I keep getting message saying "dead code"

I’m trying to make a button that loses opacity when pressed, but I’m getting a message that saying I have dead code so the app won’t work.

main.dart

void main() {
  runApp(const App());
}

class App extends StatelessWidget {
  const App({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(

      home: const LoginButton()
    );
  }
}

The error occurs here, saying the 0.5 in the conditional statement is dead code
login_button

class LoginButton extends StatelessWidget {
  const LoginButton({super.key});

  @override
  Widget build(BuildContext context) {
    bool pressed = false;

    return Scaffold(
      backgroundColor: Colors.black12,
      body: Center(
        child: GestureDetector(
          onTap: (){
            pressed = true;
          } ,
          child: AnimatedOpacity(
            opacity: pressed ? 0.5 : 1,
            duration: const Duration(milliseconds: 800),
            child: Container(
              width: 300,
              height: 50,
              decoration: ShapeDecoration(
                color: const Color(0xFFE9ED1A),
                shape: RoundedRectangleBorder(
                  side: const BorderSide(
                    width: 1.77,
                    color: Color(0xFFE9EC19),
                  ),
                  borderRadius: BorderRadius.circular(6.18),
                ),
              ),
              child: const Center(child: Text('Login')),
            ),
          ),
        ),
      ),
    );
  }
}

>Solution :

First: Since the widget is interactive, it has to be converted to a StatefulWidget.

Second: The bool pressed = false; has to be declared outside of th build method.

Third: The toggling of the pressed (in the GestureDetector – onTap) has to be inside a setState.

Here is the widget including the above fixes:

class LoginButton extends StatefulWidget {
  const LoginButton({super.key});

  @override
  State<LoginButton> createState() => _LoginButtonState();
}

class _LoginButtonState extends State<LoginButton> {
  bool pressed = false;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: Colors.black12,
      body: Center(
        child: GestureDetector(
          onTap: () {
            setState(() {
              pressed = !pressed;
            });
          },
          child: AnimatedOpacity(
            opacity: pressed ? 0.5 : 1,
            duration: const Duration(milliseconds: 800),
            child: Container(
              width: 300,
              height: 50,
              decoration: ShapeDecoration(
                color: const Color(0xFFE9ED1A),
                shape: RoundedRectangleBorder(
                  side: const BorderSide(
                    width: 1.77,
                    color: Color(0xFFE9EC19),
                  ),
                  borderRadius: BorderRadius.circular(6.18),
                ),
              ),
              child: const Center(child: Text('Login')),
            ),
          ),
        ),
      ),
    );
  }
}

Tip:

Additionally, although your code works as expected, it seems the ElevatedButton can be a proper widget instead of having a Container wrapped with GestureDetector.