added doc example to gridview column classes

fixes #2276

framework/grid/ActionColumn.php

@@ -14,6 +14,18 @@ use yii\helpers\Html;
 /**
  * ActionColumn is a column for the [[GridView]] widget that displays buttons for viewing and manipulating the items.
  *
+ * To add an ActionColumn to the gridview, add it to the [[GridView::columns|columns]] configuration as follows:
+ *
+ * ```php
+ * 'columns' => [
+ *     // ...
+ *     [
+ *         'class' => 'yii\grid\ActionColumn',
+ *         // you may configure additional properties here
+ *     ],
+ * ]
+ * ```
+ *
  * @author Qiang Xue <qiang.xue@gmail.com>
  * @since 2.0
  */

framework/grid/CheckboxColumn.php

@@ -13,6 +13,19 @@ use yii\helpers\Html;
 
 /**
  * CheckboxColumn displays a column of checkboxes in a grid view.
+ *
+ *  * To add a CheckboxColumn to the [[GridView]], add it to the [[GridView::columns|columns]] configuration as follows:
+ *
+ * ```php
+ * 'columns' => [
+ *     // ...
+ *     [
+ *         'class' => 'yii\grid\CheckboxColumn',
+ *         // you may configure additional properties here
+ *     ],
+ * ]
+ * ```
+ *
  * Users may click on the checkboxes to select rows of the grid. The selected rows may be
  * obtained by calling the following JavaScript code:
  *

framework/grid/GridView.php

@@ -67,9 +67,9 @@ class GridView extends BaseListView
 	 * returns an array of the HTML attributes. The anonymous function will be called once for every
 	 * data model returned by [[dataProvider]]. It should have the following signature:
 	 *
-	 * ~~~php
+	 * ```php
 	 * function ($model, $key, $index, $grid)
-	 * ~~~
+	 * ```
 	 *
 	 * - `$model`: the current data model being rendered
 	 * - `$key`: the key value associated with the current data model
@@ -111,7 +111,7 @@ class GridView extends BaseListView
 	 * @var array grid column configuration. Each array element represents the configuration
 	 * for one particular grid column. For example,
 	 *
-	 * ~~~php
+	 * ```php
 	 * [
 	 *     ['class' => SerialColumn::className()],
 	 *     [
@@ -122,7 +122,7 @@ class GridView extends BaseListView
 	 *     ],
 	 *     ['class' => CheckboxColumn::className()],
 	 * ]
-	 * ~~~
+	 * ```
 	 *
 	 * If a column is of class [[DataColumn]], the "class" element can be omitted.
 	 *

framework/grid/SerialColumn.php

@@ -10,6 +10,18 @@ namespace yii\grid;
 /**
  * SerialColumn displays a column of row numbers (1-based).
  *
+ * To add a SerialColumn to the [[GridView]], add it to the [[GridView::columns|columns]] configuration as follows:
+ *
+ * ```php
+ * 'columns' => [
+ *     // ...
+ *     [
+ *         'class' => 'yii\grid\SerialColumn',
+ *         // you may configure additional properties here
+ *     ],
+ * ]
+ * ```
+ *
  * @author Qiang Xue <qiang.xue@gmail.com>
  * @since 2.0
  */