Frequently Used WordPress Action Hooks For Plugin Development

Hooks, Actions and Filters
Hooks are provided by WordPress to allow your plugin to 'hook into' the rest of WordPress; that is, to call functions in your plugin at specific times, and thereby set your plugin in motion. There are two kinds of hooks:

1. Actions
2. Filters

You can see many WordPress action hooks when you are developing a plugin for WordPress, but some WordPress hooks are used more than other hooks. So for developing a plugin, you should have some knowledge of these hooks

plugins_loaded 

This one is the most important hook in any plugin development process. plugins_loaded is fired after all the WordPress files are loaded on the page but before the pluggable functions, then WordPress starts executing everything. So now you can understand, no code snippet will run until this hook is fired

<?php
add_action('plugins_loaded', 'display_my_msg');

function display_my_msg() {
add_action('wp_footer', 'display_message', 100);
}

function display_message() {
echo 'This is dummy Text';
}

?>

init

This hook is fired after everything is set up in WordPress. WordPress also tries to add a plenty of things, for example, registration of taxanomies, initialization of the default widgets and post types. You can say that everything is ready when it will come to this hook, so your plugin whatever you are developing will perhaps use init hook for anything it needs to do, when entire information of WordPress is available to use.

<?php
add_action('init', 'excerpts_to_page_type');

function excerpts_to_page_type() {
add_post_type_support('page', array('excerpt'));
}
?>

wp_head

You can see the difference with and without using wp_head in your template. Without this hook you will not see anything besides your own written code, but with this hook you will see extra files like javascript, css etc after your written code in the head section.

<?php
add_action('wp_head', 'tr_add_meta_desc');

function tr_add_meta_desc() {
//Getting the blog description
$desc = esc_attr(get_bloginfo('description'));
}

//Check meta description is set or not
if(!empty($desc)) {
echo '<meta name="description" content="' . $desc . '" />';
}
?>

template_redirect

The importance of this hook is that at this point WordPress knows which page or post a visitor is viewing. It is just executed before the theme is chosen for the particular page view. template_redirect doesn’t fire in the admin area, it just fired only on the front side. The hook is very useful if you want to load a specific piece of code only for certain page views.

<?php
add_action('template_redirect', 'add_my_css_file');

function add_my_css_file() {

if(is_singular('post')) {
wp_enque_style('add_css', 'my_custom.css', false, 0.1, 'screen');

}
}
?>

admin_menu

admin_menu hook is just for admin pages when page loads. If your plugin doesn’t need to execute in the front end, you can use this hook because whenever your plugin works directly in the admin side, you would absolutely use admin_menu to run your code.

<?php
add_action('admin_menu' , 'my_plugin_page');

function my_plugin_page() {

add_options_page('My Page', 'My Page', 'manage_options', 'my_plugin', 'my_plugin_page");

}
?>