Feature: trigger onChange event when the flag dropdown value is changed about intl_phone_field

[ShohidulProgrammer]

I made a solution for this

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

import 'model/countries.dart';
import 'model/mobile_number_info.dart';

class IntlPhoneField extends StatefulWidget {
  final bool obscureText;
  final TextAlign textAlign;
  final VoidCallback onTap;

  /// {@macro flutter.widgets.editableText.readOnly}
  final bool readOnly;
  final FormFieldSetter<MobileNumberInfo> onSaved;

  /// {@macro flutter.widgets.editableText.onChanged}
  ///
  /// See also:
  ///
  ///  * [inputFormatters], which are called before [onChanged]
  ///    runs and can validate and change ("format") the input value.
  ///  * [onEditingComplete], [onSubmitted], [onSelectionChanged]:
  ///    which are more specialized input change notifications.
  final ValueChanged<MobileNumberInfo> onChanged;
  final FormFieldValidator<String> validator;
  final bool autoValidate;

  /// {@macro flutter.widgets.editableText.keyboardType}
  final TextInputType keyboardType;

  /// Controls the text being edited.
  ///
  /// If null, this widget will create its own [TextEditingController].
  final TextEditingController controller;

  /// Defines the keyboard focus for this widget.
  ///
  /// The [focusNode] is a long-lived object that's typically managed by a
  /// [StatefulWidget] parent. See [FocusNode] for more information.
  ///
  /// To give the keyboard focus to this widget, provide a [focusNode] and then
  /// use the current [FocusScope] to request the focus:
  ///
  /// ```dart
  /// FocusScope.of(context).requestFocus(myFocusNode);
  /// ```
  ///
  /// This happens automatically when the widget is tapped.
  ///
  /// To be notified when the widget gains or loses the focus, add a listener
  /// to the [focusNode]:
  ///
  /// ```dart
  /// focusNode.addListener(() { print(myFocusNode.hasFocus); });
  /// ```
  ///
  /// If null, this widget will create its own [FocusNode].
  ///
  /// ## Keyboard
  ///
  /// Requesting the focus will typically cause the keyboard to be shown
  /// if it's not showing already.
  ///
  /// On Android, the user can hide the keyboard - without changing the focus -
  /// with the system back button. They can restore the keyboard's visibility
  /// by tapping on a text field.  The user might hide the keyboard and
  /// switch to a physical keyboard, or they might just need to get it
  /// out of the way for a moment, to expose something it's
  /// obscuring. In this case requesting the focus again will not
  /// cause the focus to change, and will not make the keyboard visible.
  ///
  /// This widget builds an [EditableText] and will ensure that the keyboard is
  /// showing when it is tapped by calling [EditableTextState.requestKeyboard()].
  final FocusNode focusNode;

  /// {@macro flutter.widgets.editableText.onSubmitted}
  ///
  /// See also:
  ///
  ///  * [EditableText.onSubmitted] for an example of how to handle moving to
  ///    the next/previous field when using [TextInputAction.next] and
  ///    [TextInputAction.previous] for [textInputAction].
  final void Function(String) onSubmitted;

  /// If false the text field is "disabled": it ignores taps and its
  /// [decoration] is rendered in grey.
  ///
  /// If non-null this property overrides the [decoration]'s
  /// [Decoration.enabled] property.
  final bool enabled;

  /// The appearance of the keyboard.
  ///
  /// This setting is only honored on iOS devices.
  ///
  /// If unset, defaults to the brightness of [ThemeData.primaryColorBrightness].
  final Brightness keyboardAppearance;

  /// Initial Value for the field.
  /// This property can be used to pre-fill the field.
  final String initialValue;

  /// 2 Letter ISO Code
  final String initialCountryCode;

  /// The decoration to show around the text field.
  ///
  /// By default, draws a horizontal line under the text field but can be
  /// configured to show an icon, label, hint text, and error text.
  ///
  /// Specify null to remove the decoration entirely (including the
  /// extra padding introduced by the decoration to save space for the labels).
  final InputDecoration decoration;

  /// The style to use for the text being edited.
  ///
  /// This text style is also used as the base style for the [decoration].
  ///
  /// If null, defaults to the `subtitle1` text style from the current [Theme].
  final TextStyle style;
  final bool showDropdownIcon;

  final BoxDecoration dropdownDecoration;

  /// {@macro flutter.widgets.editableText.inputFormatters}
  final List<TextInputFormatter> inputFormatters;

  /// Placeholder Text to Display in Searchbar for searching countries
  final String searchText;

  /// Color of the country code
  final Color countryCodeTextColor;

  /// Color of the drop down arrow
  final Color dropDownArrowColor;

  IntlPhoneField(
      {this.initialCountryCode,
      this.obscureText = false,
      this.textAlign = TextAlign.left,
      this.onTap,
      this.readOnly = false,
      this.initialValue,
      this.keyboardType = TextInputType.number,
      this.autoValidate = true,
      this.controller,
      this.focusNode,
      this.decoration,
      this.style,
      this.onSubmitted,
      this.validator,
      this.onChanged,
      this.onSaved,
      this.showDropdownIcon = true,
      this.dropdownDecoration = const BoxDecoration(),
      this.inputFormatters,
      this.enabled = true,
      this.keyboardAppearance = Brightness.light,
      this.searchText = 'Search by Country Name',
      this.countryCodeTextColor,
      this.dropDownArrowColor});

