管理画面に更新日枠を追加する

init.php

管理画面css読み込み

//***--- 管理画面用JSとCSS読み込み　true=body直前 false=head
//my_admin_script.jsはテーマファイル内/js/にアップロード
//my_admin_style.cssはテーマファイル内/css/にアップロード
function my_admin_script(){
    wp_enqueue_script( 'my_admin_script', get_template_directory_uri().'/js/my_admin_script.js', array('jquery'), '', true);
    wp_enqueue_style('admin-styles', get_template_directory_uri().'/css/my_admin_style.css');
}
add_action( 'admin_enqueue_scripts', 'my_admin_script' );

my_admin_style.css

.modified-box {
    padding-top: 5px;
    overflow: hidden;
}
.modified-box-date {
    font-weight: bold;
}
.modified-time-timestamp-wrap {
    margin-bottom: 15px;
}
.modified-time {
    margin-top: 5px; 
    padding: 2px 0 1px 0;
    display: block !important;
    height: auto !important;
}
.modified-time:before { 
    font: normal 20px/1 'dashicons'; 
    content: '\f145'; 
    color: #888; 
    padding: 0 5px 0 0; 
    top: -1px; 
    left: -1px; 
    position: relative; 
    vertical-align: top; 
}
select.mm { 
    height: 21px; 
    line-height: 14px; 
    padding: 0; 
    vertical-align: top;
    font-size: 12px;
}
#aa_mod, #jj_mod, #hh_mod, #mn_mod { 
    padding: 1px; 
    font-size: 12px; 
}
#jj_mod, #hh_mod, #mn_mod { 
    width: 2em; 
}
#aa_mod { 
    width: 3.4em;
}

custom-post.php

//***--- ブログ管理画面の「公開」の上に「更新日時」枠を追加

// メタボックスを表示　メタボックス内のソースはmy_custom_mod_dateで設定
if( !function_exists( 'my_add_meta_box' ) ):
    function my_add_meta_box() {
        add_meta_box( 'update_level', '更新日時', 'my_custom_mod_date', 'post', 'side', 'default' );
    }
    add_action( 'admin_menu', 'my_add_meta_box' );
    endif;
    
    // 更新日フォーム
    if( !function_exists( 'my_custom_mod_date' )):
    function my_custom_mod_date() {
        global $post;
    ?>
    <div class="modified-box">    
    <input id="update_level_edit" name="update_level" type="radio" value="edit" checked="checked" />手動で設定
    <?php
        if( get_the_modified_date( 'c' ) ) {
            $stamp = '更新日時: <span class="modified-box-date">' . get_the_modified_date( __( 'M j, Y @ H:i' ) ) . '</span>';
        }
        else {
            $stamp = '更新日時: <span class="modified-box-date">未更新</span>';
        }
        $date = date_i18n( get_option('date_format') . ' @ ' . get_option('time_format'), strtotime( $post->post_modified ) );
    ?>
    <span class="modified-time"><?php printf( $stamp, $date ); ?></span>
    <div class="modified-time-timestamp-wrap" onkeydown="document.querySelector('#update_level_edit').checked=true" onclick="document.querySelector('#update_level_edit').checked=true">
    <?php my_time_mod_form(); ?>
    </div>
    <div><input name="update_level" type="radio" value="update"/>現在の日付に更新</div>
    </div>
    <?php
    }
    endif;
    
    //更新日時変更の入力フォーム
    if( !function_exists( 'my_time_mod_form' ) ):
    function my_time_mod_form() {
        global $wp_locale, $post;
    
        $tab_index = 0;
        $tab_index_attribute = '';
        if ( (int) $tab_index > 0 ) {
            $tab_index_attribute = ' tabindex="' . $tab_index . '"';
        }
        //mysql2date = phpのdate()が受け付ける書式に変換
        $jj_mod = mysql2date( 'd', $post->post_modified, false );
        $mm_mod = mysql2date( 'm', $post->post_modified, false );
        $aa_mod = mysql2date( 'Y', $post->post_modified, false );
        $hh_mod = mysql2date( 'H', $post->post_modified, false );
        $mn_mod = mysql2date( 'i', $post->post_modified, false );
        $ss_mod = mysql2date( 's', $post->post_modified, false );
    
