Wordpress Plugins

Question 1

All plugins belong in..

Answer 1

wp-content/plugins

Question 2

What is required for Wordpress to be able to ‘see’ your plugin?

Answer 2

Meta data in the main PHP file.

Simply add comments with the following fields:

Plugin Name:
Plugin URI:
Description:
Version:
Author:
Author URI:
License:

Question 3

What are the two kinds of hooks?

Answer 3

Filters / Actions

Question 4

What are actions related to?

Answer 4

Wordpress core events

Question 5

What are Filters used for?

Answer 5

The ability to modify posts / variables etc before they are rendered to the screen

Question 6

What class is used to run a query in a plugin?

Answer 6

WP_Query

Question 7

What parameter to WP_Query would ensure the current post is not included as part of the query (i.e. if you wanted to get a list of related posts, but you wanted to exclude the current post from that list)?

Answer 7

‘post_not_in’ => get_the_ID()

Question 8

When you run $loop->the_post(), what ‘type’ of functions are available to access the data for the current post?

Answer 8

template tags. These may have been available already, but by calling the_post, you are updating the values for the current post being processed. This is useful in a loop.

Question 9

If you are able to see a post you have created through the edit screen in the admin edit area, but you can’t access it from the front page. What is the likely problem?

Answer 9

The .htaccess file has not been written correctly.

Question 10

What is the difference in the way you access the posts, between running a query (WP_Query) and just being on the index page?

Answer 10

WHen you run a specific query (i.e. $query = WP_Query()), you will access the posts via the query, i.e. $query->the_post().

If you are just on a page and are iterating through available posts, i.e. while (have_posts()) : the_post(), you can simply use the global versions of these functions.

Question 11

When creating a shortcode, which action do you hook into?

Answer 11

‘init’

add_shortcode(‘sc_name’, ‘shortcodefunction’);

Question 12

There are two parameters that are passed to a shortcode function, what are they?

Answer 12

$args (a list of arguments passed into the shortcode)

$content (the content that can be passed to the shortcode)

Question 13

How do you write the shortcode in a post?

Answer 13

Add this into your editor (it doesn’t have to be in the text pane).

[sc_name param1=’foobar’]My Content[/sc_name]

Where sc_name is the name registered with add_shortcode.

Question 14

Why might you want to use wp_remote_get rather than cURL to obtain data from the web?

Answer 14

Because there is such a wide variety of installations of PHP around the world (with 30% of the internet on WP) - you may find external libraries are not always installed (like cURL).

Question 15

What action/hook would you use to add a metabox to a post?

Answer 15

add_action(‘add_meta_boxes’, ‘functionname’);

Question 16

What function do you use to get the data from a metabox?

Answer 16

get_custom_post ($post->ID);

This will return an array that has indexes corresponding to the ID’s in the form’s HTML.

NOTE: You probably need to import the $post variable from the global scope before using it.

global $post;

Question 17

What action do you use to save data?

Answer 17

add_action(‘save_post’, ‘functionhandler’);

Question 18

Should you use “autosave” when filling in meta data fields?

Answer 18

No. You can prevent this by doing the following check:

if (defined( ‘DOING_AUTOSAVE’) && DOING_AUTOSAVE) {
return;
}

Question 19

What must you check before committing a save for metadata on a post?

Answer 19

You must check that the user has permission to save a post. You can do that by using the following code:

if ( !current_user_can( ‘edit_posts’) ) {
return;
}

Question 20

If you find you are not getting the data in the $_POST variable in the ‘save_post’ action, what is one thing you can check for?

Answer 20

Make sure the input has both an ID and a NAME attribute. Remember, PHP works with NAME attributes.

Question 21

What method is used to actually save the post meta data?

Answer 21

update_post_meta( $post_id, ‘cain_youtube’, esc_url( $_POST[ ‘cain_youtube’ ] ) );

$post_id comes as a parameter from the function (the one that is hooked to the save_post action).

NOTE: In the documentation for this function, it says some of this data should be raw instead of sanatised for database queries. Look into that.

Question 22

What filter would you use to modify the contents of the titles on a post?

Answer 22

add_filter(‘the_title’, ‘myfunc’);

Question 23

What filter would you use to modify the contents of the content on a post?

