item-image" src="' . $image['src'] . '" />' . $description;
            }
            $result .= '<div class="feed-description">' . $description;
            $result .= ' <a href="'.$link.'" title="'.$title.'">Continue Reading »</a>'.'</div>';
        }
        $result .= '</li>';
    }
    $result .= '</ul>';
    return $result;
}
function output_rss_feed($feed_url, $max_item_cnt = 10, $show_date = true, $show_description = true, $max_words = 0)
{
    echo get_rss_feed_as_html($feed_url, $max_item_cnt, $show_date, $show_description, $max_words);
}

How To Create Custom Post Type WordPress Plugin

In WordPress, post and page represent contents for website. Taxonomy are categories for posts. You can create your won custom post type with plugin.

Some codes which we will use :

  • register_post_type
  • register_taxonomy
  • add_filter, single_template, taxonomy_template

Code to create custom post type

function wporg_custom_post_type()
{
    register_post_type('wporg_product',
                       array(
                           'labels'      => array(
                               'name'          => __('Products'),
                               'singular_name' => __('Product'),
                           ),
                           'public'      => true,
                           'has_archive' => true,
                           'rewrite'     => array( 'slug' => 'products' ), // my custom slug
                       )
    );
}
add_action('init', 'wporg_custom_post_type');

Code to create taxonomy

function wporg_register_taxonomy_course()
{
    $labels = [
        'name'              => _x('Courses', 'taxonomy general name'),
		'singular_name'     => _x('Course', 'taxonomy singular name'),
		'search_items'      => __('Search Courses'),
		'all_items'         => __('All Courses'),
		'parent_item'       => __('Parent Course'),
		'parent_item_colon' => __('Parent Course:'),
		'edit_item'         => __('Edit Course'),
		'update_item'       => __('Update Course'),
		'add_new_item'      => __('Add New Course'),
		'new_item_name'     => __('New Course Name'),
		'menu_name'         => __('Course'),
		];
	$args = [
		'hierarchical'      => true, // make it hierarchical (like categories)
		'labels'            => $labels,
		'show_ui'           => true,
		'show_admin_column' => true,
		'query_var'         => true,
		'rewrite'           => ['slug' => 'course'],
	];
	register_taxonomy('course', ['wporg_product'], $args);
}
add_action('init', 'wporg_register_taxonomy_course');

if you want to use template in plugin folder :

add_filter('single_template','your_single_template_function');
add_filter( 'taxonomy_template','your_taxonomy_template_function');

Here is the full code and don’t forget to change permalink after you activate the plugin, otherwise it will show 404 page :

<?php
/*
Plugin Name: ZZ Custom Post
Plugin URI: http://www.wpamanuke.com
Description: Sample Custom Post
Version: 1.0.1
Author: WPAmaNuke
Author URI: https://wpamanuke.com
*/

define( 'ZZ_PRODUCT_DIR' , plugin_dir_path( __FILE__ ) );
function wporg_custom_post_type()
{
    register_post_type('wporg_product',
                       array(
                           'labels'      => array(
                               'name'          => __('Products'),
                               'singular_name' => __('Product'),
                           ),
                           'public'      => true,
                           'has_archive' => true,
                           'rewrite'     => array( 'slug' => 'products' ), // my custom slug
                       )
    );
}
add_action('init', 'wporg_custom_post_type');


/* Filter the single_template with our custom function*/
add_filter('single_template', 'my_custom_template');


function my_custom_template($single) {

    global $post;

    /* Checks for single template by post type */
    if ( $post->post_type == 'wporg_product' ) {
        if ( file_exists( ZZ_PRODUCT_DIR . '/single.php' ) ) {
            return ZZ_PRODUCT_DIR . '/single.php';
        }
    }

    return $single;

