update selected value when menu is closed.

[djoenee]

Hello, is it possible to update the value of "selectedValue" from outside of the class?
(like when a button is pressed then selectedValue ="abc")
I tried a lot but the the value displays in the box only changes when taped on.
(I don't know how to trigger the Build methode)

void updateSelectedValue(String? newValue) async {
    print("Newvalue: $newValue");
    departValue = selectedValue;
    if (newValue != null) {
      departValue = newValue;
      selectedValue = newValue;
    } else {
      print("newvar is null");
    }
  }

  @override
  void dispose() {
    textEditingController.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    // print(stringList);
    print("buildvalue: $value");
    return Container(
      child: DropdownButtonHideUnderline(
        child: DropdownButton2<String>(
          key: _dropdwnKey,
          isExpanded: true,
          hint: Text(
            'Station',
            style: TextStyle(
              fontSize: 14,
              color: Bcolors.textSecondary,
            ),
          ),
          items: DropdwnState.stringList
              .map((item1) => DropdownMenuItem(
                    value: item1,
                    child: Text(
                      item1,
                      style: const TextStyle(
                        fontSize: 14,
                        color: Bcolors.textSecondary,
                      ),
                    ),
                  ))
              .toList(),
          value: selectedValue,
          **onChanged**: (value) async {
            setState(() {
              print("setState");
              selectedValue = value;
              updateSelectedValue(departValue);
              print("onchanged:$departValue");
            });
          },

The onchanged can trigger a setState , but I have not found another way to trigger a setState, updateSelectedValue would be idealy to to have a setState in ,but then it trouws an error.