How to save custom meta box's data? - php

Question

I'm trying to learn something about WordPress plug-in development. Here is my first attemp to write something. This should create an input field on "page" pages to store a custom value.
This is the code I written, but something doesn't work. I can't save my data.
<?php
/*
Plugin Name: nw_Page_Gallery
*/
class nw_Page_Gallery {
public function __construct(){
$this->add_meta_boxes();
}
public function add_meta_boxes(){
add_action("add_meta_boxes", array($this, "add_meta_box_images"));
}
public function add_meta_box_images(){
add_meta_box("nw_page_image", "Sfondo pagina", array($this, "add_image_box"), "page");
}
public function add_image_box($post){
$back_url = get_post_meta($post->ID, 'nw_page_image', true);
echo "Il valore è".$back_url;
?>
<label>Lenght:</label>
<input type="text" class="widefat" name="nw_page_image" id="nw_page_image" value="<?php echo $back_url; ?>" />
<?php
add_action("save_post", function($id){
if(isset($_POST['nw_page_image'])){
update_post_meta(
$id,
'nw_page_image',
strip_tags($_POST['nw_page_image'])
);
}
});
}
}
add_action("admin_init", function(){
$PG = new nw_Page_Gallery();
});
Can someone tells me what is wrong?

Answer 1

You are doing your add_action("save_post", in the last place it should be...
That belongs to the __construct, or as you're doing:
public function add_meta_boxes(){
add_action("add_meta_boxes", array($this, "add_meta_box_images"));
add_action("save_post", function($id){
if(isset($_POST['nw_page_image'])){
update_post_meta(
$id,
'nw_page_image',
strip_tags($_POST['nw_page_image'])
);
}
});
}
Note that you are hooking into save_post without checking for a bunch of things (if it is revision, if doing autosave) and more problematic, without security checks: wp_nonce_field.
You can find plenty of good examples at WordPress Answers, check this search query.