}


function wporg_register_taxonomy_course()
{
    $labels = [
        'name'              => _x('Courses', 'taxonomy general name'),
		'singular_name'     => _x('Course', 'taxonomy singular name'),
		'search_items'      => __('Search Courses'),
		'all_items'         => __('All Courses'),
		'parent_item'       => __('Parent Course'),
		'parent_item_colon' => __('Parent Course:'),
		'edit_item'         => __('Edit Course'),
		'update_item'       => __('Update Course'),
		'add_new_item'      => __('Add New Course'),
		'new_item_name'     => __('New Course Name'),
		'menu_name'         => __('Course'),
		];
	$args = [
		'hierarchical'      => true, // make it hierarchical (like categories)
		'labels'            => $labels,
		'show_ui'           => true,
		'show_admin_column' => true,
		'query_var'         => true,
		'rewrite'           => ['slug' => 'course'],
	];
	register_taxonomy('course', ['wporg_product'], $args);
}
add_action('init', 'wporg_register_taxonomy_course');

function my_custom_archive( $template ) {
	 $mytemplate = ZZ_PRODUCT_DIR . '/archive.php';

    if( is_tax( 'course') && is_readable( $mytemplate ) )
        $template =  $mytemplate;

    return $template;
}
add_filter( 'taxonomy_template', 'my_custom_archive');

single.php

<?php
$args = [
    'post_type'      => 'wporg_product',
    'posts_per_page' => 10,
];
$loop = new WP_Query($args);
while ($loop->have_posts()) {
    $loop->the_post();
    ?>
    <div class="entry-content">
        <?php the_title(); ?>
        <?php the_content(); ?>
    </div>
    <?php
}

archive.php

<?php
$args = [
    'post_type'      => 'wporg_product',
    'posts_per_page' => 10,
];
$loop = new WP_Query($args);
while ($loop->have_posts()) {
    $loop->the_post();
    ?>
    <div class="entry-content">
        <a href="<?php the_permalink(); ?>" title=""><?php the_title(); ?></a>
        <?php the_content(); ?>
    </div>
    <?php
}

How To Create WordPress Plugin With Ajax

Ajax is the acronym for Asynchronous JavaScript And XML. It’s very usefull if you want to reload specify information from web server. It purpose to reload part of data on the web , so we don’t need to reload all website

To use ajax in WordPress , you need to know PHP and jQuery. Here is some wordpress api which you need to know to use ajax in wordpress :

  • add_action with wp_enqueue_scripts , wp_ajax_your_variable, wp_ajax_nopriv_your_variable
  • wp_create_nonce
  • wp_localize_script : to create variable which needed in javascript
  • check_ajax_referrer : check if referrer from same server
  • wp_die

Here is zz-ajax.php code :

<?php
/*
Plugin Name: ZZ Ajax
Plugin URI: http://www.wpamanuke.com
Description: Sample Ajax
Version: 1.0.1
Author: WPAmaNuke
Author URI: https://wpamanuke.com
*/

add_action( 'wp_enqueue_scripts', 'zz_ajax_enqueue_scripts' );
function zz_ajax_enqueue_scripts() {
	wp_enqueue_script( 'jquery' );
	wp_enqueue_script( 'zz-ajax-script', plugins_url( '/test-ajax.js', __FILE__ ), array('jquery') , '1.0', true);
		
	$nonce = wp_create_nonce( 'zz_ajax_nonce' );
	wp_localize_script( 'zz-ajax-script', 'zz_ajax_var', array( 'ajax_url' => admin_url( 'admin-ajax.php' ) , 'nonce' => $nonce ) );
	
}

add_action( 'wp_ajax_zz_ajax_action', 'zz_ajax_action' );
add_action( 'wp_ajax_nopriv_zz_ajax_action', 'zz_ajax_action' );
function zz_ajax_action() {
	check_ajax_referer( 'zz_ajax_nonce' , '_ajax_nonce' );
	echo "This is ajax message 1234";
	wp_die(); // this is required to terminate immediately and return a proper response
}

test-ajax.js code

jQuery(document).ready(function($) {
	
	var data = {
		'_ajax_nonce': zz_ajax_var.nonce,
		'action': 'zz_ajax_action'
	};
	
	jQuery.post(zz_ajax_var.ajax_url, data, function(response) {
		alert('Got this from the server: ' + response);
	});
	
