ACF Dynamic select values not showing data - wordpress

Question

This question makes me crazy for almost 2 weeks. I know I am not expert in Wordpress, so I am seeking for help here.
I have create a href that when user click it will go to new page.
Add Class2
This href post the Post id. Url display:
[http://localhost/dev6/create-class/?post=289][1]
create-class page:
At create-class page,I am using GET method to display post id from url
$post = $_GET['post'];
I have acf form in create-class page for create new post. In this form, there have dynamic select field but the select field not display any data.
<?php acf_form(array(
'post_id' => 'new_post',
'field_groups' => array(150),
'post_title' => false,
'post_content' => false,
'new_post' => array(
'post_type' => 'classes',
'post_status' => 'publish',
),
'return' => '%post_url%',
'submit_value' => 'Submit',
//'updated_message' => 'Course Submit!',
)); ?>
in my function.php I create function for dynamic select:
function acf_load_t_first_name2_field_choices($field) {
global $post;
//$post = $_GET['post'];
// reset choices
$field['choices'] = array();
// get the textarea value from options page without any formatting
$choices = get_field('t_first_name',$post->ID);
// loop through array and add to field 'choices'
if( is_array($choices) ) {
foreach( $choices as $choice ) {
$field['choices'][ $choice ] = $choice;
}
}
// return the field
return $field;
}
add_filter('acf/load_field/name=t_first_name2', 'acf_load_t_first_name2_field_choices');
Is there something wrong with my code?

Answer 1

I don't believe this will work in your create-class template:
$post = $_GET['post'];
You will need to set something like this up in your functions.php file:
function custom_query_vars_filter($vars) {
$vars[] .= 'post';
return $vars;
}
add_filter( 'query_vars', 'custom_query_vars_filter' );
Then, in your create-class template you can get the variable from the URL like this:
$post = get_query_var('post');
See if that gets you going in the right direction.