yii2 文件无法上传 [ 2.0 版本 ]

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

<?= $form->field($model, 'file')->fileInput() ?>

<button>Submit</button>

<?php ActiveForm::end() ?>

models：

public function rules()
{
    return [
        [['file'], 'file', 'skipOnEmpty' => false,'extensions'=>'xls,xlsx'],
    ];
}

public function upload()
{
    if($this->validate()){
        $this->file->saveAs('uploads/' . $this->file->baseName . '.' . $this->file->extension);
        return true;

    }else{
        return false;
    }
}

控制器

    $model = new UploadForm();
    if(Yii::$app->request->post()){
        $model->file = UploadedFile::getInstance($model, 'file');
        if($model->upload()){
            //文件上传成功
            echo "File successfully uploaded";
            return;
        }
    }

    return $this->render('upload', ['model' => $model]);

发现压根就没有上传的文件，文件名搜不到，是不是没有在activeform引入方法URL