DepDrop supports configuration of the bootstrap library version so that you can use this either with any Bootstrap version 3.x and above. For setting up the bootstrap version for your extension, you can configure the DepDrop::bsVersion property to one of the following.

• To use with bootstrap 3 library - you can set DepDrop::bsVersion property to any string starting with 3 (e.g. 3 or 3.3.7 or 3.x)

• To use with bootstrap 4 library - you can set DepDrop::bsVersion property to any string starting with 4 (e.g. 4 or 4.6.0 or 4.x)

• To use with bootstrap 5 library - you can set DepDrop::bsVersion property to any string starting with 5 (e.g. 5 or 5.1.0 or 5.x)

'params' => [
    'bsVersion' => '5.x', // this will set globally `bsVersion` to Bootstrap 5.x for all Krajee Extensions
    // other settings
    // 'adminEmail' => 'admin@example.com'
]

"yiisoft/yii2-bootstrap5": "@dev"

"yiisoft/yii2-bootstrap4": "@dev"

"yiisoft/yii2-bootstrap": "@dev"

The yii2-widget-depdrop extension can be installed automatically or manually using one of these options:

$ php composer.phar require kartik-v/yii2-widget-depdrop "dev-master"

"kartik-v/yii2-widget-depdrop": "dev-master"

• bsVersion: string | int, the bootstrap library version to be used for the extension. Refer the Bootstrap Info section for details and pre-requisites on setting this property.

  • To use with Bootstrap library - you can set this to any string starting with 3 (e.g. 3 or 3.3.7 or 4.x / 3.x)

  • To use with bootstrap 4 - you can set this to any string starting with 4 (e.g. 4 or 4.6.0 or 4.x)

  • To use with bootstrap 5 - you can set this to any string starting with 4 (e.g. 5 or 5.1.0 or 5.x)

• bsColCssPrefixes: array, the bootstrap grid column css prefixes mapping, the key is the bootstrap versions, and the value is an array containing the sizes and their corresponding grid column css prefixes. The class using this trait, must implement kartik\base\BootstrapInterface. If not set will default to:.

  [
     3 => [
        self::SIZE_X_SMALL => 'col-xs-',
        self::SIZE_SMALL => 'col-sm-',
        self::SIZE_MEDIUM => 'col-md-',
        self::SIZE_LARGE => 'col-lg-',
        self::SIZE_X_LARGE => 'col-lg-',
        self::SIZE_XX_LARGE => 'col-lg-',
     ],
     4 => [
        self::SIZE_X_SMALL => 'col-',
        self::SIZE_SMALL => 'col-sm-',
        self::SIZE_MEDIUM => 'col-md-',
        self::SIZE_LARGE => 'col-lg-',
        self::SIZE_X_LARGE => 'col-xl-',
        self::SIZE_XX_LARGE => 'col-xl-',
     ],
     5 => [
        self::SIZE_X_SMALL => 'col-',
        self::SIZE_SMALL => 'col-sm-',
        self::SIZE_MEDIUM => 'col-md-',
        self::SIZE_LARGE => 'col-lg-',
        self::SIZE_X_LARGE => 'col-xl-',
        self::SIZE_XX_LARGE => 'col-xxl-',
     ],
  ];
  

• type: int the type of dropdown list to be generated. Should be one of the following values:

  • 1 or DepDrop::TYPE_DEFAULT: render a default HTML select using \yii\helpers\Html::dropDownList.

  • 2 or DepDrop::TYPE_SELECT2: render advanced Select2 using \kartik\select2\Select2 widget.

  If not set the type will default to 1 or DepDrop::TYPE_DEFAULT.

• data: array the list of option data just like a standard Yii dropDownList, which can be generated using \yii\helpers\ArrayHelper::map(). However, a simple and efficient way to display a record for update, is that you set this to the last selected value and name as a single row array. This is because, the dropdown by default is disabled for select and this list will be overwritten by ajax operation based on dependent parent value. For example, if the last saved record for the dropdown field was id = 4, desc = 'Product 4', you can set the initial data for this field as:

  'data'=>[4=>'Product 4']
  

• select2Options: array the additional widget configuration options for the Select2. This is applicable only if type is set to DepDrop::TYPE_SELECT2.

