Undefined function error when creating Custom Meta Box

Question

Following this tutorial, I am trying to create a custom Meta Box on my theme by adding following codes to the function.php file:

add_meta_box( 'my-meta-box-id', 'My First Meta Box', 'cd_meta_box_cb', 'post', 'normal', 'high' ); add_action( 'add_meta_boxes', 'cd_meta_box_add' ); function cd_meta_box_add() { add_meta_box( 'my-meta-box-id', 'My First Meta Box', 'cd_meta_box_cb', 'post', 'normal', 'high' ); } function cd_meta_box_cb() { echo 'What you put here, show\'s up in the meta box'; } 

but I am getting following error :

( ! ) Fatal error: Call to undefined function add_meta_box() in C:\wamp\www\TMPress\wp-content\themes\twentytwelve\cpt.php on line 94 Call Stack # Time Memory Function Location 1 0.0012 865440 {main}( ) ..\edit.php:0 2 0.0018 982824 require_once( 'C:\wamp\www\TMPress\wp-admin\admin.php' ) ..\edit.php:10 3 0.0021 1008744 require_once( 'C:\wamp\www\TMPress\wp-load.php' ) ..\admin.php:30 4 0.0023 1026872 require_once( 'C:\wamp\www\TMPress\wp-config.php' ) ..\wp-load.php:29 5 0.0029 1158248 require_once( 'C:\wamp\www\TMPress\wp-settings.php' ) ..\wp-config.php:90 6 0.3251 32951888 include( 'C:\wamp\www\TMPress\wp-content\themes\twentytwelve\functions.php' ) ..\wp-settings.php:291 7 0.3255 32979176 include_once( 'C:\wamp\www\TMPress\wp-content\themes\twentytwelve\cpt.php' ) ..\functions.php:2 

Can you please let me know why this is happening? is there any better way to add a meta box containing a field and dropdown select box? I know there are some plugins out there for doing this but I really like to learn it on my own.

Answer 1

Try this

add_action( 'add_meta_boxes', 'cd_meta_box_add' ); function cd_meta_box_add() { add_meta_box( 'my-meta-box-id', 'My First Meta Box', 'cd_meta_box_cb', 'post', 'normal', 'high' ); } function cd_meta_box_cb() { echo 'What you put here, show\'s up in the meta box'; } 

ps: you have some extra problematic lines, at the top of your code, that I removed, namely:

add_meta_box( 'my-meta-box-id', 'My First Meta Box', 'cd_meta_box_cb', 'post', 'normal', 'high' ); 

Update:

To add the metabox to your custom post type edit page, replace 'post' with 'your-custom-post-type' in this line:

add_meta_box( 'my-meta-box-id', 'My First Meta Box', 'cd_meta_box_cb', 'your-custom-post-type', 'normal', 'high' );