Fileinput issue in ActiveForm when updating via Yii 2 - file-upload

Question

I am using Yii2 framwork. My file upload function worked well when I upload a single img, while when I click the posed article and I only want to update the post again(Suppose I didn't want to update the img, I only want to update other contents). But I found my uploaded file were replaced with an empty value(varchar type) when I click view. my uploaded img can't show out.
I do tried to fixed by myself as below, But the existing file value can't be saved when I click the submit button.
<?php
if (($post->file) != "") {
echo $form->field($post, 'file')->textInput()->hint('My currently uploaded file')->label('My Photo') ;
}
else{
echo $form->field($post, 'file')->fileInput()->hint('To upload a new file')->label('My Photo') ;
}
?>
When I click submit button, my existing file was gone.
Is there any good way to fix it.
Thanks for your opinions in advance.

Answer 1

Use another variable in your model for upload a file.
For example use file_field name for get file from submitted and store in file field.
class PostModel extends Model
{
/**
*
* #var UploadedFile
*/
public $file_field;
public function rules() {
return [
['file_field', 'file'],
];
}
}
echo $form->field($post, 'file_field')->fileInput()->hint('To upload a new file')->label('My Photo') ;
$post->file_field = UploadedFile::getInstance($post, 'file_field');
For upload new file check the file_field:
if ($post->file_field) {
// $post->file old file
// Save $post->file_field and store name in $post->file
}

Answer 2

Add a rule to your model rules:
[['file'], 'file', 'skipOnEmpty' => true, 'extensions' => 'png, jpg'],
and check for an empty upload in your controller:
if (Yii::$app->request->isPost) {
$ok = true;
// process your other fields...
...
// process image file only if there is one
$post->file= UploadedFile::getInstance($post, 'file');
if ($post->file && $post->upload()) {
}
if ($ok) {
return $this->redirect(...);
}
}
See Yii2 docs and the Yii2 guide for detailed infos about file upload.