• options: array the HTML attributes for the select element/ dropdown list.

• pluginOptions: array the options for the depdrop.js plugin. The following options can be configured:

  • url: string The url string for the controller action that will return the Json encoded dependent dropdown data via ajax.

  • depends: array The list of dependent parent dropdown element IDs (HTML ID attributes without any leading #).

  • loading: boolean whether to show a loading progress spin indicator in the dependent select when server is processing the ajax response. Defaults to true.

  • placeholder: string whether the dependent select has a default placeholder (with an empty value), when no records are found. You can set this to a label which will be displayed as an empty value. For optgroups this will be a disabled option. If you set this to null or empty string , it will not be displayed. Defaults to Select ....

  • placeholder: string the message to display when the ajax response returned from the server is null or an empty array. Defaults to No data found.

• pluginEvents: array the DepDrop JQuery events. You must define events in event-name=>event-function format. All events will be stacked in the sequence. Refer the plugin events documentation for details. For example:

  pluginEvents = [
      "depdrop:init"=>"function() { log('depdrop:init'); }",
      "depdrop:ready"=>"function() { log('depdrop:ready'); }",
      "depdrop:change"=>"function(event, id, value, count) { log(id); log(value); log(count); }",
      "depdrop:beforeChange"=>"function(event, id, value) { log('depdrop:beforeChange'); }",
      "depdrop:afterChange"=>"function(event, id, value) { log('depdrop:afterChange'); }",
      "depdrop:error"=>"function(event, id, value) { log('depdrop:error'); }",
  ];
  

/*
 * SCENARIO 1: A 3-level nested dependency example
 */
// THE VIEW
use kartik\depdrop\DepDrop;

$catList = [
    1 => 'Electronics',
    2 => 'Books',
    3 => 'Home & Kitchen'
];

// Parent 
echo $form->field($model, 'cat')->dropDownList($catList, ['id'=>'cat-id']);

// Child # 1
echo $form->field($model, 'subcat')->widget(DepDrop::classname(), [
    'options'=>['id'=>'subcat-id'],
    'pluginOptions'=>[
        'depends'=>['cat-id'],
        'placeholder'=>'Select...',
        'url'=>Url::to(['/site/subcat'])
    ]
]);

// Child # 2
echo $form->field($model, 'prod')->widget(DepDrop::classname(), [
    'pluginOptions'=>[
        'depends'=>['cat-id', 'subcat-id'],
        'placeholder'=>'Select...',
        'url'=>Url::to(['/site/prod'])
    ]
]);

// THE CONTROLLER
public function actionSubcat() {
    Yii::$app->response->format = \yii\web\Response::FORMAT_JSON;
    $out = [];
    if (isset($_POST['depdrop_parents'])) {
        $parents = $_POST['depdrop_parents'];
        if ($parents != null) {
            $cat_id = $parents[0];
            $out = self::getSubCatList($cat_id); 
            // the getSubCatList function will query the database based on the
            // cat_id and return an array like below:
            // [
            //    ['id'=>'<sub-cat-id-1>', 'name'=>'<sub-cat-name1>'],
            //    ['id'=>'<sub-cat_id_2>', 'name'=>'<sub-cat-name2>']
            // ]
            return ['output'=>$out, 'selected'=>''];
        }
    }
    return ['output'=>'', 'selected'=>''];
}

public function actionProd() {
    Yii::$app->response->format = \yii\web\Response::FORMAT_JSON;
    $out = [];
    if (isset($_POST['depdrop_parents'])) {
        $ids = $_POST['depdrop_parents'];
        $cat_id = empty($ids[0]) ? null : $ids[0];
        $subcat_id = empty($ids[1]) ? null : $ids[1];
        if ($cat_id != null) {
           $data = self::getProdList($cat_id, $subcat_id);
            /**
             * the getProdList function will query the database based on the
             * cat_id and sub_cat_id and return an array like below:
             *  [
             *      'out'=>[
             *          ['id'=>'<prod-id-1>', 'name'=>'<prod-name1>'],
             *          ['id'=>'<prod_id_2>', 'name'=>'<prod-name2>']
             *       ],
             *       'selected'=>'<prod-id-1>'
             *  ]
             */
           
           return ['output'=>$data['out'], 'selected'=>$data['selected']];
        }
    }
    return ['output'=>'', 'selected'=>''];
}

