The title: of AppBar is Text. If the Body has ListView that was made out of Stream. How can the Text in the title reflect the ListView number of items.

    build(BuildContext context) {
      return Scaffold(
      appBar:AppBar(title: generateTitle()) // <-- how to pass the snapshot.requiredData.length into here?
      body: StreamBuilder(
        stream: theStream();
        builder:(BuildContext context, AsyncSnapshot<List<AnObject>> snapshot) {
          return ListView.builder(
            itemCount: snapshot.requireData.length,            
            itemBuilder: (context, index) =>
              CardFromAnObject(snapshot,snapshot.requireData[index], context),
          )
        }
      )
   )
}

CodePudding user response：

You can take help from addPostFrameCallback and update the count. I am using counterStream for this example.

class _TSCState extends State<TSC> {
  var counterStream =
      Stream<int>.periodic(const Duration(seconds: 1), (x) => x).take(15);

  int? itemsCount;
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
          title: itemsCount != null
              ? Text("total $itemsCount")
              : Text("loading") // null // or use others expression
          ),
      body: StreamBuilder<int>(
        stream: counterStream,
        builder: (context, snapshot) {
          if (snapshot.hasData) {
            WidgetsBinding.instance!.addPostFrameCallback((timeStamp) {
              setState(() {
                itemsCount = snapshot.data!;
              });
            });
            return ListView.builder(
              itemCount: snapshot.data!,
              itemBuilder: (context, index) => ListTile(
                title: Text("Item $index"),
              ),
            );
          } else {
            //handle others state
            return CircularProgressIndicator();
          }
        },
      ),
    );
  }
}

CodePudding user response：

I implemented my suggestion by using Yeasin Sheikh's sample code.

Because stream generator make a int value in sample code,
I used 'snapshot.requiredData' instead of 'snapshot.requiredData.length'.

import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
        visualDensity: VisualDensity.adaptivePlatformDensity,
      ),
      home: TSCState(),
    );
  }
}

class TSCState extends StatefulWidget {
  TSCState({Key key}) : super(key: key);

  @override
  _TSCStateState createState() => _TSCStateState();
}

class _TSCStateState extends State<TSCState> {
  var counterStream =
      Stream<int>.periodic(const Duration(seconds: 1), (x) => x).take(15);

  int itemsCount;
  @override
  Widget build(BuildContext context) {
    return StreamBuilder<int>(
      stream: counterStream,
      builder: (context, snapshot) {
        if (snapshot.hasData) {
          return Scaffold(
            appBar: AppBar(
              title: Text("total ${snapshot.requireData}"),
            ),
            body: ListView.builder(
              itemCount: snapshot.data,
              itemBuilder: (context, index) => ListTile(
                title: Text("Item $index"),
              ),
            ),
          );
        } else {
          return Scaffold(
            appBar: AppBar(title: Text("total")),
            body: CircularProgressIndicator(),
          );
        }
      },
    );
  }
}

CodePudding user response：

You can add addPostFrameCallback to count your data items and then use totalItem in Appbar.

    build(BuildContext context) {
      return Scaffold(
      appBar:AppBar(title: generateTitle())
      body: StreamBuilder(
        stream: theStream();
        builder:(BuildContext context, AsyncSnapshot<List<AnObject>> snapshot) {

              if (snapshot.data.length > 0) {
                                      SchedulerBinding.instance
                                          .addPostFrameCallback((_) => setState(() {
                                        totalItem = snapshot.data.length;
                                      }));
              }
          return ListView.builder(
            itemCount: snapshot.requireData.length,            
            itemBuilder: (context, index) =>
              CardFromAnObject(snapshot,snapshot.requireData[index], context),
          );
        }
      ));}