Get dropdown values based on another dropdown value in flutter

Question

I have a url that returns a json of companies, i use the list of companies to fill a dropdown. there is another url with a parameter that returns a list of warehouses. The second method that gets the warehouses returns an empty json.

Here is the code that gets the companies. This is working alright

  String? _mySelection;
  final String url = "http://url:8000/companies"
  Future<String> getCompanies() async {
    var res = await http
        .get(Uri.parse(url), headers: {
      'Content-Type': 'application/json'
    });
    var resBody = json.decode(res.body)["data"];    // data = map["data"];
    print(resBody);
    setState(() {
      data = resBody;
    });
    print(res);
    return "Sucess";
  }

The code that gets the warehouses is similar.

  Future<String> getWarehouses(company) async {
    late String warehousesUrl = "http://myWarehouseurl?company=$company";
    var warehouseRes = await http
        .get(Uri.parse(warehousesUrl), headers: {
      'Content-Type': 'application/json'
    });
    var warehouseResBody = json.decode(warehouseRes.body)["data"];    // data = map["data"];
    print(warehouseResBody);
    setState(() {
      warehouseData = warehouseResBody;
    });
    print(warehouseRes);
    return "Sucess";
  }

And my initState method

  @override
  void initState() {
    super.initState();
    this.getCompanies();
    this.getWarehouses(_mySelection);
  }

The dropdowns

              new DropdownButton(
                items: data.map((item) {
                  return new DropdownMenuItem(
                    child: new Text(item['company_name']),
                    value: item['company_name'].toString(),
                  );
                }).toList(),
                onChanged: (newVal) {
                  setState(() {
                    _mySelection = newVal.toString();
                    getWarehouses(_mySelection);

                  });
                },
                value: _mySelection,
              ),
              _mySelection != "" ? DropdownButton(
                items: warehouseData.map((item) {
                  return new DropdownMenuItem(
                    child: new Text(item['warehouse_name']),
                    value: item['name'].toString(),
                  );
                }).toList(),
                onChanged: (newVal) {
                  setState(() {
                    _mySelection = newVal.toString();
                  });
                },
                value: _mySelection,
              ) : Container(),

I am not sure why i am unable to get the values for the second dropdown, when i call the method to get the values for the warehouse in the onchange method in the companies dropdown, the data from the warehouses are printed to the console, but the app crushes.

Does this answer your question? [Change selection of dropdown button according to the choice from the previous one, Flutter](https://stackoverflow.com/questions/70082325/change-selection-of-dropdown-button-according-to-the-choice-from-the-previous-on) — Md. Yeasin Sheikh, Dec 21 '21 at 12:11
@YeasinSheikh no it doesn't, Thank you for suggesting it though. — winfred adrah, Dec 21 '21 at 12:31
are you retrieving data on `initstate`? does below answer solve the issue? — Md. Yeasin Sheikh, Dec 21 '21 at 12:33
No, it does not answer my question. I am retrieving the data after a particular item is selected — winfred adrah, Dec 21 '21 at 14:11

score 0 · Answer 1 · answered Dec 21 '21 at 12:12

I think you miss the async/await, lets try

new DropdownButton(
                items: data.map((item) {
                  return new DropdownMenuItem(
                    child: new Text(item['company_name']),
                    value: item['company_name'].toString(),
                  );
                }).toList(),
                onChanged: (newVal) async{ // here need the change
                  setState(() {
                    _mySelection = newVal.toString();
                    await getWarehouses(_mySelection); // also here add the await

                  });
                },
                value: _mySelection,
              ),

adding await before the method call getWarehouses() means i have to add the async to the setState and not the onChange method — winfred adrah, Dec 21 '21 at 12:41
you can do that, but the question is did you get the solution? — Jahidul Islam, Dec 21 '21 at 12:42

Get dropdown values based on another dropdown value in flutter

1 Answers1