Question: Most solutions I found are for front-end use. This is for a plugin, so the all activity is in the back-end.

How do I get the page ID that's being currently use(edited) in the admin?

**Note** I'm out of the loop. I just need to get the ID of page(not posts) that I'm currently seeing in the back-end.

Answer: 
You can also use

```
$post_id = $_GET['post'];

```

Or you can use a hook (probably better).

```
function id_WPSE_114111() {
    global $post;
    $id = $post->ID;
    // do something
}

add_action( 'admin_notices', 'id_WPSE_114111' );

```

You will need to add a conditional since this will run on all admin pages, I recommend using `get_current_screen();`

For example to run only on *pages*:

```
function id_WPSE_114111() {

    global $my_admin_page;
    $screen = get_current_screen();

    if ( is_admin() && ($screen->id == 'page') ) {
        global $post;
        $id = $post->ID;
        var_dump($id);
    }
}

add_action( 'admin_notices', 'id_WPSE_114111' );

```
You just use this code in the **functions.php** file, It will give you a current edit page or post ID

```
function get_the_current_page_id(){
$post_id = null;
if( isset( $_REQUEST['post']) || isset($_REQUEST['post_ID'] ) ){
    $post_id = empty( $_REQUEST['post_ID'] ) ? $_REQUEST['post'] : $_REQUEST['post_ID' ];
}

//print_r($post_id) For check
//die();
}

//get_the_current_page_id() //Call the function

```