@sevin 谢谢，借你吉言！

在models层随便建个模型，

控制器层调用：

<?php
public function actionDatepicker(){
    $model=new 模型;
    return $this->render('datepicker',['model'=>$model]);
}
?>

在视图层：

<?php
use dosamigos\datepicker\DatePicker;
use dosamigos\datepicker\DateRangePicker;
use yii\widgets\ActiveForm;
    
echo DatePicker::widget([
    'model' => $model,
    'language'=>'zh_cn',
    'attribute' => 'time',
    'template' => '{addon}{input}',
    'clientOptions' => [
        'autoclose' => true,
        //'format' => 'dd-M-yyyy'
        'format'=>'yyyy-mm-dd',
    ]
    
]);
?>

session 存放在服务端，cookie 存在客户端。
一般来说：
session用来存储短期信息，php默认session存储的时间约24分钟。
cookie用来存储长期信息，经常用到的是存储 用户登录信息，下次访问网站就不用再登录。

东西是死的，要活用。

model层：

<?php
    namespace app\models;
    use Yii;
    use yii\base\model;
    use yii\db\ActiveRecord;
    use yii\web\UploadedFile;
    
    class Upload extends Model {
        public $file;
        public function rules(){
            return [
                [['file'],'file','extensions' => 'jpg, png,jpeg', 'mimeTypes' => 'image/jpeg, image/png, image/jpeg','skipOnEmpty' => false],
            ];
        }
    }
?>

控制器层：

public function actionLoad(){
    $upload=new Upload;
    $request=Yii::$app->request;
    if($request->isPost){
        //echo 'a';die;
        $upload->file=UploadedFile::getInstance($upload,'file');
        //print_r($upload);die;
        if($upload->file && $upload->validate()){
            $upload->file->saveAs('uploads/' . $upload->file->baseName . '.' . $upload->file->extension);
        }else{
            echo '<script>alert("格式不正确")</script>';
            die;
        }
    }
    return $this->render('upfile',['model'=>$upload]);
}

视图层：

<?php
    use yii\helpers\Html;
    use yii\bootstrap\ActiveForm;
?>

<?php $form = ActiveForm::begin(['options' => ['enctype' => 'multipart/form-data']]) ?>

<?= $form->field($model, 'file')->fileInput()->label('选择文件') ?>

<button>Submit</button>

<?php ActiveForm::end() ?>