dropdown_overlay_example_4 (final)

import 'dart:async';

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

/// Type definitions for the dropdown widget
typedef ItemFetcher<T> = FutureOr<List<T>> Function();
typedef ItemLabel<T> = String Function(T item);
typedef ItemWidgetBuilder<T> = Widget Function(BuildContext context, T item);
typedef ItemSelected<T> = void Function(T item);
typedef DropdownBuilder<T> = Widget Function(
  BuildContext context,
  List<T> items,
  void Function(T) selectItem,
  bool loading,
  String? error,
);

/// A customizable dropdown widget with asynchronous item loading and filtering
class CustomDropdown<T> extends StatefulWidget {
  final ItemFetcher<T> items;
  final T? selectedItem;
  final ItemLabel<T> itemLabel;
  final ItemWidgetBuilder<T>? itemBuilder;
  final ItemSelected<T>? onSelected;
  final InputDecoration? decoration;
  final DropdownBuilder<T>? dropdownBuilder;
  final FormFieldValidator<T>? validator;
  final AutovalidateMode? autovalidateMode;
  final bool showSearch;

  const CustomDropdown({
    super.key,
    required this.items,
    required this.selectedItem,
    required this.itemLabel,
    this.itemBuilder,
    this.dropdownBuilder,
    this.onSelected,
    this.decoration,
    this.validator,
    this.autovalidateMode,
    this.showSearch = false,
  }) : assert(
          dropdownBuilder != null || itemBuilder != null,
          'You must provide itemBuilder if dropdownBuilder is null',
        );

  @override
  State<CustomDropdown<T>> createState() => _CustomDropdownState<T>();
}

class _CustomDropdownState<T> extends State<CustomDropdown<T>> with WidgetsBindingObserver {
  final TextEditingController _controller = TextEditingController();
  final GlobalKey _fieldKey = GlobalKey();
  final OverlayPortalController _overlayController = OverlayPortalController();
  final ValueNotifier<double> _keyboardHeight = ValueNotifier(0);
  final ValueNotifier<bool> _isOpen = ValueNotifier(false);
  final ValueNotifier<_DropdownState<T>> _state = ValueNotifier(_DropdownState<T>());

  @override
  void initState() {
    super.initState();
    WidgetsBinding.instance.addObserver(this);
  }

  @override
  void dispose() {
    WidgetsBinding.instance.removeObserver(this);
    _controller.dispose();
    _state.dispose();
    _isOpen.dispose();
    _keyboardHeight.dispose();
    super.dispose();
  }

  @override
  void didChangeMetrics() {
    final bottomInset = View.of(context).viewInsets.bottom / View.of(context).devicePixelRatio;
    _keyboardHeight.value = bottomInset;
  }

  /// Loads items asynchronously and updates state
  Future<void> _loadItems() async {
    _state.value = _state.value.copyWith(loading: true, error: null);
    try {
      final items = await widget.items();
      if (!mounted) return;
      _state.value = _state.value.copyWith(
        allItems: items,
        filteredItems: items,
        loading: false,
      );
    } catch (e) {
      if (!mounted) return;
      _state.value = _state.value.copyWith(
        error: 'Failed to load items',
        loading: false,
      );
    }
  }

  /// Toggle the dropdown overlay
  void _toggleOverlay() {
    if (_isOpen.value) {
      _hideOverlay();
    } else {
      _showOverlay();
    }
  }

  /// Shows the dropdown overlay
  void _showOverlay() {
    _loadItems();
    _overlayController.show();
    _isOpen.value = true;
  }

  /// Hides the dropdown overlay
  void _hideOverlay() {
    _overlayController.hide();
    _isOpen.value = false;
    _state.value = _state.value.copyWith(filteredItems: _state.value.allItems);
  }

  /// Filters items based on search query
  void _filterItems(String query) {
    final filtered = _state.value.allItems
        .where((item) => widget.itemLabel(item).toLowerCase().contains(query.toLowerCase()))
        .toList();
    _state.value = _state.value.copyWith(filteredItems: filtered);
  }

  /// Handles item selection
  void _selectItem(T item) {
    final label = widget.itemLabel(item);
    _controller.text = label;

    final fieldState = _fieldKey.currentState as FormFieldState<T>?;
    fieldState?.didChange(item);

    widget.onSelected?.call(item);
    _hideOverlay();
  }

  @override
  Widget build(BuildContext context) {
    return OverlayPortal(
      controller: _overlayController,
      overlayChildBuilder: (context) {
        return ValueListenableBuilder<double>(
          valueListenable: _keyboardHeight,
          builder: (_, keyboardHeight, __) {
            if (_fieldKey.currentContext == null) return const SizedBox.shrink();

            final fieldBox = _fieldKey.currentContext!.findRenderObject() as RenderBox;
            final fieldSize = fieldBox.size;
            final fieldOffset = fieldBox.localToGlobal(Offset.zero);

