İlkokul öğrencileri için eğlenceli hesap makinesi.
Toplama/Çıkarma işlemi yapıyor.
Bu örnekte TextField, FlatButton kullanımlarını üzerine fikir edinebilirsiniz. ekranda 3 saniye görünüp kaybolan yazı ile kullanıcıya hata mesajı gösterebilirsiniz. Divider ’ın şartlı gösterimini görebilirsiniz. kolay gelsin.
import 'package:flutter/material.dart';

final TextEditingController yazi = TextEditingController();
final TextEditingController alt = TextEditingController();
final TextEditingController ust = TextEditingController();
final TextEditingController isaret = TextEditingController();
final TextEditingController sonuc = TextEditingController();

class hesap extends StatefulWidget {
  const hesap({Key key}) : super(key: key);

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

class _hesapState extends State<hesap> {
  @override
  var renk = Colors.white;
  topla() async {
    isaret.text = "+";
    setState(() {
      renk = Colors.black;
    });

    if (yazi.text.length == 0) {
      ust.text = " RAKAM GİR ";
      Future.delayed(const Duration(seconds: 3), () async {
        sil();
      });
    } else if (ust.text.length == 0) {
      ust.text = "  " + yazi.text;
    } else if (alt.text.length == 0) {
      alt.text = yazi.text;
      sonuc.text =
          (double.parse(ust.text) + double.parse(alt.text)).toStringAsFixed(0);
    } else {
      // yazi.clear();
      isaret.clear();
      ust.clear();
      alt.clear();
      sonuc.clear();
      ust.text = yazi.text;
    }

    yazi.clear();
    yazi.selection =
        TextSelection.fromPosition(TextPosition(offset: yazi.text.length));
  }

  cikar() async {
    isaret.text = "-";

    setState(() {
      renk = Colors.black;
    });

    if (yazi.text.length == 0) {
      ust.text = " RAKAM GİR ";
      Future.delayed(const Duration(seconds: 3), () async {
        sil();
      });
    } else if (ust.text.length == 0) {
      ust.text = "  " + yazi.text;
    } else if (alt.text.length == 0) {
      alt.text = yazi.text;
      sonuc.text =
          (double.parse(ust.text) - double.parse(alt.text)).toStringAsFixed(0);
    } else {
      isaret.clear();
      ust.clear();
      alt.clear();
      sonuc.clear();
      setState(() {
        renk = Colors.white;
      });
      ust.text = yazi.text;
    }

    yazi.clear();
    yazi.selection =
        TextSelection.fromPosition(TextPosition(offset: yazi.text.length));
  }

  sil() {
    yazi.clear();

    isaret.clear();
    ust.clear();
    alt.clear();
    sonuc.clear();
    ust.text = yazi.text;
    setState(() {
      renk = Colors.white;
    });
    yazi.selection =
        TextSelection.fromPosition(TextPosition(offset: yazi.text.length));
  }

