How to upload a file to directory in yii2?

Create a read only attribute for your model like public $imageand proceed like

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

Follow the official documentation

https://github.com/yiisoft/yii2/blob/master/docs/guide/input-file-upload.md

Form Model

namespace app\models;

use yii\base\Model;
use yii\web\UploadedFile;

/**
* UploadForm is the model behind the upload form.
*/
class UploadForm extends Model
{
/**
 * @var UploadedFile|Null file attribute
 */
public $file;

/**
 * @return array the validation rules.
 */
public function rules()
{
    return [
        [['file'], 'file'],
    ];
}
}
?>

Form View

<?php
use yii\widgets\ActiveForm;

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

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

<button>Submit</button>

<?php ActiveForm::end(); ?>

Controller

Now create the controller that connects form and model together:

<?php
namespace app\controllers;

use Yii;
use yii\web\Controller;
use app\models\UploadForm;
use yii\web\UploadedFile;

class SiteController extends Controller
{
public function actionUpload()
{
    $model = new UploadForm();

    if (Yii::$app->request->isPost) {
        $model->file = UploadedFile::getInstance($model, 'file');

        if ($model->validate()) {                
            $model->file->saveAs('uploads/' . $model->file->baseName . '.' . $model->file->extension);
        }
    }

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

Instead of model->load(...) we are using UploadedFile::getInstance(...). [[\yii\web\UploadedFile|UploadedFile]] does not run the model validation. It only provides information about the uploaded file. Therefore, you need to run validation manually via $model->validate(). This triggers the [[yii\validators\FileValidator|FileValidator]] that expects a file:

 $file instanceof UploadedFile || $file->error == UPLOAD_ERR_NO_FILE //in code framework

If validation is successful, then we're saving the file:

 $model->file->saveAs('uploads/' . $model->file->baseName . '.' . $model->file->extension);

If you're using "basic" application template then folder uploads should be created under web.

That's it. Load the page and try uploading. Uplaods should end up in basic/web/uploads.

I really like Yii2 Dropzone.

Installation:

composer require --prefer-dist perminder-klair/yii2-dropzone "dev-master"

Usage:

<?php 
    echo \kato\DropZone::widget([
       'options' => [
           'url'=> Url::to(['resource-manager/upload']),
           'paramName'=>'image',
           'maxFilesize' => '10',
       ],
       'clientEvents' => [
           'complete' => "function(file){console.log(file)}",
           'removedfile' => "function(file){alert(file.name + ' is removed')}"
       ],
   ]);

   ?>

Controller:

public function actionUpload(){

        $model = new ResourceManager();
        $uploadPath = Yii::getAlias('@root') .'/uploads/';

        if (isset($_FILES['image'])) {
            $file = \yii\web\UploadedFile::getInstanceByName('image');
          $original_name = $file->baseName;  
          $newFileName = \Yii::$app->security
                            ->generateRandomString().'.'.$file->extension;
           // you can write save code here before uploading.
            if ($file->saveAs($uploadPath . '/' . $newFileName)) {
                $model->image = $newFileName;
                $model->original_name = $original_name;
                if($model->save(false)){
                    echo \yii\helpers\Json::encode($file);
                }
                else{
                    echo \yii\helpers\Json::encode($model->getErrors());
                }

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

        return false;
    }

in your view

use kartik\widgets\ActiveForm;
use kartik\widgets\FileInput;

$form = ActiveForm::begin(['options' => ['enctype'=>'multipart/form-data']]); //important
echo FileInput::widget([
                    'name' => 'filename',
                    'showUpload' => false,
                    'buttonOptions' => ['label' => false],
                    'removeOptions' => ['label' => false],
                    'groupOptions' => ['class' => 'input-group-lg']
                ]);
echo Html::submitButton('Submit', ['class'=>'btn btn-primary']);
ActiveForm::end();

in your controller

$file = \yii\web\UploadedFile::getInstanceByName('filename');
$file->saveAs('/your/directory/'.$file->name);