get\\u post（）和get\\u post\\u meta（）应该可以收集数据，而array\\u multisort（）应该能够按升序对数据进行排序。

    // Query the database to get the posts from your post types

    $project_args = array( \'post_type\' => \'projects\', "numberposts" => -1 );
    $task_args = array( \'post_type\' => \'tasks\', "numberposts" => -1 );
    $material_args = array( \'post_type\' => \'materials\', "numberposts" => -1 );

    $projects = get_posts( $project_args );
    $tasks = get_posts( $task_args );
    $materials = get_posts( $material_args );

    $list_items = array();
    $timestamps = array();

    // Loop through each set of posts adding the data you want to an array and their timestamp to another array
    foreach($projects as $project){ 
        array_push( $list_items, array( 
            \'name\' => $project->post_title, 
            \'date\' => get_post_meta( $project->ID, \'custom_date\'),
            )
        ); 
        array_push( $timestamps, strtotime( get_post_meta( $project->ID, \'custom_date\') ) );    
        }

    foreach($tasks as $task){ 
        array_push( $list_items, array( 
            \'name\' => $task-> post_title, 
            \'date\' => get_post_meta( $task->ID, \'custom_date\'),
            )
        ); 
        array_push( $timestamps, strtotime( get_post_meta( $task->ID, \'custom_date\') ) );       
        }

    foreach($materials as $material){ 
        array_push( $list_items, array( 
            \'name\' => $material-> post_title, 
            \'date\' => get_post_meta( $material->ID, \'custom_date\'), 
            )   
        );
        array_push( $timestamps, strtotime( get_post_meta( $material->ID, \'custom_date\') ) );       
        }

    //Sort both arrays based on the timestamp   
    $array_multisort( $timestamps, $list_items );

    //Output as you like
    print_r( $list_items );

对于多个日期，只需向foreach循环中添加额外的元字段，并确保将要排序的日期分配给$timestamps变量。

    foreach($materials as $material){ 
        array_push( $list_items, array( 
            \'name\' => $material-> post_title, 
            \'sort_date\' => get_post_meta( $material->ID, \'sort_date\'),
            \'date_1\' => get_post_meta( $material->ID, \'date_1\'),
            \'date_2\' => get_post_meta( $material->ID, \'date_2\'),
            \'date_3\' => get_post_meta( $material->ID, \'date_3\'), 
            )   
        );
        array_push( $timestamps, strtotime( get_post_meta( $material->ID, \'sort_date\') ) );     
        }