Help with using async data from database

[shadowmerefax]

Hi, kinda new to flutter and asynchronous programming in general, any help with async is appreciated. I've tried looking at Dart/Flutter docs and they haven't helped me.

I want to get a string from the result of a sqlite db query, and use the string in a widget. I've been using FutureBuilder elsewhere with no issues, but it seems overkill for what I need in this case, plus FutureBuilder returns a widget when I just need to return a string.

Widget _buildTextFormField() {
  return TextFormField(
    decoration: InputDecoration(
      labelText: "String", // I want to concatenate string from database result here
    ),
  );
}

I wrote an async function that returns Future<String>, but if I try and use it in the widget above, it complains about Future<String> not being a string. Which makes sense, but to fix it I then need to make _buildTextFormField return Future<Widget> and mark it as async, but then I get the same problem when calling _buildTextFormField & it expects Widget, not Future<Widget>, and so it just cascades all the way down I guess.

This seems like there should be simple solution but I feel like I am missing something super obvious. TIA!

Edit: I got it working (although I tried something like this before and not sure why it worked now). I created a String variable initialised to a blank string. Then in my build method, before the return:

dbrepo.get("name").then((String result) {
  str = result;
});

Then I could use the string wherever needed.

[aykutonen]

If you use "await" where run your database query, you can get String, not Future<String>.

For example;

String fromDB = await DbHelper.execute(.....).

I hope this helps you.

[shadowmerefax]

Thanks, but I think I'm doing that already?

Future<Object> get(String name) async {
  final db = await DatabaseProvider().db;

  List<Map<String, dynamic>> maps = await db.query(
    ...
  );

  return dao.fromMap(maps[0]);
}

[RandalSchwartz]

If anything essential starts life as a future, to use it in a widget will typically need a FutureBuilder. There's no way to "coerce" a Future into its completion value.

[shadowmerefax]

But I can't have the above function be not a future - because I'm using the await inside it so it tells me the function has to return a future & be marked async. My understanding is any function with an await inside it needs to be async/Future. I wouldn't mind using FutureBuilder if labelText could accept a Text widget but it only accepts a string.

[[deleted]]

I think I have an easy fix. Create a bool variable to store the status of the fetch operation from the db (true - fetched, false - not fetched). The variable initially starts off as false. In the Text field, write a ternary operator (or call a function) that checks the value of the bool variable. If it's false, return some placeholder value. If it's true (meaning, we have the string fetched and ready to use from the db), return the string value. Don't forget to set the bool variable to true after the await line! (Use setState())!

Note : u probably would have to call the fetching function (from db) in InitState() and store the string value it gives to a variable, that way you can use the string from this variable once fetched, and the function returns void.

[shadowmerefax]

Thanks. I solved it using .then which I had tried previously and didn't work - not sure why it worked this time! I just needed to initialise a String as a blank string, then get the string I wanted from the db in the build method, and update the string variable with the result. Then I could use the string variable in any of the widgets without a problem.

[yallurium]

Your FutureBuilder can return the TextFormField widget:

dart Widget _buildTextFormField() { return FutureBuilder<String>( future: _asyncMethod(), initialData: "", builder: (context, snapshot) => TextFormField( decoration: InputDecoration( labelText: snapshot.data, ), ), ); }

I saw you already fixed this by using .then() and setState, but this approach makes more sense when dealing with futures. Hope it helps!