Recently I was developing plugin for image features. I have to add some fields to the attachment window of wordpress or I can say in Add media box.

We can achieve this by using two hooks of wordpress.
“attachment_fields_to_edit” and “attachment_fields_to_save”;

attachment_fields_to_edit

  • $form_fields is a special array which will be described in detail in a moment.
  • $post is the attachment as an object (attachments are treated as post objects in WordPress).

attachment_fields_to_save

  • $post is the attachment as an array (attachments are treated as post objects in WordPress).
  • $attachment is the attachment part of the form $_POST which will include the fields setup through the attachment_fields_to_edit hook.

Note: Be careful in your code, as $post is sent to one function as an object and to the other as an array.

We will add this fields information to Custom Fields.

How to add this Fields to Custom Fields for Working is Properly

The new fields being added will be saved as post meta, just like the custom fields section of the post/page edit screen. Fields prefixed with an underscore (_my_custom_field) will not be listed in the drop down of available custom fields on the post/page screen; all other existing post meta fields will be listed. We can use this knowledge to hide the fields we’re adding to the media form, since they aren’t relevant for posts/pages.

There is a similar rule to keep in mind when choosing the $form_fields array key to use for your new field. Here, if you use an underscore ($form_fields[‘_my_custom_field’]) your field will be skipped and will not be added to the form.

So in order to show our fields in the media form, but also not list them in the page/post custom fields drop down, we must combine both methods. This will invlove both the edit and save functions we’ll be creating. For the ‘attachment_fields_to_edit‘ hook we’ll set the $form_fields keys up to not have underscore prefixes, and for the ‘attachment_fields_to_save‘ hook we’ll prefix our fields with an underscore before saving them as post meta. This is a workaround worth doing in order to not muddy our users’ interface with unneeded info.

Hook 1: attachment_fields_to_edit

The $form_fields array has several options for including different types of inputs and custom content. I’ve compiled the various methods below with notes and screenshots of how they render in the form.

Text Input

Hook 2: attachment_fields_to_save

Saving your custom fields is a much simpler process than adding them to the form; just check if your field is set and update its value as post meta. Remeber to prefix your field with an underscore when saving to hide it on the post/page edit screen.

You can also add errors here that will automatically be displayed below your field in the form. The$post['errors'] array gets merged with the $form_fields array before being sent through theattachment_fields_to_edit hook.

Thanks to http://net.tutsplus.com

I have posted here for my future reference.