Flutter: I have two function for reading firebase data in my flutter app. now I want to sum two func-CodePudding

I want to sum two different firebase collection field values in my flutter app. That's why I write two functions. I can sum one collection field value but two collection field value sum in a single text widget is not working or I am not understanding how to do this..

Scaffold(
  body: SafeArea(
      child: Container(
    child: StreamBuilder<double?>(
      stream: getFundData(),
      builder: (context, snapshort) {
        if (snapshort.connectionState == ConnectionState.waiting) {
          return Center(child: CircularProgressIndicator());
        }
        if (snapshort.hasData) {
          double data = snapshort.data!;
          return Center(child: Column(
            children: [
              Text("$data"),
              
            ],
          ));
        }

        return Text("data");
      },
    ),
  )),
);

function code

Stream<double> getFundData() async* {
  final result =
  await FirebaseFirestore.instance.collection('Use-of-fund').get();
  double totalFundAmount = 0;
  for (var doc in result.docs) {
    totalFundAmount  = doc['Amount'];
  }
  yield totalFundAmount;
}

Stream<double> getUserBalanceData() async* {
  final result = await FirebaseFirestore.instance.collection('User-data').get();
  double userTotalAmount = 0;
  for (var doc in result.docs) {
    userTotalAmount  = doc['Balance'];
  }
  yield userTotalAmount;
}

Now I want to sum userTotalAmount and totalFundAmount

CodePudding user response：

Use RxDart (Observable package). Specifically, use CombineLatestStream for both getFundData and getUserBalanceData. It is there that you sum the outputs when either streams emit.

// ...

StreamBuilder<double>(
  stream: CombineLatestStream.combine2(
    getFundData(),
    getUserBalanceData(),
    (double a, double b) => a   b,
  ),
  builder: (context, snapshot) {

// ...

Remember that you have to install the rxdart package in your project. Run the following command in a terminal inside your project folder:

flutter pub add rxdart

Then import it at the top of the Dart file

import 'package:rxdart/rxdart.dart';

Explanation

So the problem is you want to be capable of summing the results from two different streams. Mainly because StreamBuilder takes only one Stream at a time. CombineLatestStream above from the rxdart package permits you to do this. The rxdart package provides easy ways to Observables in a reactive programming style. In this case, the streams are all from Firebase. And even if they weren't, you will still do something similar.