In web development, file uploading and downloading is a very common requirement. In the Yii framework, we can easily implement file operations through the built-in file upload and download functions. In this article, we will introduce how to upload and download files in Yii framework.

1. Upload files

File upload usually involves two processes: rendering of the upload form and processing of file upload. In the Yii framework, we can render the upload form by using Active Form, and then use UploadedFile in the backend controller to handle the file upload process.

1. Rendering the upload form

To upload files, you first need to render the upload form. In the Yii framework, we can use Active Form to quickly generate upload forms. Here is an example of a simple file upload form:

$form = ActiveForm::begin([

'options' => ['enctype' => 'multipart/form-data']

]) ?>

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

Upload

In the code, we use Active Form's begin() and end() methods to wrap the form, and set the 'enctype' attribute to 'multipart/form-data' to support File Upload. Then, we use the $form->field() method to generate the form field. The name of the field is an attribute in our model, here we use 'file'. Finally, we add a submit button that users can click to upload files.

2. Handling file upload

Once the user clicks the upload button, we need to handle the file upload in the backend controller. In Yii framework, we can use UploadedFile class to handle file upload. The following is a simple file upload controller code:

public function actionUpload()
{

$model = new FileModel();

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

    if($model->upload()){
        Yii::$app->session->setFlash('success', '文件上傳成功');
    }else{
        Yii::$app->session->setFlash('error', '文件上傳失敗');
    }
}

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

}

In the code, we first instantiate a FileModel class and then checks whether the current request is a POST request. If it is a POST request, we use the UploadedFile::getInstance() method to get the uploaded file. 'file' is the name of the upload form field and the attribute name we defined in the model. We then use the $model->upload() method to handle the file upload operation. If the file upload is successful, we will set a success message, otherwise an error message. Finally, we return a view file and pass the $model variable as parameter, which will contain the information of the uploaded results.

3. Handling file upload operations

The last step to implement file upload is to implement the $model->upload() method. The following is a simple implementation of the $model->upload() method:

public function upload()
{

if ($this->validate()) {
    $file_path = 'uploads/' . $this->file->baseName . '.' . $this->file->extension;

    if ($this->file->saveAs($file_path)) {
        return true;
    } else {
        return false;
    }
} else {
    return false;
}

}

In the code, We first check if the uploaded file has been verified. We then create a file path for the uploaded file (combining the filename and extension and storing it in the upload folder). Finally, we use the $this->file->saveAs() method to save the file to disk. We will return true if the save is successful, false otherwise.

2. Download the file

To download the file, we need to provide a download link, and the user can click the link to download the file. In the Yii framework, we can implement file downloading by using the Response object. The following is a simple file download controller code:

public function actionDownload()
{

$file_path = 'uploads/test.txt';

if(file_exists($file_path)){
    return Yii::$app->response->sendFile($file_path);
}else{
    throw new yiiwebNotFoundHttpException('文件不存在');
}

}

In the code, we first get the download file path. Then we check if the file exists. If the file exists, we use the Yii::$app->response->sendFile() method to send the file to the user. If the file does not exist, we will throw an exception.

3. Display file links in the view

Finally, we need to display file upload and download links in the view. Here is a simple view file example:

File Upload and Download Example

File Upload

render('_upload_form', ['model' => $model]) ?>

File Download

Download file:

In the code, we first render the file by including the _upload_form view file Upload form. Then, we use the Url::to() method to generate a file download link and add it to the page.

Summary

In this article, we introduced how to create a file in Yii File upload and download are implemented in the framework. To upload a file, you need to render the upload form and process the file upload. To download a file, you need to provide a download link and use the Response object to implement the file download. When implementing the file upload and download functions, we need to consider security and directory Access permissions and other issues. In actual applications, we need to handle these issues carefully to ensure the security and stability of file uploading and downloading.

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