Answer 23

add_filter(‘the_content’, ‘myfunc’);

Question 24

What filter would you use to modify the list of categories?

Answer 24

add_filter(‘list_cats’, ‘myfunc’);

Question 25

When you are writing a widget, it's important to remember that it's not working in isolation. Someone else may write a plugin that puts all the widget titles in uppercase for instance. How would you make sure your widget / plugin supports that?

Answer 25

You can call the function: apply_filters( 'widget_titles', $instance[ 'title' ] ); 'widget_titles' refers to the filter_hook, so this is how you specify which filters are relevant (obviously, if it's a widget title, you should only use the widget_titles hook).

Question 26

How do you add a new menu to the "settings" tab in wordpress admin?

Answer 26

add_action( 'admin_menu', 'cain_plugin_menu' ); function cain_plugin_menu() { add_options_page( 'Zenva Wishlist Options', 'Zenva Wishlist', 'manage_options', 'cainmenu', 'cain_plugin_options' ); } NOTE: manage_options is a flag to describe the priv. level required to make changes.

Question 27

In order for settings fields to show up, you have to do what first?

Answer 27

Register the settings. ``` add_action( 'admin_init', 'cain_admin_init' ); function cain_admin_init() { register_setting( 'cain-group', 'cain_dashboard_title' ); register_setting( 'cain-group', 'cain_number_of_items' ); } ``` NOTE: This does not actually show the form, it simply allows for the forms to be shown. The first parameter to register_setting is a "group" of settings (an internal thing).

Question 28

In your admin screen, what should you take into account when laying out the form?

Answer 28

You should use the same classes / layout as wordpress, so that styling is consistent, even when they update versions.

Question 29

What function prints a submit button for a form in PHP?

Answer 29

submit_button();

Question 30

In the settings API, where is the data stored in the database?

Answer 30

It is stored in a table called: $prefix_options, where $prefix is the value set in wp-config.php in the variable $table_prefix.

Question 31

What function is responsible for embedding a nonce value (and other meta data for the admin page forms) on the admin pages?

Answer 31

settings_fields( 'page-slug' ); This function will output a number of values that are used by the form for security etc.

Question 32

When using AJAX with plugins, what is the purpose of using the wp_localize_script with AJAX?

Answer 32

The wp_localize_script function is used to inject server side data to the client side, which can then be used, or passed back to the server.

Question 33

When using AJAX with plugins, why do we potentially need to add 'two' actions for the server side processing function?

Answer 33

AJAX has a concept of privileged and non-privileged use. (i.e, are you logged in or not). You have to add one for each case (if you want to support each case).

Question 34

What is unusual about the action name that you use when declaring an AJAX script?

Answer 34

Instead of using a prebuilt action, you create your own action - you have to add the prefixes wp_ajax_ wp_ajax_nopriv_ But remember, when you use the actual action names, you drop those prefixes.

Question 35

Once you've declared the action for an AJAX script, where is that used?

Answer 35

You use it on the client side when specifying the post action.

Question 36

What script processes your AJAX requests on the server side?

Answer 36

admin-ajax.php

Question 37

Rather than give jQuery.post the full url to admin-ajax.php, you can use a predefined variable provided by wordpress. What is that variable?

Answer 37

ajaxurl

Question 38

What function can you use to determine whether the user is logged in?

Answer 38

is_user_logged_in()

Question 39

How do you obtain an object containing the current user?

Answer 39

$user = wp_get_current_user();

Question 40

What function do you use to add meta data to the user?

Answer 40

add_user_meta( $user->ID, 'name_of_field', $data); NOTE: name_of_field is the name of the meta data field that will be stored against the user.

Question 41

How do you retrieve the meta data stored against a user?

Answer 41

$values = get_user_meta( $user_id, 'wanted_posts' );

Question 42

It's best practice to add a what? to the beginning of each meta field name?

Answer 42

Unique prefix.

Question 43

Why do you need to check if a user is logged in before trying to save meta data?

Answer 43

Because you can't save user meta data for someone that is not logged in.

Question 44

What event do you use to create a dashboard widget?

Answer 44

wp_dashboard_setup

Question 45

Why should you use wp_get_current_user instead of get_current_user?

Answer 45

get_current_user gives you your apache user, not the logged in user.

