我制作了我的第一个WP插件，它是一个联系表单-下面是代码：

<?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\' );
?>

当我把[contact_form] 在帖子或页面上，没有显示任何内容。。。无联系方式。

为什么表单不会出现？