get the modified date of post meta box - php

Question

i'm searching for a way to display the modified date of a custom field / meta box. until now, i only know how to echo
the_modified_date('l, j.n.Y');
but this one only works with the entire post.
i'am using a meta_box for additional pdf files uploading, code:
<?php class PDF_Metabox_id1 {
function __construct() {
add_action( 'post_mime_types', array( $this, 'pdf_mime_type_id1' ) );
add_action( 'add_meta_boxes', array( $this, 'admin_scripts_id1' ), 5 );
add_action( 'add_meta_boxes', array( $this, 'metabox_add_id1' ) );
add_action( 'save_post', array( $this, 'pdf_save_postdata_id1') );
add_action( 'wp_ajax_refresh_pdf', array( $this, 'refresh_pdf_id1' ) ); }
function pdf_mime_type_id1() {
$post_mime_types['application/pdf'] = array( __( 'PDFs' ), __( 'Manage PDFs' ), _n_noop( 'PDF <span class="count">(%s)</span>', 'PDFs <span class="count">(%s)</span>' ) );
return $post_mime_types;
}
function admin_scripts_id1() {
wp_register_script( 'pdf_metabox_js', get_stylesheet_directory_uri() . '/js/pdf_metabox.js' );
}
function metabox_add_id1() {
$post_types = array( 'myposttype','anotherposttype' );
$context = 'normal'; $priority = 'low';
foreach( $post_types as $post_type ) {
add_meta_box( 'pdf_metabox_id1', __( 'PDF Box 1', 'pdf_metabox_id1' ), array( $this, 'pdf_metabox_id1' ), $post_type, $context, $priority );
wp_enqueue_media();
wp_enqueue_script( 'pdf_metabox_js' );
}
}
function pdf_metabox_id1( $post ) {
$original_post = $post; echo $this->pdf_metabox_html_id1( $post->ID ); $post = $original_post;
}
function pdf_item_id1( $id ) {
if(!$id) return; $pdf_url = esc_url_raw(wp_get_attachment_url($id)); $pdf = $pdf_url; return $pdf;
}
function pdf_metabox_html_id1( $post_id ) {
$current_value = ''; $post_meta = get_post_custom($post_id);
if( isset($post_meta['pdf_id_id1'][0] ) ) $current_value = $post_meta['pdf_id_id1'][0];
$return = ''; wp_nonce_field( plugin_basename( __FILE__ ), 'pdf_noncename' );
$return .= '<p>';
$return .= '<a title="'.__( 'PDF', 'pdf_metabox_id1' ).'" class="button button-primary insert-pdf-button" id="insert_pdf_button_id1" href="#" style="float:left">'.__( 'Upload / editiere PDF', 'pdf_metabox_id1' ).'</a><span id="pdf_spinner_id1" class="spinner" style="float:left"></span></p>';
$return .= '<div style="clear:both"></div>';
$return .= '<input type="hidden" name="pdf_id_id1" id="pdf_id_id1" value="'.$current_value.'">';
$return .= '<div style="clear:both"></div>';
$return .= '<div id="pdf_wrapper_id1">';
$pdf = $this->pdf_item_id1( $current_value ); if( empty( $pdf ) ) {
$return .= '<p>Diesem Feld ist kein PDF hinterlegt.</p>'; } else {
$return .= '<br />URL des PDF:<br /> ';
$return .= $pdf; }
$return .= '</div>';
return $return;
}
function pdf_save_postdata_id1($post_id){
if ( isset($_POST['post_type']) && 'post' == $_POST['post_type'] ) {
if ( !current_user_can( 'edit_post', $post_id ) ) return; } if ( !isset( $_POST['pdf_noncename'] ) || ! wp_verify_nonce( $_POST['pdf_noncename'], plugin_basename( __FILE__ ) ) ) return;
if(isset($_POST['pdf_id_id1']) ): update_post_meta($post_id, 'pdf_id_id1', sanitize_text_field( $_POST['pdf_id_id1'] ) );
else: if (isset($post_id)) {
delete_post_meta($post_id, 'pdf_id_id1'); }
endif;
}
function refresh_pdf_id1() {
if(isset($_POST['id'])){
$item = $_POST['id'];
if($item != '' && $item !=0){
$pdf = $this->pdf_item_id1( $item );
$ret = array();
if( !empty( $pdf ) ) {$ret['success'] = true;
$ret['pdf'] = $pdf; } else {
$ret['success'] = false; } } else {
$ret['success'] = true; $ret['pdf'] = ''; } } else {
$ret['success'] = false; } echo json_encode( $ret ); die();
}
}
$PDF_Metabox_id1 = new PDF_Metabox_id1();
in my theme i'm using:
$post_meta_id1 = get_post_custom(get_the_ID());
$pdf_id_id1 = $post_meta_id1['pdf_id_id1'][0];
$pdf_url_id1 = wp_get_attachment_url($pdf_id_id1);
...and now i want to display the modified date of this field. any ideas?

Answer 1

As per the comment
how do i save the modified date of this custom field and how do i get it?
You may need to check every custom field in loop one by one if any of custom fields doesnot matched with the current post data then save a new custom field to post_meta. then retrieve in your template/page.
Just an idea:
<?php
function attributes_save_postdata( $post_id ) {
$postcustom = get_post_custom( $post_id );
$is_modified = false;
foreach ( $postcustom as $key => $val ) {
var_dump( $val );
// check your post custom values and
$getpostmeta = get_post_meta( $post_id, 'your_meta_key', true );
// if database value ($getpostmeta) not equal to current post value($_POST['your_meta_key'])
if ( $getpostmeta != $_POST['your_meta_key'] ) {
$is_modified = true;
// if found any custom field updated set $modified = true
}
}
// if found any custom field updated add or update new date and time
if ( $is_modified ) {
$date = date( 'Y-m-d h:i:s' ); // example : 2016-02-02 12:00:00 current date and time
update_post_meta( $post_id, '_modifieddate', $date );
}
}
add_action( 'save_post', 'attributes_save_postdata' );
Then in your theme. get modified date.
$post_id = get_the_ID();
$getpostmeta = get_post_meta( $post_id, 'your_meta_key', true );

Answer 2

I think that wordpress built-in function about this would help you out even for the custom fields.
<p>Last modified: <?php the_modified_time(); ?></p>