Show datepicker when field clicked using RxDart way - https://www.facebook.com/groups/1738284952897937/2173932705999824

flutter_field_datetime.dart

import 'package:flutter/material.dart';
import 'package:flutter_test/flutter_test.dart';
import 'package:rxdart/rxdart.dart';

class RiwayatKunjunganBloc {
  final riwayatKunjunganAPI = RiwayatKunjunganAPI();
  final _dateQuery = BehaviorSubject<DateTime>();

  Observable<List<RiwayatKunjunganModel>> _results;

  Function get dateQueryAdd => _dateQuery.sink.add;

  Observable<DateTime> get dateQueryStream => _dateQuery.stream;
  Observable<List<RiwayatKunjunganModel>> get result => _results;

  RiwayatKunjunganBloc() {
    _results = dateQueryStream
        .debounce(Duration(milliseconds: 500))
        .distinct()
        .asyncMap((riwayatKunjunganAPI.fetchDataKunjungan));
  }

  dispose() {
    _dateQuery.close();
  }
}

class RiwayatKunjunganModel {
  final String prefix;
  final DateTime date;

  RiwayatKunjunganModel(this.prefix, this.date);

  String get message => (prefix + ': ${date.month} month');

  @override
  String toString() {
    // TODO: implement toString
    return '$prefix: $date';
  }
}

// fake remote API
class RiwayatKunjunganAPI {
  Future<List<RiwayatKunjunganModel>> fetchDataKunjungan(date) async =>
      [RiwayatKunjunganModel('date', date)];
}

class Vm extends StatefulWidget {
  @override
  VmState createState() {
    return new VmState();
  }
}

class VmState extends State<Vm> {
  final TextEditingController _monthController = TextEditingController();

  RiwayatKunjunganBloc riwayatKunjunganBloc;
  DateTime selectedDate;

  @override
  void initState() {
    super.initState();
    riwayatKunjunganBloc = RiwayatKunjunganBloc();
    riwayatKunjunganBloc.result.listen((results) {
      setState(() {
        final model = results.firstWhere((dm) => dm.date == selectedDate, orElse: () => results.first);
        _monthController.text = model.message;
      });
    });
  }

  @override
  Widget build(BuildContext context) {
    return Material(
      child: Directionality(
        textDirection: TextDirection.ltr,
        child: InkWell(
          onTap: () {
            showDatePicker(
                    context: context,
                    initialDate: selectedDate ?? DateTime.now(),
                    lastDate: DateTime(2020),
                    firstDate: DateTime(2011))
                .then(riwayatKunjunganBloc.dateQueryAdd);
          },
          child: TextField(
            controller: _monthController,
            enabled: false,  // disable show keyboard for now, wait for better solution
            decoration: InputDecoration(
                hintText: 'Pilih Bulan',
                labelText: 'Bulan kunjungan',
                hasFloatingPlaceholder: true),
          ),
        ),
      ),
    );
  }

  @override
  void dispose() {
    riwayatKunjunganBloc.dispose();
    super.dispose();
  }
}

void main() {
  
  testWidgets('bloc datetime picker update the value of field', (tester) async {
    await tester.pumpWidget(MaterialApp(
      home: Vm(),
    ));

    final Finder field = find.byType(InkWell).first;
    final today = DateTime.now();

    await tester.tap(field);

    await tester.pumpAndSettle(const Duration(seconds: 2));

    final Finder previousMonthIcon = find.byWidgetPredicate((Widget w) =>
        w is IconButton && (w.tooltip?.startsWith('Previous month') ?? false));
    await tester.tap(previousMonthIcon.first);
    await tester.pumpAndSettle(const Duration(seconds: 1));
    await tester.tap(find.text('OK'));
    
    // Wait for debounce stream duration is more than on stream
    await tester.pumpAndSettle(Duration(seconds: 1));
    final Finder editableTextFinder =
        find.widgetWithText(TextField, 'date: ${today.month - 1} month');

    expect(editableTextFinder, findsOneWidget);
  });
}