This functionality has recently been added to the checkbox field, it was originally only part of the radio field. I imagine that eventually it will find it’s way into the select field as well.
In the mean time, a work-a-round
Create your select field that has a choice of “Other”
Create a text field with conditional logic to show if “Other” is selected for the choice.
That’s the easy bit.
For the saving of the new value as a choice I would recommend looking at the code that does this for the checkbox field
// FROM advanced-custom-fields-pro/fields/checkbox.php LINE 368
// save_other_choice
if( $field['save_custom'] ) {
// get raw $field (may have been changed via repeater field)
// if field is local, it won't have an ID
$selector = $field['ID'] ? $field['ID'] : $field['key'];
$field = acf_get_field( $selector, true );
// bail early if no ID (JSON only)
if( !$field['ID'] ) return $value;
// loop
foreach( $value as $v ) {
// ignore if already eixsts
if( isset($field['choices'][ $v ]) ) continue;
// unslash (fixes serialize single quote issue)
$v = wp_unslash($v);
// append
$field['choices'][ $v ] = $v;
}
// save
acf_update_field( $field );
}
basically, you need to get the current field, update the choices with your addition and then call acf_update_field().
