how to disable button in flutter

Please make sure variable qrdata.code and isEnable are initialized outside the build method. Every time when setState is called one or both the variables are getting reset.

The problem is whenever setState is pressed it is not rebuilding the button state. so to change the button state wrap your button with StatefulBuilder.

and please call your API in try catch.

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

  @override
  State<DisableButton> createState() => _DisableButtonState();
}

class _DisableButtonState extends State<DisableButton> {
  bool isEnable = false;
  int qrdata = 1;
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: StatefulBuilder(
          builder:
              (BuildContext context, void Function(void Function()) setState) {
            return ElevatedButton.icon(
              style: ButtonStyle(
                  backgroundColor: MaterialStateProperty.all(
                      const Color.fromARGB(255, 53, 121, 87)),
                  padding: MaterialStateProperty.all(const EdgeInsets.all(20)),
                  textStyle: MaterialStateProperty.all(
                      const TextStyle(fontSize: 14, color: Colors.black))),
              onPressed: qrdata != 9 && !isEnable
                  ? () async {
                      setState(() {
                        isEnable = true;
                      });
                      print(">>>> Button is disabled");
                      try {
                        final data = await http.get(
                          Uri.parse(
                              'https://jsonplaceholder.typicode.com/albums/1'),
                        );

                        if (!mounted) return;

                        Navigator.push(
                          context,
                          MaterialPageRoute(
                            builder: (context) => NextPage(
                              data: data.body.toString(),
                            ),
                          ),
                        );

                        print("Api Data >>>> $data.body");
                      } catch (e) {
                        print("Error While fetching data");
                      }
                      setState(() {
                        isEnable = false;
                      });
                      print(">>>> Button is enabled");
                    }
                  : null,

              // : () {},
              icon: const Icon(
                Icons.home_filled,
              ),
              label: Text(isEnable ? "Disabled" : "Enabled",
                  style: const TextStyle(
                    color: Colors.white,
                  )),
            );
          },
        ),
      ),
    );
  }
}

class NextPage extends StatelessWidget {
  const NextPage({Key? key, required this.data}) : super(key: key);
  final String data;
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(),
      body: Center(child: Text("Data : $data")),
    );
  }
}

The problem in your code is setting isEnable to true but not resting to false.

ElevatedButton.icon(
                  style: ButtonStyle(
                      backgroundColor: MaterialStateProperty.all(
                          const Color.fromARGB(255, 53, 121, 87)),
                      padding:
                          MaterialStateProperty.all(const EdgeInsets.all(20)),
                      textStyle: MaterialStateProperty.all(const TextStyle(
                          fontSize: 14, color: Colors.black))),
                  onPressed: qrdata.code != 9 && !isEnable 
                      ?  () async {   
                           setState(() {
                             isEnable = true;
                           });              
                          var url = Uri.parse(
                              '${ApiConstants.baseUrl}${ApiConstants.updateEndpoint}');
                          var responseData = await http.put(url,
                              headers: ApiConstants.headers);
              
                          if (responseData.statusCode == 202) {
                            print(jsonDecode(responseData.body).toString());
                            // ignore: use_build_context_synchronously
                            Navigator.push(
                              context,
                              MaterialPageRoute(
                                  builder: (context) => Dashboard(
                                        data: widget.data,
                                      )),
                            );
                         
                          }
                         //FocusManager.instance.primaryFocus!.unfocus();
                         //  });
                          // setState(() {  <---- Uncomment this code.
                          //  isEnable = false;
                          //   });
                      }
                      :null,
                
                 // : () {},
                  icon: const Icon(
                    Icons.home_filled,
                  ),
                  label: const Text('Entry',
                      style: TextStyle(
                        color: Colors.white,
                      )),
                ),