});

How To Create ShortCode WordPress Plugin

Shortcode are special code in wordpress to show specific function with easy efforts. Shortcode is begin with [ and end with ]. For example function which we will display amazon product with shortcode [azproduct]. With shortcode you can use function coloring easily, or if you need only specific parameter change, shortcode is perfect for your needs.

To enable shortcode you must register it with function :

add_shortcode( 'your_shortcode_name', 'your_shortcode_function' );
function your_shortcode_function($attr,$content) {
}

Here is sample amazon link shortcode code :

<?php
/*
Plugin Name: ZZ Amazon Product ShortCode
Plugin URI: http://www.wpamanuke.com
Description: Sample ShortCode Code
Version: 1.0.1
Author: WPAmaNuke
Author URI: https://wpamanuke.com
*/

add_shortcode( 'azproduct', 'azproduct_link' );

// The callback function that will replace [azproduct]
function azproduct_link( $attr ) {
	
	$asin = '0385495323';
	if ( isset( $attr['asin'] ) ) {
		$asin = $attr['asin'];
	}
	
	$title= 'Buy Now';
	if ( isset( $attr['title'] ) ) {
		$title = $attr['title'];
	}
	
	return '<a href="http://www.amazon.com/dp/'. $asin .'" > '. $title .' </a > ';
}

add_shortcode( 'azproduct_content', 'azproduct_content' );
function azproduct_content( $attr , $content) {
	$a = shortcode_atts( array(
	  'color' => '',
	  'bgcolor' => ''
	), $attr );
	
	return '<div style="color:'. $a['color'] .';background-color:' . $a['bgcolor'] .';">'. $content . '</div>';
}
You can use shortcode in your editor with code like this : 
[azproduct asin="1476755744" title="Red Notice"]
[azproduct_content color="#ff0000" bgcolor="#cc0cc0"]This is contents[/azproduct_content]

How To Create WordPress Widget Plugin

Widget is small block which perform specific function. Widget ussualy put in the sidebar or footer. You can list widgets which are ready in your wordpress from admin area Appearance ยป Widgets section in your WordPress dashboard.

To program widget here is some codes skeletons which you need to know

function your_register_widgets() {
	register_widget('your_widget_class');
}
add_action('widgets_init', 'your_register_widgets');

class your_widget_class extends WP_Widget {
	function __construct() {
	}
	function widget($args, $instance) {
	}
	function update($new_instance, $old_instance) {
	}
	function form($instance) {
	}
}
<?php
/*
Plugin Name: ZZ Widgets
Plugin URI: http://www.wpamanuke.com
Description: Sample Widgets Code
Version: 1.0.1
Author: WPAmaNuke
Author URI: https://wpamanuke.com
*/

function zz_register_widgets() {
	register_widget('zz_widget');
}
add_action('widgets_init', 'zz_register_widgets');

class zz_widget extends WP_Widget { 
	function __construct() {
		parent::__construct(
			'zz_widget', esc_html_x( 'ZZ Widget' , 'widget name', 'zz-widget' ),
			array(
				'classname' => 'zz-widget',
				'description' => esc_html__( 'ZZ Widget Post ' , 'zz-widget' ),
				'customize_selective_refresh' => true
			)
		);
	}
	function widget($args, $instance) {
		$defaults = array('title' => '', 'category' => 0, 'tags' => '', 'postcount' => 5, 'offset' => 0, 'sticky' => 1);
        $instance = wp_parse_args($instance, $defaults);
		$query_args = array();
		$query_args['ignore_sticky_posts'] = $instance['sticky'];
		if (0 !== $instance['category']) {
			$query_args['cat'] = $instance['category'];
		}
		if (!empty($instance['tags'])) {
			$tag_slugs = explode(',', $instance['tags']);
			$tag_slugs = array_map('trim', $tag_slugs);
			$query_args['tag_slug__in'] = $tag_slugs;
		}
		if (!empty($instance['postcount'])) {
			$query_args['posts_per_page'] = $instance['postcount'];
		}
		if (0 !== $instance['offset']) {
			$query_args['offset'] = $instance['offset'];
		}
	    
