framework/base/View.php
public function init()
    {
        parent::init();
        if (is_array($this->theme)) {
            if (!isset($this->theme['class'])) {
                $this->theme['class'] = 'yii\base\Theme';
            }
            $this->theme = Yii::createObject($this->theme);
        } elseif (is_string($this->theme)) {
            $this->theme = Yii::createObject($this->theme);
        }
    }
public function init()
    {
        parent::init();
        if (is_array($this->theme)) {
            if (!isset($this->theme['class'])) {
                $this->theme['class'] = 'yii\base\Theme';
            }
            $this->theme = Yii::createObject($this->theme);
        } elseif (is_string($this->theme)) {
            $this->theme = Yii::createObject($this->theme);
        }
    }
Initializes the view component.