How to input "id" field in UI (form engine)?

I didn’t find where the ID field was entered, and when I got the FormModel, I found that the ID in the option was null.

The id is on the general tab. It will get auto set if you change the label.


Sorry, I didn’t make it clear. What I want to say is key in option.

In the open source forms builder UI, a process variable with the id of dropdown box is set with the string value of the selected option. If you need the the variable to be set differently from the text, you can use an expression pointing to a list of Options (or the JSON representation of one). An Option just contains an id and name.