admin-ajax.php 是WordPress的一部分AJAX API, 是的，它确实处理来自后端和前端的请求。以下是我对你的问题的理解：

2） 如何管理ajax。php工作？

对于logic 你可以参观这里。

这假设您已经知道如何将JavaScript等排入队列。

JavaScript Piece:

jQuery(document).ready(function($) {

    // We\'ll pass this variable to the PHP function example_ajax_request
    var fruit = \'Banana\';

    // This does the ajax request
    $.ajax({
        url: ajaxurl,
        data: {
            \'action\':\'example_ajax_request\',
            \'fruit\' : fruit
        },
        success:function(data) {
            // This outputs the result of the ajax request
            console.log(data);
        },
        error: function(errorThrown){
            console.log(errorThrown);
        }
    });   

});

PHP Piece:

function example_ajax_request() {

    // The $_REQUEST contains all the data sent via ajax 
    if ( isset($_REQUEST) ) {

        $fruit = $_REQUEST[\'fruit\'];

        // Let\'s take the data that was sent and do something with it
        if ( $fruit == \'Banana\' ) {
            $fruit = \'Apple\';
        }

        // Now we\'ll return it to the javascript function
        // Anything outputted will be returned in the response
        echo $fruit;

        // If you\'re debugging, it might be useful to see what was sent in the $_REQUEST
        // print_r($_REQUEST);

    }

    // Always die in functions echoing ajax content
   die();
}

add_action( \'wp_ajax_example_ajax_request\', \'example_ajax_request\' );

// If you wanted to also use the function for non-logged in users (in a theme for example)
 add_action( \'wp_ajax_nopriv_example_ajax_request\', \'example_ajax_request\' );

1）为什么要使用管理ajax。php，而不是在单独的文件（如主题/示例/json）中编码json。php并在那里对数据进行编码？

这可能会有帮助。admin-ajax.php vs Custom Page Template for Ajax Requests