联系人表单插件的wordpress快捷代码不起作用

我制作了我的第一个WP插件，它是一个联系人表单-这是代码：

<?php
/*
Plugin Name: Example Contact Form Plugin
Plugin URI: http://example.com
Description: Simple non-bloated WordPress Contact Form
Version: 1.0
Author: Agbonghama Collins
Author URI: http://w3guy.com
*/
function html_form_code() {
    echo '<form action="' . esc_url( $_SERVER['REQUEST_URI'] ) . '" method="post">';
    echo '<p>';
    echo 'Your Name (required) <br />';
    echo '<input type="text" name="cf-name" pattern="[a-zA-Z0-9 ]+" value="' . ( isset( $_POST["cf-name"] ) ? esc_attr( $_POST["cf-name"] ) : '' ) . '" size="40" />';
    echo '</p>';
    echo '<p>';
    echo 'Your Email (required) <br />';
    echo '<input type="email" name="cf-email" value="' . ( isset( $_POST["cf-email"] ) ? esc_attr( $_POST["cf-email"] ) : '' ) . '" size="40" />';
    echo '</p>';
    echo '<p>';
    echo 'Subject (required) <br />';
    echo '<input type="text" name="cf-subject" pattern="[a-zA-Z ]+" value="' . ( isset( $_POST["cf-subject"] ) ? esc_attr( $_POST["cf-subject"] ) : '' ) . '" size="40" />';
    echo '</p>';
    echo '<p>';
    echo 'Your Message (required) <br />';
    echo '<textarea rows="10" cols="35" name="cf-message">' . ( isset( $_POST["cf-message"] ) ? esc_attr( $_POST["cf-message"] ) : '' ) . '</textarea>';
    echo '</p>';
    echo '<p><input type="submit" name="cf-submitted" value="Send"/></p>';
    echo '</form>';
}
function deliver_mail() {
    // if the submit button is clicked, send the email
    if ( isset( $_POST['cf-submitted'] ) ) {
        // sanitize form values
        $name    = sanitize_text_field( $_POST["cf-name"] );
        $email   = sanitize_email( $_POST["cf-email"] );
        $subject = sanitize_text_field( $_POST["cf-subject"] );
        $message = esc_textarea( $_POST["cf-message"] );
        // get the blog administrator's email address
        $to = get_option( 'admin_email' );
        $headers = "From: $name <$email>" . "'r'n";
        // If email has been process for sending, display a success message
        if ( wp_mail( $to, $subject, $message, $headers ) ) {
            echo '<div>';
            echo '<p>Thanks for contacting me, expect a response soon.</p>';
            echo '</div>';
        } else {
            echo 'An unexpected error occurred';
        }
    }
}
function cf_shortcode() {
    ob_start();
    deliver_mail();
    html_form_code();
    return ob_get_clean();
}
add_shortcode( 'contact_form', 'cf_shortcode' );
?>

这是我用来制作的教程。

当我把[contact_form]放在帖子或页面上时，什么都不会出现。。。无联系表格。

为什么表格不出现？