Xurshidbek

$img = imagine\Image::getImagine()->open(Yii::getAlias($fullName));

$size = $img->getSize();
$ratio = $size->getWidth()/$size->getHeight();

$width = 200;
$height = round($width/$ratio);

$box = new Box($width, $height);
$img->resize($box)->save($filePath.'/thumb/' . $fileName);

// OR:

imagine\Image::thumbnail($fullName,$width,$height)
        ->save($filePath.'/thumb/' . $fileName);

\yii\helpers\StringHelper::truncate('Текст который нужно обрезать',150,'...');

<?= ListView::widget([
        'dataProvider' => $dataProvider,
        'itemOptions' => ['tag' => false],
     //'itemView' => '_teaser',
        'itemView' => function ($model, $key, $index, $widget) {
            return $this->render('_teaser', [
                'model' => $model,
                'key' => $key,
                'index' => $index,
                'widget' => $widget,
            ]);
        }
    ]) ?>

<div class="item" data-key="<?=$model->id?>">
...
</div>

<?php if (($index+1) % 3 == 0) : ?>
я после третьего?
<?php endif; ?>