Creating custom field with drop down on new post page

Question

I Am trying to create a default custom field drop down with pre populated values from the DB to be shown while creating a new Post or editing a existing post.

I am aware about how to add a single custom field and have added few as follows

add_action('wp_insert_post', 'set_default_custom_fields'); 
function set_default_custom_fields($post_id) {
if ( $_GET['post_type'] != 'page' ) {
add_post_meta($post_id, 'email', 'xyz@mail.com', true);
}
}

This is working fine for me and i am able to see custom field with default value but i am not sure how to add a drop down in place of single text field, i tried something like this but seems like its not working.

 add_action('wp_insert_post', 'set_default_custom_fields'); 
  function set_default_custom_fields($post_id) {
    if ( $_GET['post_type'] != 'page' ) {
<select name="voodoo_dropdown" id="voodoo_dropdown">
        <option<?php selected( add_post_meta($post->ID, 'voodoo_dropdown', true), 'USA' ); ?>>USA</option>
        <option<?php selected( add_post_meta($post->ID, 'voodoo_dropdown', true), 'Canada' ); ?>>Canada</option>
        <option<?php selected( add_post_meta($post->ID, 'voodoo_dropdown', true), 'Mexico' ); ?>>Mexico</option>
        </select>
}
return ;
}

Due to my lack of knowledge i am not sure where i am doing wrong or what needs to be done to accomplish this task

Answer 1

Instead of defining the default values for custom fields, you should do like Milo says. You should have something like this in your functions.php. I tried to follow what you need, but didn't test it.

<?php

// action to add meta boxes
add_action( 'add_meta_boxes', 'voodoo_dropdown_metabox' );
// action on saving post
add_action( 'save_post', 'voodoo_dropdown_save' );

// function that creates the new metabox that will show on post
function voodoo_dropdown_metabox() {
    add_meta_box( 
        'voodoo_dropdown',  // unique id
        __( 'Voodoo Dropdown', 'mytheme_textdomain' ),  // metabox title
        'voodoo_dropdown_display',  // callback to show the dropdown
        'post'   // post type
    );
}

// voodoo dropdown display
function voodoo_dropdown_display( $post ) {

  // Use nonce for verification
  wp_nonce_field( basename( __FILE__ ), 'voodoo_dropdown_nonce' );

  // get current value
  $dropdown_value = get_post_meta( get_the_ID(), 'voodoo_dropdown', true );
  ?>
    <select name="voodoo_dropdown" id="voodoo_dropdown">
        <option value="USA" <?php if($dropdown_value == 'USA') echo 'selected'; ?>>USA</option>
        <option value="Canada" <?php if($dropdown_value == 'Canada') echo 'selected'; ?>>Canada</option>
        <option value="Mexico" <?php if($dropdown_value == 'Mexico') echo 'selected'; ?>>MEXICO</option>
    </select>
  <?php
}

// dropdown saving
function voodoo_dropdown_save( $post_id ) {

    // if doing autosave don't do nothing
  if ( defined( 'DOING_AUTOSAVE' ) && DOING_AUTOSAVE ) 
      return;

  // verify nonce
  if ( !wp_verify_nonce( $_POST['voodoo_dropdown_nonce'], basename( __FILE__ ) ) )
      return;


  // Check permissions
  if ( 'page' == $_POST['post_type'] ) 
  {
    if ( !current_user_can( 'edit_page', $post_id ) )
        return;
  }
  else
  {
    if ( !current_user_can( 'edit_post', $post_id ) )
        return;
  }

  // save the new value of the dropdown
  $new_value = $_POST['voodoo_dropdown'];
  update_post_meta( $post_id, 'voodoo_dropdown', $new_value );
}
?>

If you think this is too much complicated you can use a metaboxes plugin, find one in Wordpress Plugin directory that has already dropdowns.

Answer 2

Add your dropdown to the post edit screen in a meta box via add_meta_box, then on the save_post action you can check and save the selected option as post meta.

Answer 3

Once I had worked on a similar requirement, this is a raw code for that, hope this will help.

<?php
add_action( 'add_meta_boxes', 'yss_custom_post_cat_add' );
function yss_custom_post_cat_add() {
 add_meta_box( 'my-meta-box-id', 'My Custom Post Category', 'yss_custom_post_cat', 'post', 'normal', 'high' );
}

function yss_custom_post_cat( $post ) {
 $values = get_post_custom( $post->ID );
 $selected = isset( $values['custom_post_cat_select'] ) ? esc_attr( $values['custom_post_cat_select'][0] ) : '';
 wp_nonce_field( 'my_meta_box_nonce', 'meta_box_nonce' );
?>

   <p>
    <label for="custom_post_cat_select">Select your custom Post Category</label>
    <br>
    <select name="custom_post_cat_select" id="custom_post_cat_select">
     <option value="picture" <?php selected( $selected, 'none' ); ?>>(none)</option>
     <option value="picture" <?php selected( $selected, 'picture' ); ?>>Picture</option>
     <option value="video" <?php selected( $selected, 'video' ); ?>>Video</option>
     <option value="sports" <?php selected( $selected, 'sports' ); ?>>Sports</option>
     <option value="guesswho" <?php selected( $selected, 'guesswho' ); ?>>Guess Who</option>
     <option value="decisionpoll" <?php selected( $selected, 'decisionpoll' ); ?>>Decision Poll</option>
     <option value="audio" <?php selected( $selected, 'audio' ); ?>>Audio</option>
    </select>
   </p>
<?php
}

add_action( 'save_post', 'yss_custom_post_cat_save' );
function yss_custom_post_cat_save( $post_id ) {
 // Bail if we're doing an auto save
 if( defined( 'DOING_AUTOSAVE' ) && DOING_AUTOSAVE ) return;
 // if our nonce isn't there, or we can't verify it, bail
 if( !isset( $_POST['meta_box_nonce'] ) || !wp_verify_nonce( $_POST['meta_box_nonce'], 'my_meta_box_nonce' ) ) return;
 // if our current user can't edit this post, bail
 if( !current_user_can( 'edit_post' ) ) return;
 // now we can actually save the data
 $allowed = array(
            'a' => array( // on allow a tags
            'href' => array() // and those anchords can only have href attribute
    )
 );

// Probably a good idea to make sure your data is set
 if( isset( $_POST['custom_post_cat_select'] ) )
  update_post_meta( $post_id, 'custom_post_cat_select', esc_attr( $_POST['custom_post_cat_select'] ) );
}
?>