下拉框 带提示

 <?=$form->field(
                        $model,
                        'unit_id',
                        [
                            'inputOptions' => [
                                'class' => 'required',
                            ],
                            'template' => '{input}',
                        ]
                    )->dropDownList($list_unit,['prompt'=>'请选择计数单位'])?>

来自为知笔记(Wiz)