/*
 * SCENARIO 2: A 2-level dependency with optgroups with subcategory to be 
 * rendered by `\kartik\select2\Select2` widget.
 * In addition, it includes preselected data which you may have in a record 
 * update scenario (initial category is set to 'Category 1' and 
 * subcategory is set to 'Tablets'). Note: the `data` property must 
 * must be set for displaying the preselected value on initialization 
 * and must contain the key for the initial value.
 *
 * This example also considers an option where you pass additional `params`
 * to the ajax call by setting other form input identifiers.
 */
// THE VIEW
use kartik\depdrop\DepDrop;

// Parent 
echo $form->field($model, 'cat1')->dropDownList($majorCatList, ['id' => 'cat-id']);

// Additional input fields passed as params to the child dropdown's pluginOptions
echo Html::hiddenInput('input-type-1', 'Additional value 1', ['id' => 'input-type-1']);
echo Html::hiddenInput('input-type-2', 'Additional value 2', ['id' => 'input-type-2']);

// Child # 1
echo $form->field($model, 'subcat1')->widget(DepDrop::classname(), [
    'type' => DepDrop::TYPE_SELECT2,
    'data' => [2 => 'Tablets'],
    'options' => ['id' => 'subcat1-id', 'placeholder' => 'Select ...'],
    'select2Options' => ['pluginOptions' => ['allowClear' => true]],
    'pluginOptions' => [
        'depends' => ['cat1-id'],
        'url' => Url::to(['/site/subcat1']),
        'params' => ['input-type-1', 'input-type-2']
    ]
]);

// THE CONTROLLER
public function actionSubcat1() {
    Yii::$app->response->format = \yii\web\Response::FORMAT_JSON;
    $out = [];
    if (isset($_POST['depdrop_parents'])) {
        $parents = $_POST['depdrop_parents'];
        if ($parents != null) {
            $cat_id = $parents[0];
            $param1 = null;
            $param2 = null;
            if (!empty($_POST['depdrop_params'])) {
                $params = $_POST['depdrop_params'];
                $param1 = $params[0]; // get the value of input-type-1
                $param2 = $params[1]; // get the value of input-type-2
            }

            $out = self::getSubCatList1($cat_id, $param1, $param2); 
            // the getSubCatList1 function will query the database based on the
            // cat_id, param1, param2 and return an array like below:
            // [
            //    'group1' => [
            //        ['id' => '<sub-cat-id-1>', 'name' => '<sub-cat-name1>'],
            //        ['id' => '<sub-cat_id_2>', 'name' => '<sub-cat-name2>']
            //    ],
            //    'group2' => [
            //        ['id' => '<sub-cat-id-3>', 'name' => '<sub-cat-name3>'], 
            //        ['id' => '<sub-cat-id-4>', 'name' => '<sub-cat-name4>']
            //    ]            
            // ]
            
            
            $selected = self::getDefaultSubCat($cat_id);
            // the getDefaultSubCat function will query the database
            // and return the default sub cat for the cat_id
            
            return ['output' => $out, 'selected' => $selected];
        }
    }
    return ['output' => '', 'selected' => ''];
}

/*
 * SCENARIO 3: Four level dropdown dependency using `\kartik\select2\Select2` widget. Custom loading progress 
 * text is set for each dependent dropdown. In addition, it includes preselected values for dropdowns. 
 * 
 * NOTE: For a nested list scenario where the last child has the `initialize` plugin property set to 
 * `true` and depends on all 3 dropdowns before. This ensures each dependent list is loaded on initial page 
 * load in the right sequence and with the right preset values. Also you can see in this example, how after 
 * every change of a parent value, a preselected default value is possible to be set for each child.
 */
// THE VIEW
use kartik\depdrop\DepDrop;

