protected function normalizeAttributes()
    {
        if ($this->attributes === null) {
            if ($this->model instanceof Model) {
                $this->attributes = $this->model->attributes();
            } elseif (is_object($this->model)) {
                $this->attributes = $this->model instanceof Arrayable ? $this->model->toArray() : array_keys(get_object_vars($this->model));
            } elseif (is_array($this->model)) {
                $this->attributes = array_keys($this->model);
            } else {
                throw new InvalidConfigException('The "model" property must be either an array or an object.');
            }
            sort($this->attributes);
        }

        foreach ($this->attributes as $i => $attribute) {
            if (is_string($attribute)) {
                if (!preg_match('/^([\w\.]+)(:(\w*))?(:(.*))?$/', $attribute, $matches)) {
                    throw new InvalidConfigException('The attribute must be specified in the format of "attribute", "attribute:format" or "attribute:format:label"');
                }
                $attribute = [
                    'attribute' => $matches[1],
                    'format' => isset($matches[3]) ? $matches[3] : 'text',
                    'label' => isset($matches[5]) ? $matches[5] : null,
                ];
            }

            if (!is_array($attribute)) {
                throw new InvalidConfigException('The attribute configuration must be an array.');
            }

            if (isset($attribute['visible']) && !$attribute['visible']) {
                unset($this->attributes[$i]);
                continue;
            }

            if (!isset($attribute['format'])) {
                $attribute['format'] = 'text';
            }
            if (isset($attribute['attribute'])) {
                $attributeName = $attribute['attribute'];
                if (!isset($attribute['label'])) {
                    $attribute['label'] = $this->model instanceof Model ? $this->model->getAttributeLabel($attributeName) : Inflector::camel2words($attributeName, true);
                }
                if (!array_key_exists('value', $attribute)) {
                    $attribute['value'] = ArrayHelper::getValue($this->model, $attributeName);
                }
            } elseif (!isset($attribute['label']) || !array_key_exists('value', $attribute)) {
                throw new InvalidConfigException('The attribute configuration requires the "attribute" element to determine the value and display label.');
            }

            $this->attributes[$i] = $attribute;
        }
    }