I am new Flutter and I am facing a problem and I have no idea why.
In Below code when choose value from DropDown it change value of "selectedMonths" But when i select DataRow it uses the default value "1". Please anyone help me with this.

vehicleFeeData(List<VehicleFee>? list) {
    return Padding(
        padding: EdgeInsets.fromLTRB(0, 0, 0, 10),
        child: SingleChildScrollView(
          scrollDirection: Axis.horizontal,
          child: DataTable(
            showCheckboxColumn: true,
            headingRowColor: MaterialStateProperty.all(Colors.yellow[50]),
            border: TableBorder.all(color: Colors.grey[200]!),
            columnSpacing: 20,
            columns: [
              DataColumn(label: Text('Plate Number')),
              DataColumn(label: Text('Exp Date')),
              DataColumn(label: Text('Monthly Fee')),
              DataColumn(label: Text('Months')),
            ],
            rows: list!.map((fee) {

              int selectedMonths = 1; // This value

              return DataRow(
                  selected: vehiclesFee!.contains(fee),
                  onSelectChanged: (selected) {
                    if (vehiclesFee!.contains(fee)) {
                      state!(() {
                        print(selectedMonths);
                        vehiclesFee!.remove(fee);
                        vehiclesFeeTotal -=
                            (int.parse(fee.monthlyFee!) * selectedMonths);
                      });
                    } else {
                      state!(() {
                        print(selectedMonths);
                        vehiclesFee!.add(fee);
                        vehiclesFeeTotal  =
                            (int.parse(fee.monthlyFee!) * selectedMonths);
                      });
                    }
                  },
                  cells: [
                    DataCell(Text(fee.plateNumber!)),
                    DataCell(Text(fee.expDate!.toString().split('00').first)),
                    DataCell(Text(fee.monthlyFee!)),
                    DataCell(Container(
                      width: getProportionateScreenWidth(135),
                      child: DropdownButtonFormField(
                        onChanged: (value) {
                          state!(() {
                            selectedMonths = int.parse(value.toString());
                            print(selectedMonths);
                          });
                        },
                        decoration: InputDecoration(
                          contentPadding:
                              EdgeInsets.symmetric(horizontal: 5, vertical: 5),
                          border: border,
                          enabledBorder: border,
                          errorBorder: border,
                          focusedBorder: border,
                          focusedErrorBorder: border,
                          hintText: "Select Months",
                        ),
                        items: popUpMenuItem,
                      ),
                    )),
                  ]);
            }).toList(),
          ),
        ));
  }

CodePudding user response：

you missed to use value in dropdown

DropdownButtonFormField(
                        onChanged: (value) {
                          state!(() {
                            selectedMonths = int.parse(value.toString());
                            print(selectedMonths);
                          });
                        },
                        value: selectedMonths, // here need to change 
                        decoration: InputDecoration(
                          contentPadding:
                              EdgeInsets.symmetric(horizontal: 5, vertical: 5),
                          border: border,
                          enabledBorder: border,
                          errorBorder: border,
                          focusedBorder: border,
                          focusedErrorBorder: border,
                          hintText: "Select Months",
                        ),
                        items: popUpMenuItem,
                      ),

CodePudding user response：

You should declare int selectedMonths = 1; outside the build method because when you call !state and the widget rebuild, selectedMonths's value initializes to 1 again.