public function _register_one( $number = -1 ) {
		wp_register_sidebar_widget(
			$this->id,
			$this->name,
			$this->_get_display_callback(),
			$this->widget_options,
			array( 'number' => $number )
		);

		_register_widget_update_callback(
			$this->id_base,
			$this->_get_update_callback(),
			$this->control_options,
			array( 'number' => -1 )
		);

		_register_widget_form_callback(
			$this->id,
			$this->name,
			$this->_get_form_callback(),
			$this->control_options,
			array( 'number' => $number )
		);
	}

	/**
	 * Saves the settings for all instances of the widget class.
	 *
	 * @since 2.8.0
	 *
	 * @param array $settings Multi-dimensional array of widget instance settings.
	 */
	public function save_settings( $settings ) {
		$settings['_multiwidget'] = 1;
		update_option( $this->option_name, $settings );
	}

	/**
	 * Retrieves the settings for all instances of the widget class.
	 *
	 * @since 2.8.0
	 *
	 * @return array Multi-dimensional array of widget instance settings.
	 */
	public function get_settings() {

		$settings = get_option( $this->option_name );

		if ( false === $settings ) {
			$settings = array();
			if ( isset( $this->alt_option_name ) ) {
				// Get settings from alternative (legacy) option.
				$settings = get_option( $this->alt_option_name, array() );

				// Delete the alternative (legacy) option as the new option will be created using `$this->option_name`.
				delete_option( $this->alt_option_name );
			}
			// Save an option so it can be autoloaded next time.
			$this->save_settings( $settings );
		}

		if ( ! is_array( $settings ) && ! ( $settings instanceof ArrayObject || $settings instanceof ArrayIterator ) ) {
			$settings = array();
		}

		if ( ! empty( $settings ) && ! isset( $settings['_multiwidget'] ) ) {
			// Old format, convert if single widget.
			$settings = wp_convert_widget_settings( $this->id_base, $this->option_name, $settings );
		}

		unset( $settings['_multiwidget'], $settings['__i__'] );

		return $settings;
	}
}