Call to undefined function add_action() - plugins

Question

I am developing a plugin for custom registration form.I have first file customapplicationform.php file , other files in side registration and shortcode folder.
So, My Plugin Directory structure like this :
--->customapplicationform
|--js
|--ajax-registration.js
|--registration
|--registration.php
|--regsubmit.php
|--scripts.php
|--shortcode
|--display.php
|--shortcodes.php
--customapplicatioform.php
It's give error :
Fatal error: Call to undefined function add_action() in E:\xampp\htdocs\aism\wp-content\plugins\customapplicationform\registration\scripts.php on line 17
Please , Tell me what is the problem with this ? and if there any better way than suggest me. Thanks in advance.
1) This is my customapplicationform.php file.
require_once(ABSPATH.'wp-admin/includes/plugin.php');
ob_start();
global $app_db_version;
$app_db_version = '1.0';
function app_install() {
global $wpdb;
global $app_db_version;
$table_name = $wpdb->prefix .'registeration';
$charset_collate = $wpdb->get_charset_collate();
$sql = "CREATE TABLE $table_name (
regid mediumint(9) NOT NULL AUTO_INCREMENT,
time datetime DEFAULT '0000-00-00 00:00:00' NOT NULL,
fname varchar(50) NOT NULL,
lname varchar(50) NOT NULL,
email varchar(50) NOT NULL,
phno int(12) NOT NULL,
PRIMARY KEY(regid)
) ";
require_once( ABSPATH . 'wp-admin/includes/upgrade.php' );
dbDelta( $sql );
add_option( 'app_db_version', $app_db_version );
}
register_activation_hook( __FILE__, 'app_install');
include_once('/shortcode/shortcodes.php');
2) This is my shortcodes.php file.
function shortcode_function( $atts ) {
$plugin_dir_path = dirname(__FILE__);
include_once('display.php');
$data = ob_get_clean();
return $data;
}
add_shortcode( 'custom-application', 'shortcode_function' );
3) This is my display.php file.
include_once(''.dirname(dirname(__FILE__)).'/registration/registration.php');
4) This is my registration.php file.
<form action="<?php echo plugins_url();>/customapplicationform/registration/regsubmit.php" method="Post">
<label>First Name:</label>
<input type="text" name="appfname" id="appfname" />
<label>Last Name :</label>
<input type="text" name="applname" id="applname" />
<label>Email :</label>
<input type="email" name="appemail" id="appemail" />
<label>Phone :</label>
<input type="tel" name="appphone" id="appphone" />
<?php// wp_nonce_field('app_new_user','app_new_user_nonce', true, true ); ?>
<input type="Submit" value="Submit" id="btn-new-user">
</form>
5) This is my regsubmit.php file.
require_once('scripts.php');
// Verify nonce
if( ! wp_verify_nonce( $_POST['app_new_user_nonce'], 'app_new_user' ) )
{
die( 'Ooops, something went wrong, please try again later.' );
}
else {
if(isset($_POST['appemail'])) {
// Post values
echo $fname = $_POST['appfname'];
echo $lname = $_POST['applname'];
echo $email = $_POST['appemail'];
echo $phone = $_POST['appphone'];
$userdata = array(
'fname' => $fname,
'lname' => $lname,
'email' => $email,
'phno' => $phone,
);
$user_id = wp_insert_user( $userdata ) ;
// Return
if( !is_wp_error($user_id) ) {
echo '1';
} else {
echo $user_id->get_error_message();
}
}
}
6) This is my scripts.php file .
function app_register_user_scripts() {
// Enqueue script
wp_register_script('app_reg_script', dirname(__FILE__). '/js/ajax- registration.js', array('jquery'), null, false);
wp_enqueue_script('app_reg_script');
wp_localize_script( 'app_reg_script', 'app_reg_vars', array('app_ajax_url' => admin_url( 'admin-ajax.php' )));
}
add_action('wp_enqueue_scripts', 'app_register_user_scripts');

Answer 1

It's a core function and available if your code is activated trough WordPress and accessed trough WordPress. If you try to call your plugin file outside the WordPress scope (for example you approach the file from the browser, directly) then add_action is not available unless you require wp-load.php at the top of your file from the WordPress root.

Answer 2

Since we're calling core functions before $wp->init; we need to include pluggable.php
require_once(ABSPATH .'wp-includes/pluggable.php');