        $year = '<label for="aa_mod" class="screen-reader-text">年' .
            '</label><input type="text" id="aa_mod" name="aa_mod" value="' .
            $aa_mod . '" size="4" maxlength="4"' . $tab_index_attribute . ' autocomplete="off" />年';
    
        $month = '<label for="mm_mod" class="screen-reader-text">月' .
            '</label><select id="mm_mod" class="mm" name="mm_mod"' . $tab_index_attribute . ">\n";
        for( $i = 1; $i < 13; $i = $i +1 ) {
            $monthnum = zeroise($i, 2);
            $month .= "\t\t\t" . '<option value="' . $monthnum . '" ' . selected( $monthnum, $mm_mod, false ) . '>';
            $month .= $wp_locale->get_month_abbrev( $wp_locale->get_month( $i ) );
            $month .= "</option>\n";
        }
        $month .= '</select>';
    
        $day = '<label for="jj_mod" class="screen-reader-text">日' .
            '</label><input type="text" id="jj_mod" name="jj_mod" value="' .
            $jj_mod . '" size="2" maxlength="2"' . $tab_index_attribute . ' autocomplete="off" />日';
        $hour = '<label for="hh_mod" class="screen-reader-text">時' .
            '</label><input type="text" id="hh_mod" name="hh_mod" value="' . $hh_mod .
            '" size="2" maxlength="2"' . $tab_index_attribute . ' autocomplete="off" />';
        $minute = '<label for="mn_mod" class="screen-reader-text">分' .
            '</label><input type="text" id="mn_mod" name="mn_mod" value="' . $mn_mod .
            '" size="2" maxlength="2"' . $tab_index_attribute . ' autocomplete="off" />';
    
        printf( '%1$s %2$s %3$s @ %4$s : %5$s', $year, $month, $day, $hour, $minute );
        echo '<input type="hidden" id="ss_mod" name="ss_mod" value="' . $ss_mod . '" />';
    }
    endif;
    
    // それぞれの更新日時に変更する */
    if( !function_exists( 'my_insert_post_data' )):
    function my_insert_post_data( $data, $postarr ){
        $mydata = isset( $_POST['update_level'] ) ? $_POST['update_level'] : null;
    
        if( $mydata === 'edit' ) {
            $aa_mod = $_POST['aa_mod'] <= 0 ? date('Y') : $_POST['aa_mod'];
            $mm_mod = $_POST['mm_mod'] <= 0 ? date('n') : $_POST['mm_mod'];
            $jj_mod = $_POST['jj_mod'] > 31 ? 31 : $_POST['jj_mod'];
            $jj_mod = $jj_mod <= 0 ? date('j') : $jj_mod;
            $hh_mod = $_POST['hh_mod'] > 23 ? $_POST['hh_mod'] -24 : $_POST['hh_mod'];
            $mn_mod = $_POST['mn_mod'] > 59 ? $_POST['mn_mod'] -60 : $_POST['mn_mod'];
            $ss_mod = $_POST['ss_mod'] > 59 ? $_POST['ss_mod'] -60 : $_POST['ss_mod'];
            $modified_date = sprintf( '%04d-%02d-%02d %02d:%02d:%02d', $aa_mod, $mm_mod, $jj_mod, $hh_mod, $mn_mod, $ss_mod );
            if ( ! wp_checkdate( $mm_mod, $jj_mod, $aa_mod, $modified_date ) ) {
                unset( $data['post_modified'] );
                unset( $data['post_modified_gmt'] );
                return $data;
            }
            $data['post_modified'] = $modified_date;
            $data['post_modified_gmt'] = get_gmt_from_date( $modified_date );
        }

        return $data;
    }
    add_filter( 'wp_insert_post_data', 'my_insert_post_data', 10, 2 );
    endif;