Difference between #3 and #4 of Special $variables in CGridView and CListView

The popular [CListView] and [CGridView] widgets each take a data provider and
iterate over each data object produced, calling the user's code to render each
row one at a time, and most are familiar with the use of the `$data` variable to
represent the current model object or array.

But there are additional special variables as well, including those that make
their way all the way back to the calling controller, and this page means to
reference them all.

CListView
---------
The [CListView] widget calls your partial rendering `_view` on each item,
setting these variables before calling each one:

* `$data` - the current object or hash being rendered
* `$index` - the zero-based index of the item being rendered (0, 1, 2, ...)
* `$this` - the owner of the widget, usually the calling controller
* `$widget` - the `CListView` widget itself

CGridView
---------
The [CGridView] widget displays data in tabular form, and when each `'value'
=> '...'` string is eval'd, these variables are available:

* `$data` - the current object or hash being rendered
* `$row` - the zero-based index of the item being rendered (0, 1, 2, ...)
* `$this` - the [CGridColumn] object representing the column being rendered
* `$this->grid` - the [CGridView] object that owns the column
* `$this->grid->owner` - the owner of the grid, usually the calling
controller

Passing your own variables
--------------------------
A very common request in the `#yii` channel is how to pass additional variables
to the widget that are available by the rendering code. Though this is
straightforward in `CListView`,Unfortunately, it's not so
simple as it looks, so unless the variable is readily available in the
controller (reachable by `$this` in `CListView` or
`$this->grid->owner` in `CGridView`.`CGridView`),
you pretty much have to extend the classes to do this.

InExtending `CListView` an additional `viewData`
parameter can be passed to the widget as an array with additional
variables:might look like:
~~~
[php]
$this->widget( 'zii.widgets.CListView', array(
    'dataProvider' => $dataProvider,
    'viewData' => array( 'switch' => true, 'blah' => 123 ),    // YOUR
OWN VARIABLES
    'itemView' => '_view',
) );
~~~
Then, in the `_view` you can refer to `$switch` or `$blah` directly right
alongside the other predefined variables.

For `CGridView` it appears that we have to extend the class to provide the
variables in the widget. This extended class might look like:
~~~
[php]
// components/SpecialGridView.php
Yii::import('zii.widgets.grid.CGridView');//
components/SpecialListView.php
Yii::import('zii.widgets.CListView');

class SpecialGridViewSpecialListView extends
CGridViewCListView {
    public $extraparam;
}
~~~
and then called in the controller as:
~~~
[php]
  // in your controller
 
$this->widget('SpecialGridView',$this->widget('SpecialListView',
array(
    'dataProvider' => $dataProvider,
    'itemView'     => '_view',      // partial rendering
    'extraparam'   => 1234          // your special parameter
    'columns' => array( ... ),
  ) );
~~~
This done, the extra parameter is available in each the
column`_view` as
`$this->grid->extraparam`.`$widget->extraparam`.

For `CGridView` it will be likewise, using `$this->grid->extraparam` from
within each column to get at the parameter.