onChanged property Null safety
Called when the user initiates a change to the TextField's value: when they have inserted or deleted text.
This callback doesn't run when the TextField's text is changed programmatically, via the TextField's controller. Typically it isn't necessary to be notified of such changes, since they're initiated by the app itself.
onChanged is called before onSubmitted when user indicates completion of editing, such as when pressing the "done" button on the keyboard. That default behavior can be overridden. See onEditingComplete for details.
flutter create --sample=widgets.EditableText.onChanged.1 mysample
final ValueChanged<String>? onChanged;