add term metabox to custom taxonomy - using WP 4.4 term meta functions

add-term-to-custom-taxonomy.php

<?php

// source: http://wordpress.stackexchange.com/questions/211703/need-a-simple-but-complete-example-of-adding-metabox-to-taxonomy
// code authored by jgraup - http://wordpress.stackexchange.com/users/84219/jgraup


// CREATE CUSTOM TAXONOMY

add_action( 'init', '___create_my_custom_tax' );

function ___create_my_custom_tax() {
	register_taxonomy(
		'my-tax',
		'post',
		array(
			'label' => __( 'Custom Taxonomy' ),
			'rewrite' => array( 'slug' => 'custom-tax' ),
			'hierarchical' => true,
		)
	);
}

// REGISTER TERM META

add_action( 'init', '___register_term_meta_text' );

function ___register_term_meta_text() {

    register_meta( 'term', '__term_meta_text', '___sanitize_term_meta_text' );
}

// SANITIZE DATA

function ___sanitize_term_meta_text ( $value ) {
    return sanitize_text_field ($value);
}

// GETTER (will be sanitized)

function ___get_term_meta_text( $term_id ) {
  $value = get_term_meta( $term_id, '__term_meta_text', true );
  $value = ___sanitize_term_meta_text( $value );
  return $value;
}

// ADD FIELD TO CATEGORY TERM PAGE

add_action( 'my-tax_add_form_fields', '___add_form_field_term_meta_text' );

function ___add_form_field_term_meta_text() { ?>
    <?php wp_nonce_field( basename( __FILE__ ), 'term_meta_text_nonce' ); ?>
    <div class="form-field term-meta-text-wrap">
        <label for="term-meta-text"><?php _e( 'TERM META TEXT', 'text_domain' ); ?></label>
        <input type="text" name="term_meta_text" id="term-meta-text" value="" class="term-meta-text-field" />
    </div>
<?php }


// ADD FIELD TO CATEGORY EDIT PAGE

add_action( 'my-tax_edit_form_fields', '___edit_form_field_term_meta_text' );

function ___edit_form_field_term_meta_text( $term ) {

    $value  = ___get_term_meta_text( $term->term_id );

    if ( ! $value )
        $value = ""; ?>

    <tr class="form-field term-meta-text-wrap">
        <th scope="row"><label for="term-meta-text"><?php _e( 'TERM META TEXT', 'text_domain' ); ?></label></th>
        <td>
            <?php wp_nonce_field( basename( __FILE__ ), 'term_meta_text_nonce' ); ?>
            <input type="text" name="term_meta_text" id="term-meta-text" value="<?php echo esc_attr( $value ); ?>" class="term-meta-text-field"  />
        </td>
    </tr>
<?php }


// SAVE TERM META (on term edit & create)

add_action( 'edit_my-tax',   '___save_term_meta_text' );
add_action( 'create_my-tax', '___save_term_meta_text' );

function ___save_term_meta_text( $term_id ) {

    // verify the nonce --- remove if you don't care
    if ( ! isset( $_POST['term_meta_text_nonce'] ) || ! wp_verify_nonce( $_POST['term_meta_text_nonce'], basename( __FILE__ ) ) )
        return;

    $old_value  = ___get_term_meta_text( $term_id );
    $new_value = isset( $_POST['term_meta_text'] ) ? ___sanitize_term_meta_text ( $_POST['term_meta_text'] ) : '';


    if ( $old_value && '' === $new_value )
        delete_term_meta( $term_id, '__term_meta_text' );

    else if ( $old_value !== $new_value )
        update_term_meta( $term_id, '__term_meta_text', $new_value );
}

// MODIFY COLUMNS (add our meta to the list)

add_filter( 'manage_edit-my-tax_columns', '___edit_term_columns', 10, 3 );

function ___edit_term_columns( $columns ) {

    $columns['__term_meta_text'] = __( 'TERM META TEXT', 'text_domain' );

    return $columns;
}

// RENDER COLUMNS (render the meta data on a column)

add_filter( 'manage_my-tax_custom_column', '___manage_term_custom_column', 10, 3 );

function ___manage_term_custom_column( $out, $column, $term_id ) {

    if ( '__term_meta_text' === $column ) {

        $value  = ___get_term_meta_text( $term_id );

        if ( ! $value )
            $value = '';

        $out = sprintf( '<span class="term-meta-text-block" style="" >%s</div>', esc_attr( $value ) );
    }

    return $out;
}

Make admin columns sortable

Using edit_term and create_term seems better way.

https://developer.wordpress.org/reference/hooks/edit_term/
https://developer.wordpress.org/reference/hooks/create_term/