1-) FLUTTER - içerden dışarıya Function onclick interface gibi tetikleme class ve widget kullanımı

  Örnek olarak anlatırsam. bir tane tarih seç widgetim var. bunları tüm sayfalarda onlarca kod yazmak yerine . tek bir class a yazarım. ve içine function göndererim. bu function dışarıya veri aktarmamıza yarıyacak. bu sayede interface gibi kullanırım. tüm sayfalarda bu class ı çağırırım ve kod kalabalığından kurtulurum..

1-) WİDGET İLE

ButtonGonder.dart

import 'package:flutter/material.dart';
class ButtonGonder extends StatefulWidget {
  final Function onClick;
  const ButtonGonder({required this.onClick,Key? key}) : super(key: key);
  @override
  State<ButtonGonder> createState() => _ButtonGonderState();
}

class _ButtonGonderState extends State<ButtonGonder> {
  @override
  Widget build(BuildContext context) {
    return Padding(
      padding: EdgeInsets.only(top: 10),
      child: Align(
        alignment: Alignment.centerRight,
        child: Container(
          margin: const EdgeInsets.only(right: 15),
          height: 50,
          width: 50,
          decoration: BoxDecoration(
            boxShadow: [
              BoxShadow(
                color: Colors.green[200]!.withOpacity(0.5),
                spreadRadius: 5,
                blurRadius: 7,
                offset: const Offset(0, 3),
              ),
            ],
            shape: BoxShape.circle,
            gradient: const LinearGradient(
              begin: Alignment.centerLeft,
              end: Alignment.centerRight,
              colors: [
                Color(0xff1bccba),
                Color(0xff22e2ab),
              ],
            ),
          ),
          child: new IconButton(
            onPressed: () {
              widget.onClick();
            },
            icon: new Icon(Icons.arrow_forward_outlined),
          ),
        ),
      ),
    );
  }
}

KULLANIMI :

ButtonGonder(
  onClick: () {
    EasyLoading.showToast("Gönderildi...");
  },
)

2-) CLASS İLE

TarihSecWidget.dart

import 'package:date_format/date_format.dart';
import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:flutter_easyloading/flutter_easyloading.dart';

class TarihSecWidget {
  String secilenTarih = "";

  int yil = 2022;
  int ay = 03;
  int gun = 03;

  late DateTime secilenTar;

  TarihSecWidget([DateTime? secilenTar = null]) {
    // TarihSecWidget tar = new TarihSecWidget(DateTime.now()) veya DateTime(1980, 01, 01);

    if (secilenTar == null) {
      DateTime suan =DateTime.now();
      secilenTarih = formatDate(suan, [yyyy, '-', mm, '-', dd]);
      yil = suan.year;
      ay = suan.month;
      gun = suan.day;
    } else {
      secilenTarih = formatDate(secilenTar, [yyyy, '-', mm, '-', dd]);
      yil = secilenTar.year;
      ay = secilenTar.month;
      gun = secilenTar.day;
    }

  }

  void showDatePicker(ctx, Function onClick) {
    // showCupertinoModalPopup is a built-in function of the cupertino library

    if (secilenTarih == "") {
      secilenTarih = " ";
    }

    showCupertinoModalPopup(
      context: ctx,
      builder: (_) => Container(
        height: 300,
        color: const Color.fromARGB(255, 255, 255, 255),
        child: Column(
          children: [
            SizedBox(
              height: 200,
              child: CupertinoDatePicker(
                mode: CupertinoDatePickerMode.date,
                initialDateTime: DateTime(yil, ay, gun),
                onDateTimeChanged: (value) {
                  print(value.toString());
                  print(formatDate(value, [yyyy, '-', mm, '-', dd]));
                  secilenTarih = formatDate(value, [yyyy, '-', mm, '-', dd]);

                  EasyLoading.showToast(secilenTarih);

                  onClick(secilenTarih);
                },
              ),
            ),

            // Close the modal
            CupertinoButton(
              child: const Text('OK'),
              onPressed: () {
                if (secilenTarih.trim() == "") {
                  secilenTarih = formatDate(DateTime.now(), [yyyy, '-', mm, '-', dd]);
                }

                EasyLoading.showToast(secilenTarih);

                onClick(secilenTarih);

                Navigator.of(ctx).pop();
              },
            )
          ],
        ),
      ),
    );
  }
}

KULLANIMI :

TarihSecWidget tar = new TarihSecWidget(); // VARSAYILAN BUGUN DÜR
tar.showDatePicker(context, (secilenTarih) {
  setState(() {
    dogumTar.text = secilenTarih;
  });
});

VEYA

TarihSecWidget tar = new TarihSecWidget(DateTime(1980, 01, 01));
tar.showDatePicker(context, (secilenTarih) {
  setState(() {
    dogumTar.text = secilenTarih;
  });
});

DİĞER KOD

late TextEditingController dogumTar;

@override
void initState() {
   super.initState();
  dogumTar = new TextEditingController();

//dogumTar = new TextEditingController(text:formatDate(DateTime.now(), [yyyy, '-', mm, '-', dd]));

}

TextFormField(
  controller: dogumTar,
  onTap: () {
    // Below line stops keyboard from appearing
    FocusScope.of(context)
        .requestFocus(new FocusNode());

    EasyLoading.showToast("tıkladım");

    // _showDatePicker(context);
  TarihSecWidget tar = new TarihSecWidget(DateTime(1980, 01, 01));
tar.showDatePicker(context, (secilenTarih) {
  setState(() {
    dogumTar.text = secilenTarih;
  });
});

  },

  style: TextStyle(
      fontSize: 17, fontWeight: FontWeight.bold),
  keyboardType: TextInputType.emailAddress,
  decoration: InputDecoration(
    labelText: LocaleKeys.dogumtarihiniseciniz.tr(),
    border: OutlineInputBorder(),
    labelStyle: TextStyle(fontSize: 13),
  ),
),