Adding custom fields to woocommerce products

function.php

<?php

// From https://remicorson.com/mastering-woocommerce-products-custom-fields/

// Display Fields
add_action( 'woocommerce_product_options_general_product_data', 'woo_add_custom_general_fields' );

// Save Fields
add_action( 'woocommerce_process_product_meta', 'woo_add_custom_general_fields_save' );

function woo_add_custom_general_fields() {

    global $woocommerce, $post;
    
    echo '<div class="options_group">';
	  
    // Text Field
	woocommerce_wp_text_input( 
		array( 
			'id'          => '_text_field', 
			'label'       => __( 'My Text Field', 'woocommerce' ), 
			'placeholder' => 'http://',
			'desc_tip'    => 'true',
			'description' => __( 'Enter the custom value here.', 'woocommerce' ) 
		)
	);

	// Number Field
	woocommerce_wp_text_input( 
		array( 
			'id'                => '_number_field', 
			'label'             => __( 'My Number Field', 'woocommerce' ), 
			'placeholder'       => '', 
			'description'       => __( 'Enter the custom value here.', 'woocommerce' ),
			'type'              => 'number', 
			'custom_attributes' => array(
					'step' 	=> 'any',
					'min'	=> '0'
				) 
		)
	);

	// Textarea
	woocommerce_wp_textarea_input( 
		array( 
			'id'          => '_textarea', 
			'label'       => __( 'My Textarea', 'woocommerce' ), 
			'placeholder' => '', 
			'description' => __( 'Enter the custom value here.', 'woocommerce' ) 
		)
	);

	// Select
	woocommerce_wp_select( 
	array( 
		'id'      => '_select', 
		'label'   => __( 'My Select Field', 'woocommerce' ), 
		'options' => array(
			'one'   => __( 'Option 1', 'woocommerce' ),
			'two'   => __( 'Option 2', 'woocommerce' ),
			'three' => __( 'Option 3', 'woocommerce' )
			)
		)
	);

	// Checkbox
	woocommerce_wp_checkbox( 
	array( 
		'id'            => '_checkbox', 
		'wrapper_class' => 'show_if_simple', 
		'label'         => __('My Checkbox Field', 'woocommerce' ), 
		'description'   => __( 'Check me!', 'woocommerce' ) 
		)
	);

	// Hidden field
	woocommerce_wp_hidden_input(
	array( 
		'id'    => '_hidden_field', 
		'value' => 'hidden_value'
		)
	);

	// Product Select
	?>
	<p class="form-field product_field_type">
	<label for="product_field_type"><?php _e( 'Product Select', 'woocommerce' ); ?></label>
	<select id="product_field_type" name="product_field_type[]" class="ajax_chosen_select_products" multiple="multiple" data-placeholder="<?php _e( 'Search for a product&hellip;', 'woocommerce' ); ?>">
		<?php
			$product_field_type_ids = get_post_meta( $post->ID, '_product_field_type_ids', true );
			$product_ids = ! empty( $product_field_type_ids ) ? array_map( 'absint',  $product_field_type_ids ) : null;
			if ( $product_ids ) {
				foreach ( $product_ids as $product_id ) {
					$product      = get_product( $product_id );
					$product_name = woocommerce_get_formatted_product_name( $product );
					echo '<option value="' . esc_attr( $product_id ) . '" selected="selected">' . esc_html( $product_name ) . '</option>';
				}
			}
		?>
	</select> <img class="help_tip" data-tip='<?php _e( 'Your description here', 'woocommerce' ) ?>' src="<?php echo $woocommerce->plugin_url(); ?>/assets/images/help.png" height="16" width="16" />
	</p>
	<?php

	// Custom field Type
	?>
	<p class="form-field custom_field_type">
		<label for="custom_field_type"><?php echo __( 'Custom Field Type', 'woocommerce' ); ?></label>
		<span class="wrap">
			<?php $custom_field_type = get_post_meta( $post->ID, '_custom_field_type', true ); ?>	
			<input placeholder="<?php _e( 'Field One', 'woocommerce' ); ?>" class="" type="number" name="_field_one" value="<?php echo $custom_field_type[0]; ?>" step="any" min="0" style="width: 80px;" />
			<input placeholder="<?php _e( 'Field Two', 'woocommerce' ); ?>" type="number" name="_field_two" value="<?php echo $custom_field_type[1]; ?>" step="any" min="0" style="width: 80px;" />
		</span>
		<span class="description"><?php _e( 'Place your own description here!', 'woocommerce' ); ?></span>
	</p>
	<?php
  
  echo '</div>';
	
}

function woo_add_custom_general_fields_save( $post_id ){
	
	// Text Field
	$woocommerce_text_field = $_POST['_text_field'];
	if( !empty( $woocommerce_text_field ) )
		update_post_meta( $post_id, '_text_field', esc_attr( $woocommerce_text_field ) );
		
	// Number Field
	$woocommerce_number_field = $_POST['_number_field'];
	if( !empty( $woocommerce_number_field ) )
		update_post_meta( $post_id, '_number_field', esc_attr( $woocommerce_number_field ) );
		
	// Textarea
	$woocommerce_textarea = $_POST['_textarea'];
	if( !empty( $woocommerce_textarea ) )
		update_post_meta( $post_id, '_textarea', esc_html( $woocommerce_textarea ) );
		
	// Select
	$woocommerce_select = $_POST['_select'];
	if( !empty( $woocommerce_select ) )
		update_post_meta( $post_id, '_select', esc_attr( $woocommerce_select ) );
		
	// Checkbox
	$woocommerce_checkbox = isset( $_POST['_checkbox'] ) ? 'yes' : 'no';
	update_post_meta( $post_id, '_checkbox', $woocommerce_checkbox );
	
	// Custom Field
	$custom_field_type =  array( esc_attr( $_POST['_field_one'] ), esc_attr( $_POST['_field_two'] ) );
	update_post_meta( $post_id, '_custom_field_type', $custom_field_type );
	
	// Hidden Field
	$woocommerce_hidden_field = $_POST['_hidden_field'];
	if( !empty( $woocommerce_hidden_field ) )
		update_post_meta( $post_id, '_hidden_field', esc_attr( $woocommerce_hidden_field ) );
		
	// Product Field Type
	$product_field_type =  $_POST['product_field_type'];
	update_post_meta( $post_id, '_product_field_type_ids', $product_field_type );
	
}


add_action( 'woocommerce_product_write_panel_tabs', 'woo_add_custom_admin_product_tab' );

function woo_add_custom_admin_product_tab() {
	?>
	<li class="custom_tab"><a href="#custom_tab_data"><?php _e('My Custom Tab', 'woocommerce'); ?></a></li>
	<?php
}