yii\grid\GridView::initColumns PHP Method

    protected function initColumns()
    {
        if (empty($this->columns)) {
            $this->guessColumns();
        }
        foreach ($this->columns as $i => $column) {
            if (is_string($column)) {
                $column = $this->createDataColumn($column);
            } else {
                $column = Yii::createObject(array_merge(['class' => $this->dataColumnClass ?: DataColumn::className(), 'grid' => $this], $column));
            }
            if (!$column->visible) {
                unset($this->columns[$i]);
                continue;
            }
            $this->columns[$i] = $column;
        }
    }

 /**
  * @inheritdoc
  */
 protected function initColumns()
 {
     foreach ($this->_template as $column) {
         if ($column != 'action') {
             $this->setupDataColumn($column);
         }
         if ($column == 'action') {
             $this->setupActionColumn();
         }
     }
     parent::initColumns();
 }