  @override
  _IntlPhoneFieldState createState() => _IntlPhoneFieldState();
}

class _IntlPhoneFieldState extends State<IntlPhoneField> {
  Map<String, String> _selectedCountry =
      countries.firstWhere((item) => item['code'] == 'US');
  List<Map<String, String>> filteredCountries = countries;
  FormFieldValidator<String> validator;

  // declare mobile obj
  String _mobileNumber = '';

  @override
  void initState() {
    super.initState();
    if (widget.initialCountryCode != null) {
      _selectedCountry = countries
          .firstWhere((item) => item['code'] == widget.initialCountryCode);
    }
    validator = widget.autoValidate
        ? (value) => value.length != 10 ? 'Invalid Mobile Number' : null
        : widget.validator;
  }

  Future<void> _changeCountry() async {
    filteredCountries = countries;
    await showDialog(
      context: context,
      useRootNavigator: false,
      child: StatefulBuilder(
        builder: (ctx, setState) => Dialog(
          child: Container(
            padding: EdgeInsets.all(10),
            child: Column(
              children: <Widget>[
                TextField(
                  decoration: InputDecoration(
                    suffixIcon: Icon(Icons.search),
                    labelText: widget.searchText,
                  ),
                  onChanged: (value) {
                    setState(() {
                      filteredCountries = countries
                          .where((country) => country['name']
                              .toLowerCase()
                              .contains(value.toLowerCase()))
                          .toList();

                      print('filteredCountries: $value');
                    });
                  },
                ),
                SizedBox(height: 20),
                Expanded(
                  child: ListView.builder(
                    shrinkWrap: true,
                    itemCount: filteredCountries.length,
                    itemBuilder: (ctx, index) => Column(
                      children: <Widget>[
                        ListTile(
                          leading: Text(
                            filteredCountries[index]['flag'],
                            style: TextStyle(fontSize: 30),
                          ),
                          title: Text(
                            filteredCountries[index]['name'],
                            style: TextStyle(fontWeight: FontWeight.w700),
                          ),
                          trailing: Text(
                            filteredCountries[index]['dial_code'],
                            style: TextStyle(fontWeight: FontWeight.w700),
                          ),
                          onTap: () {
                            _selectedCountry = filteredCountries[index];
                            // call onChanged method here for update country code & phone number
                            if (widget.onChanged != null) {
                              widget.onChanged(
                                MobileNumberInfo(
                                  countryISOCode: _selectedCountry['code'],
                                  countryCode: _selectedCountry['dial_code'],
                                  number: _mobileNumber,
                                ),
                              );
                            }
                            Navigator.of(context).pop();
                          },
                        ),
                        Divider(thickness: 1),
                      ],
                    ),
                  ),
                ),
              ],
            ),
          ),
        ),
      ),
    );
    setState(() {});
  }

  @override
  Widget build(BuildContext context) {
    return Row(
      children: <Widget>[
        _buildFlagsButton(),
        SizedBox(width: 8),
        Expanded(
          child: TextFormField(
            initialValue: widget.initialValue,
            readOnly: widget.readOnly,
            obscureText: widget.obscureText,
            textAlign: widget.textAlign,
            textInputAction: TextInputAction.next,
            onTap: () {
              if (widget.onTap != null) widget.onTap();
            },
            controller: widget.controller,
            focusNode: widget.focusNode,
            onFieldSubmitted: (s) {
              if (widget.onSubmitted != null) widget.onSubmitted(s);
            },
            decoration: widget.decoration,
            style: widget.style,
            onSaved: (value) {
              // set mobile number to mobile obj
              _mobileNumber = value;
              if (widget.onSaved != null)
                widget.onSaved(
                  MobileNumberInfo(
                    countryISOCode: _selectedCountry['code'],
                    countryCode: _selectedCountry['dial_code'],
                    number: value,
                  ),
                );
            },
            onChanged: (value) {
              // set mobile number to mobile obj
              _mobileNumber = value;
              if (widget.onChanged != null)
                widget.onChanged(
                  MobileNumberInfo(
                    countryISOCode: _selectedCountry['code'],
                    countryCode: _selectedCountry['dial_code'],
                    number: value,
                  ),
                );
            },
            validator: validator,
            keyboardType: widget.keyboardType,
            inputFormatters: widget.inputFormatters,
            enabled: widget.enabled,
            keyboardAppearance: widget.keyboardAppearance,
          ),
        ),
      ],
    );
  }

  DecoratedBox _buildFlagsButton() {
    return DecoratedBox(
      decoration: widget.dropdownDecoration,
      child: InkWell(
        borderRadius: widget.dropdownDecoration.borderRadius,
        child: Padding(
          padding: const EdgeInsets.symmetric(vertical: 8),
          child: Row(
            mainAxisAlignment: MainAxisAlignment.center,
            children: <Widget>[
              if (widget.showDropdownIcon) ...[
                Icon(
                  Icons.arrow_drop_down,
                  color: widget.dropDownArrowColor,
                ),
                SizedBox(width: 4)
              ],
              Text(
                _selectedCountry['flag'],
                style: TextStyle(fontSize: 24),
              ),
              SizedBox(width: 8),
              FittedBox(
                child: Text(
                  _selectedCountry['dial_code'],
                  style: TextStyle(
                      fontWeight: FontWeight.w700,
                      color: widget.countryCodeTextColor),
                ),
              ),
              SizedBox(width: 8),
            ],
          ),
        ),
        onTap: _changeCountry,
      ),
    );
  }
}

[vanshg395]

Fixed