		$widget_posts = new WP_Query($query_args);
		echo wp_kses_post( $args['before_widget'] );
			if ($widget_posts->have_posts()) :
				$last = $widget_posts->post_count;
				$i = 0;
				if (!empty($instance['title'])) {
					$title = ! empty( $instance['title'] ) ? $instance['title'] : '';
					$title = apply_filters( 'widget_title', $title, $instance, $this->id_base );
					echo wp_kses_post( $args['before_title'] ) . esc_html( $title ) . wp_kses_post( $args['after_title'] );
				}
				echo '<ul class="zz-widget-block">' . "\n";
					while ($widget_posts->have_posts()) : $widget_posts->the_post();
						 echo "<li>
						<a href='";
						the_permalink();
						echo "'>";
						the_title();  
						echo "</a>
						</li>";
					endwhile;
				echo '</ul>' . "\n";
			endif;
			wp_reset_postdata();
			
		echo wp_kses_post( $args['after_widget'] );
		
    }
	function update($new_instance, $old_instance) {
        $instance = array();
        if (!empty($new_instance['title'])) {
			$instance['title'] = sanitize_text_field($new_instance['title']);
		}
        if (0 !== absint($new_instance['category'])) {
			$instance['category'] = absint($new_instance['category']);
		}
		if (!empty($new_instance['tags'])) {
			$tag_slugs = explode(',', $new_instance['tags']);
			$tag_slugs = array_map('sanitize_title', $tag_slugs);
			$instance['tags'] = implode(', ', $tag_slugs);
		}
		if (0 !== absint($new_instance['postcount'])) {
			if (absint($new_instance['postcount']) > 50) {
				$instance['postcount'] = 50;
			} else {
				$instance['postcount'] = absint($new_instance['postcount']);
			}
		}
		if (0 !== absint($new_instance['offset'])) {
			if (absint($new_instance['offset']) > 50) {
				$instance['offset'] = 50;
			} else {
				$instance['offset'] = absint($new_instance['offset']);
			}
		}
        return $instance;
    }
    function form($instance) {
        $defaults = array('title' => '', 'category' => 0, 'tags' => '', 'postcount' => 5, 'offset' => 0, 'sticky' => 1);
        $instance = wp_parse_args($instance, $defaults); ?>
        <p>
        	<label for="<?php echo esc_attr($this->get_field_id('title')); ?>"><?php esc_html_e('Title:', 'zz-widget'); ?></label>
			<input class="widefat" type="text" value="<?php echo esc_attr($instance['title']); ?>" name="<?php echo esc_attr($this->get_field_name('title')); ?>" id="<?php echo esc_attr($this->get_field_id('title')); ?>" />
        </p>
		<p>
            <label for="<?php echo esc_attr($this->get_field_id('category')); ?>"><?php esc_html_e('Select a Category:', 'zz-widget'); ?></label>
            <select id="<?php echo esc_attr($this->get_field_id('category')); ?>" class="widefat" name="<?php echo esc_attr($this->get_field_name('category')); ?>">
            	<option value="0" <?php selected(0, $instance['category']); ?>><?php esc_html_e('All', 'zz-widget'); ?></option><?php
            		$categories = get_categories();
            		foreach ($categories as $cat) { ?>
            			<option value="<?php echo absint($cat->cat_ID); ?>" <?php selected($cat->cat_ID, $instance['category']); ?>><?php echo esc_html($cat->cat_name) . ' (' . absint($cat->category_count) . ')'; ?></option><?php
            		} ?>
            </select>
            <small><?php esc_html_e('Select a category to display posts from.', 'zz-widget'); ?></small>
		</p>
		<p>
        	<label for="<?php echo esc_attr($this->get_field_id('tags')); ?>"><?php esc_html_e('Filter Posts by Tags (e.g. lifestyle):', 'zz-widget'); ?></label>
			<input class="widefat" type="text" value="<?php echo esc_attr($instance['tags']); ?>" name="<?php echo esc_attr($this->get_field_name('tags')); ?>" id="<?php echo esc_attr($this->get_field_id('tags')); ?>" />
	    </p>
        <p>
        	<label for="<?php echo esc_attr($this->get_field_id('postcount')); ?>"><?php esc_html_e('Post Count (max. 50):', 'zz-widget'); ?></label>
			<input class="widefat" type="text" value="<?php echo absint($instance['postcount']); ?>" name="<?php echo esc_attr($this->get_field_name('postcount')); ?>" id="<?php echo esc_attr($this->get_field_id('postcount')); ?>" />
	    </p>
	    <p>
        	<label for="<?php echo esc_attr($this->get_field_id('offset')); ?>"><?php esc_html_e('Skip Posts (max. 50):', 'zz-widget'); ?></label>
			<input class="widefat" type="text" value="<?php echo absint($instance['offset']); ?>" name="<?php echo esc_attr($this->get_field_name('offset')); ?>" id="<?php echo esc_attr($this->get_field_id('offset')); ?>" />
	    </p><?php
    }
}