            final mq = MediaQuery.of(context);
            const minOverlayHeight = 80.0;
            const maxOverlayHeightCap = 400.0;

            final spaceBelow = mq.size.height - fieldOffset.dy - fieldSize.height - keyboardHeight - mq.padding.bottom;
            final spaceAbove = mq.size.height - keyboardHeight - mq.padding.top - 10;

            final openUpward = spaceBelow < 300 && spaceAbove > spaceBelow;

            final availableHeight = openUpward ? spaceAbove : spaceBelow;
            final maxHeight = availableHeight.clamp(minOverlayHeight, maxOverlayHeightCap);

            final top = openUpward
                ? mq.size.height - keyboardHeight - mq.padding.bottom - maxHeight
                : fieldOffset.dy + fieldSize.height;

            return Stack(
              children: [
                // Background tap handler to close overlay
                Positioned.fill(
                  child: GestureDetector(
                    behavior: HitTestBehavior.opaque,
                    onTap: _hideOverlay,
                  ),
                ),
                // Dropdown content
                Positioned(
                  left: fieldOffset.dx,
                  top: top,
                  width: fieldSize.width,
                  height: maxHeight,
                  child: Material(
                    elevation: 8,
                    color: Colors.white,
                    shape: const RoundedRectangleBorder(
                      borderRadius: BorderRadius.all(
                        Radius.circular(12),
                      ),
                    ),
                    child: Column(
                      children: [
                        if (widget.showSearch)
                          Padding(
                            padding: const EdgeInsets.all(8),
                            child: TextField(
                              decoration: InputDecoration(
                                hintText: 'Search...',
                                prefixIcon: const Icon(EvilIcons.search),
                                enabledBorder: OutlineInputBorder(
                                  borderSide: BorderSide(color: Colors.grey.shade300),
                                  borderRadius: BorderRadius.circular(16),
                                ),
                              ),
                              onChanged: _filterItems,
                            ),
                          ),
                        Expanded(
                          child: ValueListenableBuilder<_DropdownState<T>>(
                            valueListenable: _state,
                            builder: (context, state, _) {
                              if (widget.dropdownBuilder != null) {
                                return widget.dropdownBuilder!(
                                    context, state.filteredItems, _selectItem, state.loading, state.error);
                              }
                              if (state.loading) {
                                return const Center(child: CircularProgressIndicator());
                              }
                              if (state.error != null) {
                                return ListTile(
                                  leading: const Icon(Icons.error_outline),
                                  title: Text(state.error!),
                                );
                              }
                              if (state.filteredItems.isEmpty) {
                                return const ListTile(title: Text('No data available'));
                              }
                              return ListView.separated(
                                padding: EdgeInsets.zero,
                                shrinkWrap: true,
                                itemCount: state.filteredItems.length,
                                separatorBuilder: (_, __) => const Divider(height: 1),
                                itemBuilder: (context, index) {
                                  final item = state.filteredItems[index];
                                  return InkWell(
                                    onTap: () => _selectItem(item),
                                    child: widget.itemBuilder!(context, item),
                                  );
                                },
                              );
                            },
                          ),
                        ),
                      ],
                    ),
                  ),
                ),
              ],
            );
          },
        );
      },
      child: FormField<T>(
        key: _fieldKey,
        initialValue: widget.selectedItem,
        validator: widget.validator,
        autovalidateMode: widget.autovalidateMode,
        builder: (FormFieldState<T> field) {
          if (field.value != widget.selectedItem) {
            WidgetsBinding.instance.addPostFrameCallback((_) {
              if (mounted) {
                field.didChange(widget.selectedItem);
                final label = widget.itemLabel(field.value as T);
                _controller.text = label;
              }
            });
          }

          return TextField(
            controller: _controller,
            readOnly: true,
            decoration: (widget.decoration ??
                    InputDecoration(
                      hintText: 'Select...',
                      suffixIcon: ValueListenableBuilder<bool>(
                        valueListenable: _isOpen,
                        builder: (_, isOpen, __) {
                          return Icon(
                            isOpen ? EvilIcons.chevron_up : EvilIcons.chevron_down,
                          );
                        },
                      ),
                    ))
                .copyWith(
              errorText: field.errorText,
            ),
            onTap: _toggleOverlay,
          );
        },
      ),
    );
  }
}

/// State class for dropdown data
class _DropdownState<T> {
  final List<T> allItems;
  final List<T> filteredItems;
  final bool loading;
  final String? error;

  _DropdownState({
    this.allItems = const [],
    this.filteredItems = const [],
    this.loading = true,
    this.error,
  });

  _DropdownState<T> copyWith({
    List<T>? allItems,
    List<T>? filteredItems,
    bool? loading,
    String? error,
  }) {
    return _DropdownState<T>(
      allItems: allItems ?? this.allItems,
      filteredItems: filteredItems ?? this.filteredItems,
      loading: loading ?? this.loading,
      error: error ?? this.error,
    );
  }
}