validator property

String? Function(String?)? validator
final

validator for the DropdownTextField to make use of this validator, The SearchField widget needs to be wrapped in a Form and pass it a Global key and write your validation logic in the validator you can define a global key

Form(
 key: _formKey,
 child: SearchField(
   suggestions: _statesOfIndia,
   validator: (state) {
     if (!_statesOfIndia.contains(state) || state.isEmpty) {
       return 'Please Enter a valid State';
     }
     return null;
   },
 )

You can then validate the form by calling the validate function of the form

_formKey.currentState.validate();

Implementation

final String? Function(String?)? validator;