Codeigniter 3/ form_multiselect / Cannot understand how to do validation - codeigniter

Question

I have the following in my view among other fields:
echo form_multiselect('person_tags[]', $options, set_value('person_tags[]'), $atribute_tag);
The above produces a list of tags, as expected. More than one choice can be made from the list, as expected.
When the form is submitted, validation is run as follows;
$this->form_validation->set_rules('person_tags[]', 'Tags', 'required');
If there are other validation errors, the form re-appears with a list of validation errors but, unfortunately, it doesn't repopulate the form_multiselect() with the originally selected items, as expected. Also, I noticed that if I remove the validation rule for person_tags, when there are other errors on the form, person_tags multiselect() repopulations the list with the originally selected items. How is validation supposed to work? It seems to remove or transform the post.

Answer 1

Instead of defining set_value() with name[], try providing it without them. I created a demo and it works for me. See if this works for you as well.
View
<?php
$attributes = array('method' => 'POST');
echo form_open('home/form', $attributes);
$options = array(
'small' => 'Small Shirt',
'med' => 'Medium Shirt',
'large' => 'Large Shirt',
'xlarge' => 'Extra Large Shirt',
);
$attribute_tag = array(
'class' => 'some-class',
);
// this is the one you should be paying attention to ↓↓
echo form_multiselect('person_tags[]', $options, set_value('person_tags'), $attribute_tag);
$data = array(
'type' => 'text',
'name' => 'email',
'id' => 'email',
);
echo form_input($data, set_value('email'));
echo form_submit('mysubmit', 'Submit Post!');
echo form_close();
?>
Controller
function form(){
$this->load->library('form_validation');
$this->form_validation->set_rules('person_tags[]', 'Tags', 'required');
$this->form_validation->set_rules('email', 'text', 'required');
if ($this->form_validation->run() == FALSE){
$this->load->view('vwHome');
}else{
echo 'No validation error'; die; // save in database(Your logic)
}
}
TL;DR
Change your current code to-
echo form_multiselect('person_tags[]', $options, set_value('person_tags'), $attribute_tag);