Passing a php variable into a gravity forms hook - php

Question

I think I'm getting really confused with return'ing and echo'ing variables.
I've got this gravity forms hook from their support...
add_filter('gform_field_value_facebook_name', 'my_custom_population_function');
function my_custom_population_function($value){
return 'boom!';
}
This works and returns 'boom!' as my form field default variable.
This is pretty straight forward for a general text string, but I am trying to return a PHP variable instead.
I am loading the facebook PHP SDK in my functions.php at a higher scope than the gravity form hook. The facebook SDK definitely works, for example I am currently echoing this in my wordpress theme files...
echo $userData['name']
But my question is, why does it not work if I try and return the above variable inside the gravity for hook?
Please see what I have tried below, but it returns nothing...
add_filter('gform_field_value_facebook_name', 'my_custom_population_function');
function my_custom_population_function($value){
return $userData['name'];
}
I've also tried something similar in my wordpress functions.php, when trying to echo a variable in a filter...
$fb_app_id = '12345678910';
// APP ID FILTER
add_action( 'fb_app_id', 'echo_fb_app_id' );
function echo_fb_app_id() {
echo $fb_app_id;
}
But this returns nothing and the scope is the same.
Can anyone please enlighten me to why I can't pass these variables around. I think thats the technical term. Thank you very much.

Answer 1

This is because in PHP, functions don't read global variables without the global keyword.
$fb_app_id = '12345678910';
// APP ID FILTER
add_action( 'fb_app_id', 'echo_fb_app_id' );
function echo_fb_app_id() {
global $fb_app_id; // tells PHP to use the global variable
echo $fb_app_id;
}
Try to add global $userData; to your my_custom_population_function.