Question 46

What function do you use to actually add the dashboard widget to the screen?

Answer 46

wp_add_dashboard_widget( 'css_id', $title, 'cain_show_dashboard_widget' );

Question 47

What is the gotcha with using wordpress cron jobs?

Answer 47

They are not actually the same as server side cron jobs. When you setup a server side cron job, it's guaranteed to run when requested. But because wordpress/php doesn't run all the time, it will only execute when a request (of any type) is sent to the server.

Question 48

What action would you use to create a cron job?

Answer 48

The 'init' action.

Question 49

In your cronjob initialisation function, what must you do before initialising the cronjob itself?

Answer 49

Make sure it hasn't already been initialised (as we run this code path everytime the server is touched). if ( !wp_next_scheduled( 'cm_sendmail_hook' ) ) { wp_schedule_event( time(), 'hourly', 'cm_sendmail_hook' ); }

Question 50

What does the parameters of 'wp_shedule_event' do?

Answer 50

wp_schedule_event($firsttime, $frequency, $hook, $args) $firsttime - must be unix time stamp, this is the first time it will run - can just pass 'time()' to make it run the very first time $frequency - string specifying frequency 'hourly', 'daily', 'twicedaily' $hook - the function that is to be run. This function must have been registered using add_action, and given a custom hook name.

Question 51

What are the three parts of a plugins lifecycle?

Answer 51

Activation Deactivation Deletion/Removal

Question 52

What should you do on plugin deletion?

Answer 52

Remove all traces of the plugin - all tables, data etc. It's a pretty final step (i.e. the user really wants this).

Question 53

It's common practice to put the uninstall code where?

Answer 53

In an uninstall file, in the plugin directory

Question 54

What function do you call in the plugin activation part of the lifecycle, to perform actions like creating database tables?

Answer 54

register_activation_hook( __FILE__, 'name_of_function' );

Question 55

What function do you call in the plugin deactivation cycle to (for instance) record the fact it has been deactivated to a log file?

Answer 55

register_deactivation_hook ( __FILE__, 'name_of_function' );

Question 56

How do you access the WP database so you can add new tables?

Answer 56

Use the global variable. global $wpdb;

Question 57

How do you 'name' a new table, such that it uses the correct prefix (remember, users can specify their own prefix)?

Answer 57

global $wpdb; $table_name = $wpdb->prefix . 'my_table';

Question 58

How can you check to make sure you haven't already created this table?

Answer 58

if ( $wpdb->get_var("SHOW TABLES LIKE `$table_name`") != $table_name) { // Do stuff }

Question 59

How do you create a table, once you have an SQL statement?

Answer 59

$sql = // sql statement - standard stuff require_once( ABSPATH, 'wp-admin/includes/upgrade.php'); dbDelta( $sql ); NOTE: the WP upgrade.php file is responsible for adding new tables to the database.

Question 60

Database table creation should be done using...

Answer 60

register_activation_hook ( __FILE__, 'my_func_name' );

Question 61

What wp function can be used to get the current time?

Answer 61

current_time()

Question 62

What parameter can be passed to current_time to get the time in a MySQL format?

Answer 62

current_time( 'mysql' );

Question 63

How do you insert data into a wordpress database?

Answer 63

global $wpdb; $tablename = $wpdb->prefix . 'hits'; ``` $newdata = array( 'hit_ip' => $ip, 'hit_date' => current_time('mysql'), 'hit_post_id' => $post_id ); ``` $wpdb->insert( $tablename, $newdata ); NOTE: The column names must match the entries in the array.

Question 64

What is one way of implementing a page counter?

Answer 64

You can check that the page is single (is_single()) and then capture the users IP address and record a page hit in the database. This will give you a total page view count. You can then use the IP address to filter for unique page views.

Question 65

How would you drop a table when your plugin is deleted?

Answer 65

if ( $wpdb->get_var( "SHOW TABLES LIKE '$tablename'" ) == $tablename ) { $sql = "DROP TABLE '$tablename';"; $wpdb->query( $sql ); } NOTE: This will delete your code too (not the sql, the act of deleting a plugin).

Question 66

What must you do before testing the delete plugin functionality?

Answer 66

Backup your code!! | it will delete it