get_post_meta giving errors while creating a metabox

Question

i was following atutorial on how to make a custom metabox to wordpress post but its giving errors

here is my full code

//Add Metabox
function diwp_custom_metabox(){
    //add_meta_box(metabox_id,metabox name,callback function,metabox location(page,post,custom post etc),context-(normal,side,advanced),piority())
    add_meta_box('diwp-metabox','My Custom Metabox','diwp_post_metabox_callback','post','normal');
}

//add action
add_action('add_meta_boxes','diwp_custom_metabox');
//metabox callback function

function diwp_post_metabox_callback(){
    // echo 'hi i am diwp metabox';
    ?>
    <div class="row">
      <div class="label">Post Reading Time</div>
      <div class="fields">
        <input type="text" name="_diwp_reading_time" value="<?php get_post_meta($post->ID,'post_reading_time',true); ?>">
      </div>
    </div>
    <?php
}

function diwp_save_custom_metabox(){
    // update_post_meta($post_id,$meta_key,$meta_value,$prev_value);
    global $post;
    if(isset($_POST['_diwp_reading_time'])){
        update_post_meta($post->ID,'post_reading_time',$_POST['_diwp_reading_time']);
    }
}

add_action('save_post','diwp_save_custom_metabox');

error screen shot

any help will be appreciated ,thanks

Answer 1

The error there clearly says that there's an undefined variable (post) in your metabox callback function.

So you need to define $post in your function head:

// The $post variable is passed by WordPress.
function diwp_post_metabox_callback( $post )

And you should also do the same to diwp_save_custom_metabox() function (which is hooked to save_post):

// Here, $post is the second parameter.
function diwp_save_custom_metabox( $post_ID, $post ) {
    // ...
}

// Don't forget to set the 4th parameter to 2:
add_action( 'save_post', 'diwp_save_custom_metabox', 10, 2 );

Or alternatively, use get_post() and not the global call:

// Here, $post is the second parameter.
function diwp_save_custom_metabox( $post_ID ) {
    $post = get_post( $post_ID ); // like this
//  global $post;                 // not this

    // ...
}

add_action( 'save_post', 'diwp_save_custom_metabox' );