Registers a callback that's called when text in the textbox changes.

In particular, the callback is called when:

  - The user types a new value and then either the textbox loses focus or the user presses enter.

  - A new value is set programmatically with set('value', newValue).

Returns an ID which can be passed to unlisten() to unregister the callback.

this: ui.textboxui.TextboxThe ui.Textbox instance.
callbackFunctionThe callback to fire when the text changes. The callback is passed the text currently in the textbox and the textbox widget.