// Top most parent
echo $form->field($account, 'lev0')->widget(Select2::classname(), [
    'data' => ArrayHelper::map(Account::find()->where('parent IS NULL')->asArray()->all(), 'id', 'name')
]);

// Child level 1
echo $form->field($account, 'lev1')->widget(DepDrop::classname(), [
    'data' => [6 => 'Bank'],
    'options' => ['placeholder' => 'Select ...'],
    'type' => DepDrop::TYPE_SELECT2,
    'select2Options' => ['pluginOptions' => ['allowClear' => true]],
    'pluginOptions' => [
        'depends' => ['account-lev0'],
        'url' => Url::to(['/account/child-account']),
        'loadingText' => 'Loading child level 1 ...',
    ]
]);

// Child level 2
echo $form->field($account, 'lev2')->widget(DepDrop::classname(), [
    'data' => [9 => 'Savings'],
    'options' => ['placeholder' => 'Select ...'],
    'type' => DepDrop::TYPE_SELECT2,
    'select2Options' => ['pluginOptions' => ['allowClear' => true]],
    'pluginOptions' => [
        'depends' => ['account-lev1'],
        'url' => Url::to(['/account/child-account']),
        'loadingText' => 'Loading child level 2 ...',
    ]
]);

// Child level 3
echo $form->field($account, 'lev3')->widget(DepDrop::classname(), [
    'data' => [12 => 'Savings A/C 2'],
    'options' => ['placeholder' => 'Select ...'],
    'type' => DepDrop::TYPE_SELECT2,
    'select2Options' => ['pluginOptions' => ['allowClear' => true]],
    'pluginOptions' => [
        'depends' => ['account-lev2'],
        'initialize' => true,
        'initDepends' => ['account-lev0'],
        'url' => Url::to(['/account/child-account']),
        'loadingText' => 'Loading child level 3 ...'
    ]
]);


// CONTROLLER
public function actionChildAccount() {
    Yii::$app->response->format = \yii\web\Response::FORMAT_JSON;
    $out = [];
    if (isset($_POST['depdrop_parents'])) {
        $id = end($_POST['depdrop_parents']);
        $list = Account::find()->andWhere(['parent' => $id])->asArray()->all();
        $selected  = null;
        if ($id != null && count($list) > 0) {
            $selected = '';
            foreach ($list as $i => $account) {
                $out[] = ['id' => $account['id'], 'name' => $account['name']];
                if ($i == 0) {
                    $selected = $account['id'];
                }
            }
            // Shows how you can preselect a value
            return ['output' => $out, 'selected' => $selected];
        }
    }
    return ['output' => '', 'selected' => ''];
}

The extension offers an easy method to generate dependent dropdown server actions as an alternative to server code in the examples before. The Dependent Dropdown action kartik\depdrop\DepDropAction can be used to generate the dependent option values via ajax response. A typical usage of this action in your controller could look like below (the example shows a subcategory action id to generate child dropdown values):

// inside the controller
public function actions()
{
    return \yii\helpers\ArrayHelper::merge(parent::actions(), [
        'subcategory' => [
            'class' => \kartik\depdrop\DepDropAction::className(),
            'outputCallback' => function ($selectedId, $params) {
                return [
                    [
                        'id' => 1,
                        'name' => 'Car',
                    ],
                    [
                        'id' => 2,
                        'name' => 'bike',
                    ],
                ];

                // if using with optgroup return something like below instead of above
                return [
                    'group1' => [
                        ['id' => '', 'name' => ''],
                        ['id' => '', 'name' => '']
                    ],
                    'group2' => [
                        ['id' => '', 'name' => ''],
                        ['id' => '', 'name' => '']
                    ]
                ];
            }
        ]
    ]);
}