How to wait for value before calling method Flutter/Dart

I am having a pretty hard time with certain actions in flutter. I currently have a method in an outside class that updates a db that my widget relies on for displaying info. I am correctly updating the values in the db and updating the UI correctly. BUT I am having a hard time getting an input first, THEN having that method function. I have tried having it all in the same body and no dice, I have tried to have the addStock method show the input and does not work. The only thing that has been a ban-aid has been to use Navigator.push to the screen again or using a time delayed. Both have produced undesired consequences. I have also tried having the addStock method inside the displayAmountToADD on pressing okay and does not update UI.

//a button inside the UI
onPressed: () async {
       displayAmountToAdd(context, index);
           setState(() {});
         },
....

Future<void> displayAmountToAdd(
  BuildContext context,
  int index,
) async {
  final _textFieldController = TextEditingController();
  double materialKG = 0;

  showDialog(
    context: context,
    builder: (context) {
      return AlertDialog(
        title: Text('Enter amount to add'),
        content: Row(
          children: <Widget>[
            Expanded(
              child: TextField(
                onChanged: (materialQuanity) {
                  materialKG = double.parse(materialQuanity);
                },
                controller: _textFieldController,
                decoration: InputDecoration(hintText: "KG"),
              ),
            ),
          ],
        ),
        actions: <Widget>[
          TextButton(
            child: Text('OK'),
            onPressed: () {
              materialKG = double.parse(_textFieldController.text);
              addStock(context, mapM[index]['quanity'], mapM[index]['name'],
                  materialKG);

              Navigator.pop(context);
            },
          ),
          TextButton(
              child: Text("Cancel"),
              onPressed: () {
                Navigator.pop(context);
              })
        ],
      );
    },
  );
  //return Future.delayed(Duration(seconds: 4),()=>materialKG); //TRYING TO AVOID THIS
}



//outside the ui file
addStock(
  BuildContext context,
  double currentQuanity,
  String name,
  double amountToAdd
) async {
  //final db = await database;
  double newStock;

  late double materialKG;
newStock=currentQuanity+amountToAdd;
  await db.rawUpdate(
      'UPDATE materials SET quanity = $newStock WHERE name = "$name" ');
  mapM = await db.query('materials'); //update values
  //the following is only because setState is not working properly on other screen

  ScaffoldMessenger.of(context).showSnackBar(SnackBar(
    content: Text("Added $amountToAdd KG to $name"),
  ));
}

>Solution :

displayAmountToAdd and showDialog method are future. Use await before theses to hold method to finish.

A sample example:

const oneSecond = Duration(seconds: 1);
// ···
Future<void> printWithDelay(String message) async {
  await Future.delayed(oneSecond);
  print(message);
}

Learn more about async-await.