您的代码中有许多错误和错误做法。大部分我都修好了。在这里解释所有这些是不可能的。我已经在他们需要的地方写了解释作为评论。请仔细阅读整个代码和注释-

custom.js

// Wrap any jQuery code like this. It makes \'$\' use fullproof
// and prevent also some other error.
(function($){
    // And always use \'use strict\' to make your JavaScript code mode strict.
    \'use strict\';
    // Wrap it with after the DOM is ready block.
    $(function (e) {
        // Try not to use click() method directly.
        // Rather try to delegate the event with on() method.
        $(\'.get_project\').on( \'click\', function(e) {
            e.preventDefault();
            var postid = $(this).attr(\'data-postid\');
            console.log(postid);
            // I don\'t know why the shorthand method had not worked for me as well
            // But this method has worked for me.
            $.ajax({
                type: "POST",
                url: my_ajax_object.ajax_url,
                data: {
                    action: \'my_load_ajax_content\',
                    postid: postid,
                }
            }).done(function (data) {
                // Just simple html() method with data will show all the content.
                $(\'.TARGETDIV\').html(data);
            });
        });
    });
})(jQuery);

functions.php

function my_load_ajax_content () {
    // You need to grab the data from $_POST variable
    // And must sanitize the data.
    $pid = intval($_POST[\'postid\']);
    $the_query  = new WP_Query(array(\'p\' => $pid));

    if ($the_query->have_posts()) {
        while ( $the_query->have_posts() ) {
            $the_query->the_post();
            $data = \'
            <div class="post-container">
                <div id="project-content">
                    <h1 class="entry-title">\' . get_the_title() . \'</h1>
                    <div class="entry-content">\' . get_the_content() . \'</div>
                </div>
            </div>  
            \';
        }
    }
    else {
        // Since you\'re declared the $data variable before then assign the next value also in $data
        // And at the end just echo it.
        $data = \'<div id="postdata">\'.__(\'Didnt find anything\', THEME_NAME).\'</div>\';
    }
    wp_reset_postdata();

    echo \'<div id="postdata">\'. $data .\'</div>\';
    // And must die() the function
    die();
}
// The actual hook is wp_ajax_noprive_{$action} and wp_ajax_{$action}
// You action is my_load_ajax_content in JS. So your hook will be
add_action ( \'wp_ajax_nopriv_my_load_ajax_content\', \'my_load_ajax_content\' );
add_action ( \'wp_ajax_my_load_ajax_content\', \'my_load_ajax_content\' );

function my_enqueue() {
    // First register script
    wp_register_script( \'ajax-script\', get_template_directory_uri() . \'/js/custom.js\', array(\'jquery\') );
    // Localize script
    wp_localize_script( \'ajax-script\', \'my_ajax_object\',
        array( \'ajax_url\' => admin_url( \'admin-ajax.php\' ) )
    );
    // Then enqueue script
    wp_enqueue_script( \'ajax-script\' );
}

add_action( \'wp_enqueue_scripts\', \'my_enqueue\' );