framework/behaviors/AttributesBehavior.php
protected function getValue($attribute, $event)
    {
        if (!isset($this->attributes[$attribute][$event->name])) {
            return null;
        }
        $value = $this->attributes[$attribute][$event->name];
        if ($value instanceof Closure || (is_array($value) && is_callable($value))) {
            return $value($event, $attribute);
        }

        return $value;
    }
protected function getValue($attribute, $event)
    {
        if (!isset($this->attributes[$attribute][$event->name])) {
            return null;
        }
        $value = $this->attributes[$attribute][$event->name];
        if ($value instanceof Closure || (is_array($value) && is_callable($value))) {
            return $value($event, $attribute);
        }

        return $value;
    }
Returns the value for the current attributes.
This method is called by [[evaluateAttributes()]]. Its return value will be assigned
to the target attribute corresponding to the triggering event.
@param string $attribute target attribute name
@param Event $event the event that triggers the current attribute updating.
@return mixed the attribute value