Całościowe podejście do projektowania aplikacji mobilnych

class LoginPage extends StatelessWidget {
  LoginPage({super.key});

  final emailController = TextEditingController();
  final passwordController = TextEditingController();

  void signUserIn() async  {

    try{
      Response response = await post(
          Uri.parse('https://www.somepage.com/login.php'),
          body: {
            'email' : emailController.text,
            'password' : passwordController.text
          }
      );

      if(response.statusCode == 200){
        var data = jsonDecode(response.body.toString());
        if(data['success'] == 1) {
          print(data['message']);
          
          SharedPreferences prefs = await SharedPreferences.getInstance();
          prefs.setString('email', emailController.text);
          prefs.setString('token', data['token']);



          // ---> tutaj chciałbym przejść do HomePage 

          


        } else {
          print(data['status']);
          print(data['message']);
        }
      }else {
        print('Login failed...');
        print(response.statusCode);
      }
    }catch(e){
      print(e.toString());
    }

  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: Colors.grey[300],
      body: SafeArea(
        child: Center(
          child: SingleChildScrollView(
            child: Column(
              mainAxisAlignment: MainAxisAlignment.center,
              children: [
                const SizedBox(height: 25),

                const Icon(
                  Icons.lock,
                  size: 100,
                ),

                const SizedBox(height: 25),

                Text(
                  'Witamy ponownie!',
                  style: TextStyle(
                    color: Colors.grey[700],
                    fontSize: 16,
                  ),
                ),

                const SizedBox(height: 25),

                MyTextField(
                  controller: emailController,
                  hintText: 'Email',
                  obscureText: false,
                ),

                const SizedBox(height: 10),

                MyTextField(
                  controller: passwordController,
                  hintText: 'Hasło',
                  obscureText: true,
                ),

                const SizedBox(height: 10),

                const Padding(
                  padding: EdgeInsets.symmetric(horizontal: 25.0),
                  child: Row(
                    mainAxisAlignment: MainAxisAlignment.end,
                    children: [
                      Text(
                        'Nie pamiętasz hasła?',
                        style: TextStyle(color: Colors.blue, fontWeight: FontWeight.bold),
                      ),
                    ],
                  ),
                ),

                const SizedBox(height: 20),

                MyButton(
                  onTap: signUserIn,
                ),

                const SizedBox(height: 30),

                Padding(
                  padding: const EdgeInsets.symmetric(horizontal: 25.0),
                  child: Row(
                    children: [
                      Expanded(
                        child: Divider(
                          thickness: 0.5,
                          color: Colors.grey[400],
                        ),
                      ),
                      Padding(
                        padding: const EdgeInsets.symmetric(horizontal: 25.0),
                        child: Text(
                          'Albo kontynuuj z',
                          style: TextStyle(color: Colors.grey[700]),
                        ),
                      ),
                      Expanded(
                        child: Divider(
                          thickness: 0.5,
                          color: Colors.grey[400],
                        ),
                      ),
                    ],
                  ),
                ),

                const SizedBox(height: 30),

                const Row(
                  mainAxisAlignment: MainAxisAlignment.center,
                  children: [
                    SquareTile(imagePath: 'lib/images/google.png'),  
                    SizedBox(width: 10),
                    SquareTile(imagePath: 'lib/images/apple.png')
                  ],
                ),

                const SizedBox(height: 30),

                Row(
                  mainAxisAlignment: MainAxisAlignment.center,
                  children: [
                    Text(
                      'Nie masz konta?',
                      style: TextStyle(color: Colors.grey[700]),
                    ),
                    const SizedBox(width: 4),
                    const Text(
                      'Zarejestruj się',
                      style: TextStyle(color: Colors.blue, fontWeight: FontWeight.bold),
                    ),
                  ],
                )
              ],
          ),
        ),
      ),
    ),
  );
 }
}

class HomePage extends StatelessWidget {
  HomePage({super.key});

  void signUserOut() async {
    SharedPreferences prefs = await SharedPreferences.getInstance();
    prefs.remove('email');
    prefs.remove('token');
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: Colors.grey[300],
      appBar: AppBar(
        backgroundColor: Colors.grey[900],
        actions: [
          IconButton(
            onPressed: signUserOut,
            icon: Icon(Icons.logout),
          )
        ],
      ),
      body: Center(
          child: Text(
        "TEST",
        style: TextStyle(fontSize: 20),
      )),
    );
  }
}

class PostListOfDiets {
  String? nazwa;
  String? opis;
  String? komentarz;
  String? dietetyk;
  int? id;

  PostListOfDiets({this.nazwa, this.opis, this.komentarz, this.dietetyk, this.id});

  PostListOfDiets.fromJson(Map<String, dynamic> json) {
    nazwa = json['nazwa'];
    opis = json['opis'];
    komentarz = json['komentarz'];
    dietetyk = json['dietetyk'];
    id = json['id'];
  }
}

            child: DropdownButtonFormField(
                  hint: const Text("Wybierz jadłospis"),
                  
                  // >>> tu jest część której nie rozumiem
                  items: posts.map<DropdownMenuItem<String>>((String value) {
                  return DropdownMenuItem<String>(
                    value: value,
                    child: Text(value),
                  );
                  }).toList(),
                  //<<<tu jest część której nie rozumiem
                  
                  onChanged: (val) {
                    setState(() {
                      _selectedVal = val as String;
                    });
                  },
                  icon: const Icon(
                    Icons.arrow_drop_down_circle,
                    color: Colors.blue,
                  ),
                  dropdownColor: Colors.grey[200],
                  decoration: const InputDecoration(
                    labelText: "Nazwa jadłospisu",
                    labelStyle: TextStyle(color: Colors.blue, fontSize: 16.0),
                    prefixIcon: Icon(
                      Icons.list_alt,
                      color: Colors.blue,
                    ),
                  ),
                )