dependent dropdown

//controller
public function actionCreate()
    {
        $model = new Transaksi();

        if ($model->load(Yii::$app->request->post()) && $model->save()) {
            return $this->redirect(['view', 'id' => $model->id_transaksi]);
        } else {
            return $this->render('create', [
                'model' => $model,
            ]);
        }
    }

    //depdrop
    public function actionDepdrop(){
        $model = new Transaksi();

        return $this->render('depdrop', [
            'model' => $model,
        ]);
    }
    public function actionSub($id)
    {
        $regencies = \app\models\SubBidang::find()
                ->where(['id_bidang' => $id])
                ->orderBy('id_sub_bidang ASC')
                ->all();

        if ($regencies) {
            echo "<option> - Pilih Subbb Bidang -</option>";
            foreach($regencies as $regency) {
                echo "<option value='".$regency->id_sub_bidang."'>".$regency->id_sub_bidang . " " . $regency->nama_sub_bidang."</option>";
            }
        } else
            echo "<option>-</option>";

    }
    public function actionLayanan($id)
    {
        $districts = \app\models\Layanan::find()
                ->where(['id_sub_bidang' => $id])
                ->orderBy('id_layanan ASC')
                ->all();

        if ($districts) {
            echo "<option> - Pilih Layanan -</option>";
            foreach($districts as $district) {
                echo "<option value='".$district->id_layanan."'>".$district->id_layanan." ".$district->nama_layanan."</option>";
            }
        } else
            echo "<option>-</option>";

    }
    public function actionSyarat($id)
    {
        $villages = \app\models\Syarat::find()
                ->where(['id_layanan' => $id])
                ->orderBy('id_syarat ASC')
                ->all();

        if ($villages) {
            echo "<option> - Pilih Syarat -</option>";
            foreach($villages as $village) {
                echo "<option value='".$village->id_syarat."'>".$village->id_syarat." ".$village->nama_syarat."</option>";
            }
        } else
            echo "<option>-</option>";

    }
    //depdrop
//controller

//_form
<?php

use yii\helpers\Html;
use yii\widgets\ActiveForm;

use yii\helpers\ArrayHelper;

use common\models\Pegawai;
use common\models\Bidang;
use common\models\SubBidang;
use common\models\Layanan;
use dosamigos\ckeditor\CKEditor;

/* @var $this yii\web\View */
/* @var $model common\models\Transaksi */
/* @var $form yii\widgets\ActiveForm */
?>



<div class="Transaksi-form">

    <div class="col-md-12" style="text-align:left">
        <!-- Form horizontal layout striped -->
        <?php $form = ActiveForm::begin(['options' => ['enctype' => 'multipart/form-data','class'=>'form-horizontal panel panel-default']]) ?>

            <div class="panel-heading">
                <h3 class="panel-title">Transaksi </h3>
            </div>
            <div class="panel-body">

                <div class="form-group">
                    <label class="col-sm-2 control-label">Nama Pegawai</label>
                    <div class="col-sm-6">
                        <?=
                            $form->field($model, 'id_pegawai')->dropDownList(
                                ArrayHelper::map(Pegawai::find()->orderBy(['nama_pegawai'=> SORT_ASC])->all(),'id_pegawai','nama_pegawai'),
                                ['prompt'=>'Pilih Pegawai', 'class'=>'form-control']
                            )->label(false)
                        ?>
                    </div>
                </div>
                <?php $provinces = ArrayHelper::map(Bidang::find()->asArray()->all(), 'id_bidang', 'nama_bidang');?>

                <div class="form-group">
                    <label class="col-sm-2 control-label">Bidang</label>
                    <div class="col-sm-6">
                        <?php
                            // $form->field($model, 'id_bidang')->dropDownList(
                                // ArrayHelper::map(Bidang::find()->orderBy(['nama_bidang'=> SORT_ASC])->all(),'id_bidang','nama_bidang'),
                                // ['prompt'=>'Pilih Bidang', 'class'=>'form-control']
                            // )->label(false)

                            echo Html::dropDownList('id_bidang', null, $provinces, [
                            'prompt' => '-Pilih Bidang-',
                            'onchange' => '$.post("'.Yii::$app->urlManager->createUrl('transaksi/sub').'&id="+$(this).val(), function(data){$("select#sub").html(data);});',
                            'class' => 'form-control'
                            ]);
                        ?>
                    </div>
                </div>

                <div class="form-group">
                    <label class="col-sm-2 control-label">Sub Bidang</label>
                    <div class="col-sm-6">
                        <?php
                            // $form->field($model, 'id_sub_bidang')->dropDownList(
                                // ArrayHelper::map(SubBidang::find()->orderBy(['nama_sub_bidang'=> SORT_ASC])->all(),'id_sub_bidang','nama_sub_bidang'),
                                // ['prompt'=>'Pilih Sub Bidang', 'class'=>'form-control']
                            // )->label(false)
                            echo Html::dropDownList('id_sub_bidang', null, [], [
                                'prompt' => 'Pilih Sub Bidang',
                                'id' => 'sub',
                                'onchange' => '$.post("'.Yii::$app->urlManager->createUrl('transaksi/layanan').'&id="+$(this).val(), function(data){$("select#layanan").html(data);});',
                                'class' => 'form-control'
                            ]);
                        ?>
                    </div>
                </div>


                <div class="form-group">
                    <label class="col-sm-2 control-label">Layanan</label>
                    <div class="col-sm-6">
                        <?php
                            // $form->field($model, 'id_layanan')->dropDownList(
                                // ArrayHelper::map(Layanan::find()->orderBy(['nama_layanan'=> SORT_ASC])->all(),'id_layanan','nama_layanan'),
                                // ['prompt'=>'Pilih Layanan', 'class'=>'form-control']
                            // )->label(false)

                            echo Html::dropDownList('id_layanan', null, [], [
                                'prompt' => 'Pilih Layanan',
                                'id' => 'layanan',
                                'class' => 'form-control'
                            ]);
                        ?>
                    </div>
                </div>

            </div>
            <div class="panel-footer">
                <?= Html::submitButton($model->isNewRecord ? 'Create' : 'Update', ['class' => $model->isNewRecord ? 'btn btn-success' : 'btn btn-primary']) ?>
                <button type="reset" class="btn btn-inverse">Reset</button>
            </div>
        <?php ActiveForm::end(); ?>
        <!--/ Form horizontal layout striped -->
    </div>
</div>




//_form