Creating Meta Box In Post / Page

WordPress has metabox in post / page. Meta boxes is used to adding information in your post / page. To create meta box you need to know function add_meta_box, add_meta_boxes , wp_nonce_field, get_post_meta and save_post

<?php
/*
Plugin Name: ZZ Metabox
Plugin URI: http://www.wpamanuke.com
Description: Sample Metabox
Version: 1.0.1
Author: WPAmaNuke
Author URI: https://wpamanuke.com
*/

/**
 * Register meta box(es).
 */
function zz_register_meta_boxes() {
    add_meta_box( 'zz-meta-box-id', __( 'ZZ Meta Box', 'zz-metabox' ), 'zz_metaboxes_display_callback', 'post' );
}
add_action( 'add_meta_boxes', 'zz_register_meta_boxes' );
 
/**
 * Meta box display callback.
 *
 * @param WP_Post $post Current post object.
 */
function zz_metaboxes_display_callback( $post ) {
    // Display code/markup goes here. Don't forget to include nonces!
	
	// retrieve the custom meta box values
	$zz_price = get_post_meta( $post->ID, '_zz_price', true );
	$zz_plan = get_post_meta( $post->ID, '_zz_plan', true );
	//nonce for security
	wp_nonce_field( plugin_basename( __FILE__ ), 'zz_save_meta_box' );
	
	// Custom Meta Box Form
	echo '<p>Price: <input type="text" name="zz_price" value="'.esc_attr( $zz_price ).'" size="10" /></p>';
	echo '<p>Plan:
		<select name="zz_plan" id="zz_plan">
			<option value="daily" '. selected( $zz_plan, 'daily', false ). '>Daily</option>
			<option value="weekly" '. selected( $zz_plan, 'weekly', false ). '>Weekly</option>
			<option value="monthly" '	. selected( $zz_plan, 'monthly', false ). '>Monthly	</option>
			<option value="yearly" '	. selected( $zz_plan, 'yearly', false ). '>Yearly </option>
		</select>
	</p>';
}
 
/**
 * Save meta box content.
 *
 * @param int $post_id Post ID
 */
function zz_save_meta_box( $post_id ) {
    // Save logic goes here. Don't forget to include nonce checks!
	// process form data if $_POST is set
		if( isset( $_POST['zz_plan'] ) ) {
		// if auto saving skip saving our meta box data
		if ( defined( 'DOING_AUTOSAVE' ) && DOING_AUTOSAVE )
			return;
		
