未定义的偏移量：0表示for循环

I'm newbie in laravel. My code aim to get all selected files and save to public->upload folder. this is my code

public function store(Request $request)
{
    /**
    * @var UploadedFile
    */

    $files = $request->all();
    for ($i=0; $i < count($files); $i++) { 
           $file = $files[$i]->file('file');
           $file->store('upload', 'public');

    }

}

I have error "Undefined offset: 0". Thanks for the help.

Use foreach loop like this

  $files = $request->all();
    foreach ($files as $items) { 
           $file = $items->file('file');
           $file->store('upload', 'public');
    }

Use isset() to check whether its exist or not then upload.

$files = $request->all();
for ($i=0; $i < count($files); $i++) { 
     if(isset($files[$i])) {
       $file = $files[$i]->file('file');
       $file->store('upload', 'public');
    }
}