  Widget build(BuildContext context) {
    var yukseklik = MediaQuery.of(context).size.width; //Tasarım ayarları
    yukseklik = yukseklik / 1.5;
    return Scaffold(
      body: ListView(
        //Taşmalarda patlamasın diye
        children: <Widget>[
          Column(
            mainAxisAlignment: MainAxisAlignment.start,
            children: <Widget>[
              Padding(
                padding: const EdgeInsets.all(8.0),
                child: TextField(
                  controller: ust,
                  enabled: false,
                  showCursor: false,
                  readOnly: true,
                  style: TextStyle(fontSize: yukseklik / 5),
                  textAlign: TextAlign.center,
                  decoration: InputDecoration(
                    border: OutlineInputBorder(
                      borderSide: BorderSide.none,
                    ),
                  ),
                ),
              ),
              Row(
                mainAxisAlignment: MainAxisAlignment.start,
                children: <Widget>[
                  Flexible(
                    fit: FlexFit.loose,
                    flex: 1,
                    child: Padding(
                      padding: const EdgeInsets.all(8.0),
                      child: TextField(
                        controller: isaret,
                        enabled: false,
                        showCursor: false,
                        readOnly: true,
                        style: TextStyle(fontSize: yukseklik / 5),
                        textAlign: TextAlign.start,
                        decoration: InputDecoration(
                          border: OutlineInputBorder(
                            borderSide: BorderSide.none,
                          ),
                        ),
                      ),
                    ),
                  ),
                  Flexible(
                    fit: FlexFit.tight,
                    flex: 6,
                    child: Padding(
                      padding: const EdgeInsets.all(8.0),
                      child: TextField(
                        controller: alt,
                        enabled: false,
                        showCursor: false,
                        readOnly: true,
                        style: TextStyle(fontSize: yukseklik / 5),
                        textAlign: TextAlign.center,
                        decoration: InputDecoration(
                          border: OutlineInputBorder(
                            borderSide: BorderSide.none,
                          ),
                        ),
                      ),
                    ),
                  ),
                ],
              ),
              Divider(//mayhemious
                color: renk,
                thickness: 5,
                endIndent: 10,
                indent: 10,
              ),
              Padding(
                padding: const EdgeInsets.all(8.0),
                child: TextField(
                  controller: sonuc,
                  enabled: false,
                  showCursor: false,
                  readOnly: true,
                  style: TextStyle(fontSize: yukseklik / 5),
                  textAlign: TextAlign.center,
                  decoration: InputDecoration(
                    border: OutlineInputBorder(
                      borderSide: BorderSide.none,
                    ),
                  ),
                ),
              ),
              Row(
                crossAxisAlignment: CrossAxisAlignment.center,
                children: <Widget>[
                  Flexible(
                    fit: FlexFit.loose,
                    flex: 1,
                    child: FlatButton(
                      child: Text(
                        "+",
                        style: TextStyle(fontSize: yukseklik / 5),
                      ),
                      onPressed: () => topla(),
                    ),
                  ),
                  Flexible(
                    fit: FlexFit.tight,
                    flex: 6,
                    child: Padding(
                      padding: const EdgeInsets.all(8.0),
                      child: TextField(
                        autofocus: true,
                        controller: yazi,
                        decoration: InputDecoration(
                          border: OutlineInputBorder(
                            borderSide: BorderSide(
                              color: Colors.blue,
                              width: 5,
                            ),
                            borderRadius: BorderRadius.all(Radius.circular(10)),
                          ),
                        ),
                      ),
                    ),
                  ),
                  Flexible(
                    fit: FlexFit.loose,
                    flex: 1,
                    child: FlatButton(
                      child: Text(
                        "-",
                        style: TextStyle(fontSize: yukseklik / 5),
                      ),
                      onPressed: () => cikar(),
                    ),
                  ),
                ],
              ),
              Row(
                crossAxisAlignment: CrossAxisAlignment.start,
                children: <Widget>[
                  Expanded(
                    child: FlatButton(
                      child: Text(
                        "1",
                        style: TextStyle(fontSize: yukseklik / 5),
                      ),
                      onPressed: () {
                        yazi.text = yazi.text + "1";
                        yazi.selection = TextSelection.fromPosition(
                            TextPosition(
                                offset: yazi.text
                                    .length)); //Cursor ekranın solunda kalsın
                      },
                    ),
                  ),
                  Expanded(
                    child: FlatButton(
                      child: Text(
                        "2",
                        style: TextStyle(fontSize: yukseklik / 5),
                      ),
                      onPressed: () {
                        yazi.text = yazi.text + "2";
                        yazi.selection = TextSelection.fromPosition(
                            TextPosition(offset: yazi.text.length));
                      },
                    ),
                  ),
                  Expanded(
                    child: FlatButton(
                      child: Text(
                        "3",
                        style: TextStyle(fontSize: yukseklik / 5),
                      ),
                      onPressed: () {
                        yazi.text = yazi.text + "3";
                        yazi.selection = TextSelection.fromPosition(
                            TextPosition(offset: yazi.text.length));
                      },
                    ),
                  ),
                ],
              ),
              Row(
                crossAxisAlignment: CrossAxisAlignment.center,
                children: <Widget>[
                  Expanded(
                    child: FlatButton(
                      child: Text(
                        "4",
                        style: TextStyle(fontSize: yukseklik / 5),
                      ),
                      onPressed: () {
                        yazi.text = yazi.text + "4";
                        yazi.selection = TextSelection.fromPosition(
                            TextPosition(offset: yazi.text.length));
                      },
                    ),
                  ),
                  Expanded(
                    child: FlatButton(
                      child: Text(
                        "5",
                        style: TextStyle(fontSize: yukseklik / 5),
                      ),
                      onPressed: () {
                        yazi.text = yazi.text + "5";
                        yazi.selection = TextSelection.fromPosition(
                            TextPosition(offset: yazi.text.length));
                      },
                    ),
                  ),
                  Expanded(
                    child: FlatButton(
                      child: Text(
                        "6",
                        style: TextStyle(fontSize: yukseklik / 5),
                      ),
                      onPressed: () {
                        yazi.text = yazi.text + "6";
                        yazi.selection = TextSelection.fromPosition(
                            TextPosition(offset: yazi.text.length));
                      },
                    ),
                  ),
                ],
              ),
              Row(
                crossAxisAlignment: CrossAxisAlignment.center,
                children: <Widget>[
                  Expanded(
                    child: FlatButton(
                      child: Text(
                        "7",
                        style: TextStyle(fontSize: yukseklik / 5),
                      ),
                      onPressed: () {
                        yazi.text = yazi.text + "7";
                        yazi.selection = TextSelection.fromPosition(
                            TextPosition(offset: yazi.text.length));
                      },
                    ),
                  ),
                  Expanded(
                    child: FlatButton(
                      child: Text(
                        "8",
                        style: TextStyle(fontSize: yukseklik / 5),
                      ),
                      onPressed: () {
                        yazi.text = yazi.text + "8";
                        yazi.selection = TextSelection.fromPosition(
                            TextPosition(offset: yazi.text.length));
                      },
                    ),
                  ),
                  Expanded(
                    child: FlatButton(
                      child: Text(
                        "9",
                        style: TextStyle(fontSize: yukseklik / 5),
                      ),
                      onPressed: () {
                        yazi.text = yazi.text + "9";
                        yazi.selection = TextSelection.fromPosition(
                            TextPosition(offset: yazi.text.length));
                      },
                    ),
                  ),
                ],
              ),
              Row(
                crossAxisAlignment: CrossAxisAlignment.center,
                children: <Widget>[
                  Expanded(
                    child: FlatButton(
                      child: Text(
                        "=",
                        style: TextStyle(fontSize: yukseklik / 5),
                      ),
                      onPressed: () => isaret.text == "+" ? topla() : cikar(),
                    ),
                  ),
                  Expanded(
                    child: FlatButton(
                      child: Text(
                        "0",
                        style: TextStyle(fontSize: yukseklik / 5),
                      ),
                      onPressed: () {
                        yazi.text = yazi.text + "0";
                        yazi.selection = TextSelection.fromPosition(
                            TextPosition(offset: yazi.text.length));
                      },
                    ),
                  ),
                  Expanded(
                    child: FlatButton(
                      child: Text(
                        "Sil",
                        style: TextStyle(fontSize: yukseklik / 5),
                      ),
                      onPressed: () => sil(),
                    ),
                  ),
                ],
              ),
            ],
          ),
        ],
      ),
    );
  }
}