flutter/lib/widgets/add_exercise/add_exercise_multiselect_button.dart

import 'package:flutter/material.dart';
import 'package:multi_select_flutter/multi_select_flutter.dart';

class AddExerciseMultiselectButton<T> extends StatefulWidget {
  final List<T> items;
  final String title;
  final ValueChanged<List<T?>> onChange;
  final FormFieldSetter<List<T?>?>? onSaved;

  const AddExerciseMultiselectButton({
    Key? key,
    required this.items,
    required this.title,
    required this.onChange,
    this.onSaved,
  }) : super(key: key);

  @override
  _AddExerciseMultiselectButtonState createState() => _AddExerciseMultiselectButtonState<T>();
}

class _AddExerciseMultiselectButtonState<T> extends State<AddExerciseMultiselectButton> {
  List<T?> _selectedItems = [];
  @override
  Widget build(BuildContext context) {
    return Padding(
      padding: const EdgeInsets.all(8.0),
      child: MultiSelectDialogField(
        onSaved: widget.onSaved,
        items: widget.items.map((item) => MultiSelectItem<T?>(item, item.name)).toList(),
        onConfirm: (value) {
          if (value.isNotEmpty) {
            setState(() {
              _selectedItems = value as List<T?>;
              widget.onChange(_selectedItems);
            });
          }
        },
        chipDisplay: MultiSelectChipDisplay<T?>(
          //scroll: true,
          onTap: (value) {
            setState(() {
              _selectedItems.remove(value);
            });
          },
          icon: const Icon(Icons.close),
        ),
        title: Text(widget.title),
        buttonText: Text(
          widget.title,
          style: TextStyle(
            color: _selectedItems.isEmpty ? Colors.grey[700] : Colors.grey,
          ),
        ),
        buttonIcon: Icon(
          Icons.arrow_drop_down,
          color: _selectedItems.isEmpty ? Colors.grey[700] : Colors.grey,
        ),
        decoration: BoxDecoration(
          border: Border.all(
            color: _selectedItems.isEmpty ? Colors.grey : Colors.transparent,
          ),
          borderRadius: const BorderRadius.all(
            Radius.circular(10),
          ),
        ),
      ),
    );
  }
}