		//check nonce for security
		check_admin_referer( plugin_basename( __FILE__ ), 'zz_save_meta_box' );
		
		// save the meta box data as post meta using the post ID as a unique prefix
		update_post_meta( $post_id, '_zz_plan',	sanitize_text_field( $_POST['zz_plan'] ) );
		update_post_meta( $post_id, '_zz_price', sanitize_text_field ( $_POST['zz_price'] ) );
	}
}
add_action( 'save_post', 'zz_save_meta_box' );

How To Use Escape and require / include in WordPress Theme

After get experiment to upload free theme in wordpress.org here some notes which i think need attention in wordpress theme code. You need to know escape and requre_once replacement. Here is the notes :

ESCAPE

Any numeric variable used anywhere

echo int( $int );

Depending on whether it is an integer or a float, (int), absint(), (float) are all correct and acceptable. At times, number_format() or number_format_i18n() might be more appropriate.

Variable within HTML attribute ( esc_attr )

echo '<div id="', esc_attr( $prefix . '-box' . $id ), '">';

Variable URL within HTML attribute

echo '<a href="', esc_url( $url ), '">';

Passing variable to javascript via wp_localize_script()

// No escaping needed in wp_localize_script, WP will escape this.
wp_localize_script( 'your-js-handle', 'variable_name',
	array(
		'prefix_nonce' => wp_create_nonce( 'plugin-name' ),
		'ajaxurl'      => admin_url( 'admin-ajax.php' ),
		'errorMsg'     => __( 'An error occurred', 'plugin-name' ),
	)
);

Variable within javascript block

<script type="text/javascript">
    var myVar = <?php echo esc_js( $my_var ); ?>
</script>

Variable within inline javascript

<a href="#" onclick="do_something(<?php echo esc_js( $var ); ?>); return false;">
<a href="#" data-json="<?php echo esc_js ( $var ); ?>">

$var should be escaped with esc_js(), json_encode() or wp_json_encode().

Variable within HTML textarea

echo '<textarea>', esc_textarea( $data ), '</textarea>';

Variable within HTML tags

echo '<div>', wp_kses_post( $phrase ) , '</div>';

This depends on whether $phrase is expected to contain HTML or not.

  • If not, use esc_html() or any of its variants.
  • If HTML is expected, use wp_kses_post(), wp_kses_allowed_html() or wp_kses() with a set of HTML tags you want to allow.

Variable string within XML or XSL context

echo '<loc>', ent2ncr( $var ), '</loc>';

REQUIRE_ONCE / INCLUDE

require in theme folder
for example you have something like this :

require get_template_directory() . '/inc/my-functions.php';

you can change it to :

get_template_part(inc/my-functions);

require outsite theme folder

for example you have something like this :

require ABSPATH . WPINC . '/class-wp-editor.php';

you can change it to :

load_template( ABSPATH . WPINC . '/class-wp-editor.php' );

How To Make Your WordPress Website Load Faster

To make your website load faster if you are using wordpress here is some checklists which you need to know

  • Choose good website hosting (website server) and which is suitable for your needs. Why you must choose good hosting ? Because website hosting can determine your website loading. If you want to make website for shopping, it has different need when you want to make website for blogging
  • Choose minimalist theme for fast response. Multipurpose theme ussually has a lot resources which need to be loaded. Because it has many purpose functions , css and javascripts files. Choose theme which is specific for your needs. Anyway you don’t need all the functions.
  • Don’t use too many plugins. I think , the ideal plugins should be less than 6. If you use too many , it will slow your website
  • Compress your javascript , css and images.
  • Always update your theme and plugin so suitable with your WordPress version
  • Use CDN
  • Using caching plugins like w3 total cache
  • Deactivate Trackback and Pingback
  • Delete Old Revision Post. You can use revision control plugin