8 – Change the Field Instance Settings form to admin / structure / types / manage // fields / node ../ storage

I'm trying to figure out how to add an extra field to the content type field settings page.

Basically, I want to change the field instance setup form Admin / Structure / Types / Manage // Fields / Nodes ../ Memory ,

I go with hook_form_FORM_ID_alter for FORM_ID field_config_edit_form,
The new form element appears on the form, but after submitting, I can not see the value.

Am I missing something? Is an additional form submit function required to submit the new value?

Here is my clipping –

/ **
* Implemented hook_form_FORM_ID_alter ().
* /
Function mymod_form_field_storage_config_edit_form_alter (& $ form,  Drupal  Core  Form  FormStateInterface $ form_state, $ form_id) {

$ form['enabled'] = Array (
& # 39; # type & # 39; => & # 39; checkbox & # 39 ;,
& # 39; # title & # 39; => t (& # 39; Enable & # 39;),
& # 39; # description & # 39; => t (& # 39; When enabled, this module changes the field settings. & # 39;),
& # 39; # default_value & # 39; => $ form['enabled'],
);
}