Understanding FutureBuilder in Flutter

In Flutter, the FutureBuilder widget is used to create widgets based on the latest snapshot of interaction with a Future. A Future represents the result of an asynchronous operation and can have two states: uncompleted or completed.

1. Introduction to Futures

A Future is an instance of the Future class in Dart. It represents the result of an asynchronous operation and can have two states: uncompleted or completed.

2. Using FutureBuilder

The FutureBuilder widget is used to create widgets based on the latest snapshot of interaction with a Future. It is Stateful in nature, i.e., it internally manages its own state, as we do in Stateful widgets.

3. Constructor of FutureBuilder

The FutureBuilder constructor takes four parameters:

• Key? key: The widget key is essential to addressing the relevant widget.
• Future? future: A Flutter future that can be accessed by the builder function.
• T? initialData: The starting point of the widget that will be used until the future has returned a value.
• required AsyncWidgetBuilder builder: The build strategy used by the builder.

4. AsyncSnapshot

The AsyncSnapshot holds some of the important data regarding the connection, data, error, etc. Some of its important fields are:

• connectionState: The ConnectionState enum can have 4 possible values: none, waiting, active, or done.
• hasData: Indicates whether the snapshot contains data.
• hasError: Indicates whether the snapshot contains an error.
• data: The data contained in the snapshot.
• error: The error contained in the snapshot.

5. Example of FutureBuilder

Here is an example of how to use the FutureBuilder widget:

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
    @override
    Widget build(BuildContext context) {
        return MaterialApp(
            title: 'FutureBuilder Example',
            home: FutureBuilderExample(),
        );
    }
}

class FutureBuilderExample extends StatefulWidget {
    @override
    _FutureBuilderExampleState createState() => _FutureBuilderExampleState();
}

class _FutureBuilderExampleState extends State<futurebuilderexample> {
    Future<string> _future;

    @override
    void initState() {
        super.initState();
        _future = _getData();
    }

    Future<string> _getData() async {
        await Future.delayed(Duration(seconds: 2));
        return 'Data from Future';
    }

    @override
    Widget build(BuildContext context) {
        return Scaffold(
            appBar: AppBar(title: Text('FutureBuilder Example')),
            body: FutureBuilder(
                future: _future,
                builder: (context, snapshot) {
                    if (snapshot.connectionState == ConnectionState.waiting) {
                        return Center(child: CircularProgressIndicator());
                    } else if (snapshot.connectionState == ConnectionState.done) {
                        if (snapshot.hasData) {
                            return Center(child: Text(snapshot.data));
                        } else if (snapshot.hasError) {
                            return Center(child: Text('Error: ${snapshot.error}'));
                        }
                    }
                    return Container();
                },
            ),
        );
    }
}
</string></string></futurebuilderexample>

In this example:

• The FutureBuilder widget is used to create a widget based on the latest snapshot of interaction with a Future.
• The Future is created in the initState method and is used to fetch data after a delay of 2 seconds.
• The builder function is used to build the widget based on the snapshot.
• If the snapshot is in the waiting state, a CircularProgressIndicator is displayed.
• If the snapshot is in the done state and has data, the data is displayed.
• If the snapshot is in the done state and has an error, the error is displayed.

6. Conclusion

The FutureBuilder widget is a powerful tool in Flutter that allows you to create widgets based on the latest snapshot of interaction with a Future. By using the FutureBuilder widget, you can easily handle asynchronous operations and display the result in your app.